libpng.3 235 KB

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  1. .TH LIBPNG 3 "February 18, 2012"
  2. .SH NAME
  3. libpng \- Portable Network Graphics (PNG) Reference Library 1.5.9
  4. .SH SYNOPSIS
  5. \fI\fB
  6. \fB#include <png.h>\fP
  7. \fI\fB
  8. \fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
  9. \fI\fB
  10. \fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
  11. \fI\fB
  12. \fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
  13. \fI\fB
  14. \fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
  15. \fI\fB
  16. \fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
  17. \fI\fB
  18. \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
  19. \fI\fB
  20. \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
  21. \fI\fB
  22. \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
  23. \fI\fB
  24. \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
  25. \fI\fB
  26. \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
  27. \fI\fB
  28. \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
  29. \fI\fB
  30. \fBpng_structp png_create_read_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
  31. \fI\fB
  32. \fBpng_structp png_create_read_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
  33. \fI\fB
  34. \fBpng_structp png_create_write_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
  35. \fI\fB
  36. \fBpng_structp png_create_write_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
  37. \fI\fB
  38. \fBvoid png_data_freer (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIfreer\fP\fB, png_uint_32 \fImask)\fP\fB);\fP
  39. \fI\fB
  40. \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
  41. \fI\fB
  42. \fBvoid png_destroy_read_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fP\fIinfo_ptr_ptr\fP\fB, png_infopp \fIend_info_ptr_ptr\fP\fB);\fP
  43. \fI\fB
  44. \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
  45. \fI\fB
  46. \fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
  47. \fI\fB
  48. \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
  49. \fI\fB
  50. \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
  51. \fI\fB
  52. \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
  53. \fI\fB
  54. \fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
  55. \fI\fB
  56. \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
  57. \fI\fB
  58. \fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  59. \fI\fB
  60. \fBpng_uint_32 png_get_bKGD (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
  61. \fI\fB
  62. \fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  63. \fI\fB
  64. \fBpng_uint_32 png_get_cHRM (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
  65. \fI\fB
  66. \fBpng_uint_32 png_get_cHRM_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
  67. \fI\fB
  68. \fBpng_uint_32 png_get_cHRM_XYZ (png_structp \fIpng_ptr,
  69. \fBpng_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*red_X\fP\fB, double \fP\fI*red_Y\fP\fB, double \fI*red_Z,
  70. \fBdouble \fP\fI*green_X\fP\fB, double \fP\fI*green_Y\fP\fB, double \fP\fI*green_Z\fP\fB, double \fI*blue_X,
  71. \fBdouble \fP\fI*blue_Y\fP\fB, double \fI*blue_Z\fP\fB);\fP
  72. \fI\fB
  73. \fBpng_uint_32 png_get_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fI*int_red_X\fP\fB, png_fixed_point \fP\fI*int_red_Y\fP\fB, png_fixed_point \fP\fI*int_red_Z\fP\fB, png_fixed_point \fP\fI*int_green_X\fP\fB, png_fixed_point \fP\fI*int_green_Y\fP\fB, png_fixed_point \fP\fI*int_green_Z\fP\fB, png_fixed_point \fP\fI*int_blue_X\fP\fB, png_fixed_point \fP\fI*int_blue_Y\fP\fB, png_fixed_point \fI*int_blue_Z\fP\fB);\fP
  74. \fI\fB
  75. \fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
  76. \fI\fB
  77. \fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
  78. \fI\fB
  79. \fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  80. \fI\fB
  81. \fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
  82. \fI\fB
  83. \fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  84. \fI\fB
  85. \fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
  86. \fI\fB
  87. \fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
  88. \fI\fB
  89. \fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
  90. \fI\fB
  91. \fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
  92. \fI\fB
  93. \fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  94. \fI\fB
  95. \fBpng_uint_32 png_get_gAMA (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
  96. \fI\fB
  97. \fBpng_uint_32 png_get_gAMA_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
  98. \fI\fB
  99. \fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
  100. \fI\fB
  101. \fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
  102. \fI\fB
  103. \fBpng_uint_32 png_get_hIST (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
  104. \fI\fB
  105. \fBpng_uint_32 png_get_iCCP (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_bytepp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
  106. \fI\fB
  107. \fBpng_uint_32 png_get_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*width\fP\fB, png_uint_32 \fP\fI*height\fP\fB, int \fP\fI*bit_depth\fP\fB, int \fP\fI*color_type\fP\fB, int \fP\fI*interlace_type\fP\fB, int \fP\fI*compression_type\fP\fB, int \fI*filter_type\fP\fB);\fP
  108. \fI\fB
  109. \fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  110. \fI\fB
  111. \fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  112. \fI\fB
  113. \fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
  114. \fI\fB
  115. \fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  116. \fI\fB
  117. \fBpng_const_bytep png_get_io_chunk_name (png_structp \fIpng_ptr\fP\fB);\fP
  118. \fI\fB
  119. \fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
  120. \fI\fB
  121. \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
  122. \fI\fB
  123. \fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
  124. \fI\fB
  125. \fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
  126. \fI\fB
  127. \fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
  128. \fI\fB
  129. \fBpng_uint_32 png_get_oFFs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
  130. \fI\fB
  131. \fBpng_uint_32 png_get_pCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
  132. \fI\fB
  133. \fBpng_uint_32 png_get_pHYs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
  134. \fI\fB
  135. \fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  136. \fI\fB
  137. \fBpng_uint_32 png_get_pHYs_dpi (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
  138. \fI\fB
  139. \fBpng_fixed_point png_get_pixel_aspect_ratio_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  140. \fI\fB
  141. \fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  142. \fI\fB
  143. \fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  144. \fI\fB
  145. \fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
  146. \fI\fB
  147. \fBpng_uint_32 png_get_PLTE (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
  148. \fI\fB
  149. \fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr)
  150. \fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  151. \fI\fB
  152. \fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  153. \fI\fB
  154. \fBpng_uint_32 png_get_sBIT (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
  155. \fI\fB
  156. \fBvoid png_get_sCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, double* \fP\fIwidth\fP\fB, double* \fIheight\fP\fB);\fP
  157. \fI\fB
  158. \fBvoid png_get_sCAL_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_fixed_pointp \fP\fIwidth\fP\fB, png_fixed_pointp \fIheight\fP\fB);\fP
  159. \fI\fB
  160. \fBvoid png_get_sCAL_s (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_charpp \fP\fIwidth\fP\fB, png_charpp \fIheight\fP\fB);\fP
  161. \fI\fB
  162. \fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
  163. \fI\fB
  164. \fBpng_uint_32 png_get_sPLT (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
  165. \fI\fB
  166. \fBpng_uint_32 png_get_sRGB (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int \fI*file_srgb_intent\fP\fB);\fP
  167. \fI\fB
  168. \fBpng_uint_32 png_get_text (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
  169. \fI\fB
  170. \fBpng_uint_32 png_get_tIME (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
  171. \fI\fB
  172. \fBpng_uint_32 png_get_tRNS (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans_alpha\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_color\fP\fB);\fP
  173. \fI\fB
  174. \fB/* This function is really an inline macro. \fI*/
  175. \fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
  176. \fI\fB
  177. \fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
  178. \fI\fB
  179. \fB/* This function is really an inline macro. \fI*/
  180. \fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
  181. \fI\fB
  182. \fBpng_uint_32 png_get_unknown_chunks (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
  183. \fI\fB
  184. \fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
  185. \fI\fB
  186. \fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
  187. \fI\fB
  188. \fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
  189. \fI\fB
  190. \fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
  191. \fI\fB
  192. \fBpng_uint_32 png_get_valid (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
  193. \fI\fB
  194. \fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  195. \fI\fB
  196. \fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  197. \fI\fB
  198. \fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  199. \fI\fB
  200. \fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  201. \fI\fB
  202. \fBpng_uint_32 png_get_x_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  203. \fI\fB
  204. \fBpng_uint_32 png_get_x_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  205. \fI\fB
  206. \fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  207. \fI\fB
  208. \fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  209. \fI\fB
  210. \fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  211. \fI\fB
  212. \fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  213. \fI\fB
  214. \fBpng_uint_32 png_get_y_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  215. \fI\fB
  216. \fBpng_uint_32 png_get_y_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
  217. \fI\fB
  218. \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
  219. \fI\fB
  220. \fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
  221. \fI\fB
  222. \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
  223. \fI\fB
  224. \fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
  225. \fI\fB
  226. \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
  227. \fI\fB
  228. \fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
  229. \fI\fB
  230. \fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
  231. \fI\fB
  232. \fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
  233. \fI\fB
  234. \fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, png_size_t \fIbuffer_size\fP\fB);\fP
  235. \fI\fB
  236. \fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
  237. \fI\fB
  238. \fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
  239. \fI\fB
  240. \fBvoid png_progressive_combine_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIold_row\fP\fB, png_bytep \fInew_row\fP\fB);\fP
  241. \fI\fB
  242. \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
  243. \fI\fB
  244. \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
  245. \fI\fB
  246. \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
  247. \fI\fB
  248. \fBvoid png_read_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
  249. \fI\fB
  250. \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
  251. \fI\fB
  252. \fBvoid png_read_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_bytepp \fP\fIdisplay_row\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
  253. \fI\fB
  254. \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
  255. \fI\fB
  256. \fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
  257. \fI\fB
  258. \fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
  259. \fI\fB
  260. \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
  261. \fI\fB
  262. \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
  263. \fI\fB
  264. \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
  265. \fI\fB
  266. \fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
  267. \fI\fB
  268. \fBvoid png_set_alpha_mode_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, png_fixed_point \fIoutput_gamma\fP\fB);\fP
  269. \fI\fB
  270. \fBvoid png_set_background (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, double \fIbackground_gamma\fP\fB);\fP
  271. \fI\fB
  272. \fBvoid png_set_background_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, png_uint_32 \fIbackground_gamma\fP\fB);\fP
  273. \fI\fB
  274. \fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
  275. \fI\fB
  276. \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
  277. \fI\fB
  278. \fBvoid png_set_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fIbackground\fP\fB);\fP
  279. \fI\fB
  280. \fBvoid png_set_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIwhite_x\fP\fB, double \fP\fIwhite_y\fP\fB, double \fP\fIred_x\fP\fB, double \fP\fIred_y\fP\fB, double \fP\fIgreen_x\fP\fB, double \fP\fIgreen_y\fP\fB, double \fP\fIblue_x\fP\fB, double \fIblue_y\fP\fB);\fP
  281. \fI\fB
  282. \fBvoid png_set_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwhite_x\fP\fB, png_uint_32 \fP\fIwhite_y\fP\fB, png_uint_32 \fP\fIred_x\fP\fB, png_uint_32 \fP\fIred_y\fP\fB, png_uint_32 \fP\fIgreen_x\fP\fB, png_uint_32 \fP\fIgreen_y\fP\fB, png_uint_32 \fP\fIblue_x\fP\fB, png_uint_32 \fIblue_y\fP\fB);\fP
  283. \fI\fB
  284. \fBvoid png_set_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIred_X\fP\fB, double \fP\fIred_Y\fP\fB, double \fP\fIred_Z\fP\fB, double \fP\fIgreen_X\fP\fB, double \fIgreen_Y,
  285. \fBdouble \fP\fIgreen_Z\fP\fB, double \fP\fIblue_X\fP\fB, double \fP\fIblue_Y\fP\fB, double \fIblue_Z\fP\fB);\fP
  286. \fI\fB
  287. \fBvoid png_set_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fIint_red_X\fP\fB, png_fixed_point \fP\fIint_red_Y\fP\fB, png_fixed_point \fP\fIint_red_Z\fP\fB, png_fixed_point \fP\fIint_green_X\fP\fB, png_fixed_point \fP\fIint_green_Y\fP\fB, png_fixed_point \fP\fIint_green_Z\fP\fB, png_fixed_point \fP\fIint_blue_X\fP\fB, png_fixed_point \fP\fIint_blue_Y\fP\fB, png_fixed_point \fIint_blue_Z\fP\fB);\fP
  288. \fI\fB
  289. \fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
  290. \fI\fB
  291. \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
  292. \fI\fB
  293. \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
  294. \fI\fB
  295. \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
  296. \fI\fB
  297. \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
  298. \fI\fB
  299. \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
  300. \fI\fB
  301. \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
  302. \fI\fB
  303. \fBvoid png_set_error_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarning_fn\fP\fB);\fP
  304. \fI\fB
  305. \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
  306. \fI\fB
  307. \fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
  308. \fI\fB
  309. \fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
  310. \fI\fB
  311. \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
  312. \fI\fB
  313. \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
  314. \fI\fB
  315. \fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
  316. \fI\fB
  317. \fBvoid png_set_filter_heuristics_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_fixed_point_p \fP\fIfilter_weights\fP\fB, png_fixed_point_p \fIfilter_costs\fP\fB);\fP
  318. \fI\fB
  319. \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
  320. \fI\fB
  321. \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
  322. \fI\fB
  323. \fBvoid png_set_gamma_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIscreen_gamma\fP\fB, png_uint_32 \fIdefault_file_gamma\fP\fB);\fP
  324. \fI\fB
  325. \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
  326. \fI\fB
  327. \fBvoid png_set_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIfile_gamma\fP\fB);\fP
  328. \fI\fB
  329. \fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
  330. \fI\fB
  331. \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
  332. \fI\fB
  333. \fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
  334. \fI\fB
  335. \fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_const_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_const_bytep \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
  336. \fI\fB
  337. \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
  338. \fI\fB
  339. \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
  340. \fI\fB
  341. \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
  342. \fI\fB
  343. \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
  344. \fI\fB
  345. \fBvoid png_set_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwidth\fP\fB, png_uint_32 \fP\fIheight\fP\fB, int \fP\fIbit_depth\fP\fB, int \fP\fIcolor_type\fP\fB, int \fP\fIinterlace_type\fP\fB, int \fP\fIcompression_type\fP\fB, int \fIfilter_type\fP\fB);\fP
  346. \fI\fB
  347. \fBvoid png_set_keep_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIkeep\fP\fB, png_bytep \fP\fIchunk_list\fP\fB, int \fInum_chunks\fP\fB);\fP
  348. \fI\fB
  349. \fBjmp_buf* png_set_longjmp_fn (png_structp \fP\fIpng_ptr\fP\fB, png_longjmp_ptr \fP\fIlongjmp_fn\fP\fB, size_t \fIjmp_buf_size\fP\fB);\fP
  350. \fI\fB
  351. \fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
  352. \fI\fB
  353. \fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
  354. \fI\fB
  355. \fBvoid png_set_mem_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
  356. \fI\fB
  357. \fBvoid png_set_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIoffset_x\fP\fB, png_uint_32 \fP\fIoffset_y\fP\fB, int \fIunit_type\fP\fB);\fP
  358. \fI\fB
  359. \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
  360. \fI\fB
  361. \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
  362. \fI\fB
  363. \fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
  364. \fI\fB
  365. \fBvoid png_set_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIpurpose\fP\fB, png_int_32 \fP\fIX0\fP\fB, png_int_32 \fP\fIX1\fP\fB, int \fP\fItype\fP\fB, int \fP\fInparams\fP\fB, png_charp \fP\fIunits\fP\fB, png_charpp \fIparams\fP\fB);\fP
  366. \fI\fB
  367. \fBvoid png_set_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIres_x\fP\fB, png_uint_32 \fP\fIres_y\fP\fB, int \fIunit_type\fP\fB);\fP
  368. \fI\fB
  369. \fBvoid png_set_progressive_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIprogressive_ptr\fP\fB, png_progressive_info_ptr \fP\fIinfo_fn\fP\fB, png_progressive_row_ptr \fP\fIrow_fn\fP\fB, png_progressive_end_ptr \fIend_fn\fP\fB);\fP
  370. \fI\fB
  371. \fBvoid png_set_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fInum_palette\fP\fB);\fP
  372. \fI\fB
  373. \fBvoid png_set_quantize (png_structp \fP\fIpng_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fP\fInum_palette\fP\fB, int \fP\fImaximum_colors\fP\fB, png_uint_16p \fP\fIhistogram\fP\fB, int \fIfull_quantize\fP\fB);\fP
  374. \fI\fB
  375. \fBvoid png_set_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fIread_data_fn\fP\fB);\fP
  376. \fI\fB
  377. \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
  378. \fI\fB
  379. \fBvoid png_set_read_user_chunk_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_chunk_ptr\fP\fB, png_user_chunk_ptr \fIread_user_chunk_fn\fP\fB);\fP
  380. \fI\fB
  381. \fBvoid png_set_read_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIread_user_transform_fn\fP\fB);\fP
  382. \fI\fB
  383. \fBvoid png_set_rgb_to_gray (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIerror_action\fP\fB, double \fP\fIred\fP\fB, double \fIgreen\fP\fB);\fP
  384. \fI\fB
  385. \fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_uint_32 \fP\fIred\fP\fB, png_uint_32 \fIgreen\fP\fB);\fP
  386. \fI\fB
  387. \fBvoid png_set_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytepp \fIrow_pointers\fP\fB);\fP
  388. \fI\fB
  389. \fBvoid png_set_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fIsig_bit\fP\fB);\fP
  390. \fI\fB
  391. \fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
  392. \fI\fB
  393. \fBvoid png_set_sCAL_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_fixed_point \fP\fIwidth\fP\fB, png_fixed_point \fIheight\fP\fB);\fP
  394. \fI\fB
  395. \fBvoid png_set_sCAL_s (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_charp \fP\fIwidth\fP\fB, png_charp \fIheight\fP\fB);\fP
  396. \fI\fB
  397. \fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
  398. \fI\fB
  399. \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
  400. \fI\fB
  401. \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
  402. \fI\fB
  403. \fBvoid png_set_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fP\fIsplt_ptr\fP\fB, int \fInum_spalettes\fP\fB);\fP
  404. \fI\fB
  405. \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
  406. \fI\fB
  407. \fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
  408. \fI\fB
  409. \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
  410. \fI\fB
  411. \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
  412. \fI\fB
  413. \fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
  414. \fI\fB
  415. \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
  416. \fI\fB
  417. \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
  418. \fI\fB
  419. \fBvoid png_set_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fItext_ptr\fP\fB, int \fInum_text\fP\fB);\fP
  420. \fI\fB
  421. \fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
  422. \fI\fB
  423. \fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
  424. \fI\fB
  425. \fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
  426. \fI\fB
  427. \fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
  428. \fI\fB
  429. \fBvoid \fP\fIpng_set_text_compression_method\fP\fB, (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod)\fP\fB);\fP
  430. \fI\fB
  431. \fBvoid png_set_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fImod_time\fP\fB);\fP
  432. \fI\fB
  433. \fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans_alpha\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_color\fP\fB);\fP
  434. \fI\fB
  435. \fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
  436. \fI\fB
  437. \fBpng_uint_32 png_set_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkp \fP\fIunknowns\fP\fB, int \fP\fInum\fP\fB, int \fIlocation\fP\fB);\fP
  438. \fI\fB
  439. \fBvoid png_set_unknown_chunk_location (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIchunk\fP\fB, int \fIlocation\fP\fB);\fP
  440. \fI\fB
  441. \fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
  442. \fI\fB
  443. \fBvoid png_set_user_transform_info (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_transform_ptr\fP\fB, int \fP\fIuser_transform_depth\fP\fB, int \fIuser_transform_channels\fP\fB);\fP
  444. \fI\fB
  445. \fBvoid png_set_write_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fP\fIwrite_data_fn\fP\fB, png_flush_ptr \fIoutput_flush_fn\fP\fB);\fP
  446. \fI\fB
  447. \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
  448. \fI\fB
  449. \fBvoid png_set_write_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIwrite_user_transform_fn\fP\fB);\fP
  450. \fI\fB
  451. \fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, png_size_t \fP\fIstart\fP\fB, png_size_t \fInum_to_check\fP\fB);\fP
  452. \fI\fB
  453. \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
  454. \fI\fB
  455. \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
  456. \fI\fB
  457. \fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
  458. \fI\fB
  459. \fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
  460. \fI\fB
  461. \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
  462. \fI\fB
  463. \fBvoid png_write_chunk_start (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_uint_32 \fIlength\fP\fB);\fP
  464. \fI\fB
  465. \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
  466. \fI\fB
  467. \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
  468. \fI\fB
  469. \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
  470. \fI\fB
  471. \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
  472. \fI\fB
  473. \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
  474. \fI\fB
  475. \fBvoid png_write_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
  476. \fI\fB
  477. \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
  478. \fI\fB
  479. \fBvoid png_write_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
  480. \fI\fB
  481. \fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
  482. \fI\fB
  483. \fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
  484. \fI\fB
  485. \fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
  486. \fI\fB
  487. .SH DESCRIPTION
  488. The
  489. .I libpng
  490. library supports encoding, decoding, and various manipulations of
  491. the Portable Network Graphics (PNG) format image files. It uses the
  492. .IR zlib(3)
  493. compression library.
  494. Following is a copy of the libpng-manual.txt file that accompanies libpng.
  495. .SH LIBPNG.TXT
  496. libpng-manual.txt - A description on how to use and modify libpng
  497. libpng version 1.5.9 - February 18, 2012
  498. Updated and distributed by Glenn Randers-Pehrson
  499. <glennrp at users.sourceforge.net>
  500. Copyright (c) 1998-2011 Glenn Randers-Pehrson
  501. This document is released under the libpng license.
  502. For conditions of distribution and use, see the disclaimer
  503. and license in png.h
  504. Based on:
  505. libpng versions 0.97, January 1998, through 1.5.9 - February 18, 2012
  506. Updated and distributed by Glenn Randers-Pehrson
  507. Copyright (c) 1998-2011 Glenn Randers-Pehrson
  508. libpng 1.0 beta 6 version 0.96 May 28, 1997
  509. Updated and distributed by Andreas Dilger
  510. Copyright (c) 1996, 1997 Andreas Dilger
  511. libpng 1.0 beta 2 - version 0.88 January 26, 1996
  512. For conditions of distribution and use, see copyright
  513. notice in png.h. Copyright (c) 1995, 1996 Guy Eric
  514. Schalnat, Group 42, Inc.
  515. Updated/rewritten per request in the libpng FAQ
  516. Copyright (c) 1995, 1996 Frank J. T. Wojcik
  517. December 18, 1995 & January 20, 1996
  518. .SH I. Introduction
  519. This file describes how to use and modify the PNG reference library
  520. (known as libpng) for your own use. There are five sections to this
  521. file: introduction, structures, reading, writing, and modification and
  522. configuration notes for various special platforms. In addition to this
  523. file, example.c is a good starting point for using the library, as
  524. it is heavily commented and should include everything most people
  525. will need. We assume that libpng is already installed; see the
  526. INSTALL file for instructions on how to install libpng.
  527. For examples of libpng usage, see the files "example.c", "pngtest.c",
  528. and the files in the "contrib" directory, all of which are included in
  529. the libpng distribution.
  530. Libpng was written as a companion to the PNG specification, as a way
  531. of reducing the amount of time and effort it takes to support the PNG
  532. file format in application programs.
  533. The PNG specification (second edition), November 2003, is available as
  534. a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
  535. <http://www.w3.org/TR/2003/REC-PNG-20031110/
  536. The W3C and ISO documents have identical technical content.
  537. The PNG-1.2 specification is available at
  538. <http://www.libpng.org/pub/png/documents/>. It is technically equivalent
  539. to the PNG specification (second edition) but has some additional material.
  540. The PNG-1.0 specification is available
  541. as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
  542. W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
  543. Some additional chunks are described in the special-purpose public chunks
  544. documents at <http://www.libpng.org/pub/png/documents/>.
  545. Other information
  546. about PNG, and the latest version of libpng, can be found at the PNG home
  547. page, <http://www.libpng.org/pub/png/>.
  548. Most users will not have to modify the library significantly; advanced
  549. users may want to modify it more. All attempts were made to make it as
  550. complete as possible, while keeping the code easy to understand.
  551. Currently, this library only supports C. Support for other languages
  552. is being considered.
  553. Libpng has been designed to handle multiple sessions at one time,
  554. to be easily modifiable, to be portable to the vast majority of
  555. machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
  556. to use. The ultimate goal of libpng is to promote the acceptance of
  557. the PNG file format in whatever way possible. While there is still
  558. work to be done (see the TODO file), libpng should cover the
  559. majority of the needs of its users.
  560. Libpng uses zlib for its compression and decompression of PNG files.
  561. Further information about zlib, and the latest version of zlib, can
  562. be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
  563. The zlib compression utility is a general purpose utility that is
  564. useful for more than PNG files, and can be used without libpng.
  565. See the documentation delivered with zlib for more details.
  566. You can usually find the source files for the zlib utility wherever you
  567. find the libpng source files.
  568. Libpng is thread safe, provided the threads are using different
  569. instances of the structures. Each thread should have its own
  570. png_struct and png_info instances, and thus its own image.
  571. Libpng does not protect itself against two threads using the
  572. same instance of a structure.
  573. .SH II. Structures
  574. There are two main structures that are important to libpng, png_struct
  575. and png_info. Both are internal structures that are no longer exposed
  576. in the libpng interface (as of libpng 1.5.0).
  577. The png_info structure is designed to provide information about the
  578. PNG file. At one time, the fields of png_info were intended to be
  579. directly accessible to the user. However, this tended to cause problems
  580. with applications using dynamically loaded libraries, and as a result
  581. a set of interface functions for png_info (the png_get_*() and png_set_*()
  582. functions) was developed, and direct access to the png_info fields was
  583. deprecated..
  584. The png_struct structure is the object used by the library to decode a
  585. single image. As of 1.5.0 this structure is also not exposed.
  586. Almost all libpng APIs require a pointer to a png_struct as the first argument.
  587. Many (in particular the png_set and png_get APIs) also require a pointer
  588. to png_info as the second argument. Some application visible macros
  589. defined in png.h designed for basic data access (reading and writing
  590. integers in the PNG format) don't take a png_info pointer, but it's almost
  591. always safe to assume that a (png_struct*) has to be passed to call an API
  592. function.
  593. You can have more than one png_info structure associated with an image,
  594. as illustrated in pngtest.c, one for information valid prior to the
  595. IDAT chunks and another (called "end_info" below) for things after them.
  596. The png.h header file is an invaluable reference for programming with libpng.
  597. And while I'm on the topic, make sure you include the libpng header file:
  598. #include <png.h>
  599. and also (as of libpng-1.5.0) the zlib header file, if you need it:
  600. #include <zlib.h>
  601. .SS Types
  602. The png.h header file defines a number of integral types used by the
  603. APIs. Most of these are fairly obvious; for example types corresponding
  604. to integers of particular sizes and types for passing color values.
  605. One exception is how non-integral numbers are handled. For application
  606. convenience most APIs that take such numbers have C (double) arguments,
  607. however internally PNG, and libpng, use 32 bit signed integers and encode
  608. the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
  609. macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
  610. which is simply (png_int_32).
  611. All APIs that take (double) arguments also have a matching API that
  612. takes the corresponding fixed point integer arguments. The fixed point
  613. API has the same name as the floating point one with "_fixed" appended.
  614. The actual range of values permitted in the APIs is frequently less than
  615. the full range of (png_fixed_point) (-21474 to +21474). When APIs require
  616. a non-negative argument the type is recorded as png_uint_32 above. Consult
  617. the header file and the text below for more information.
  618. Special care must be take with sCAL chunk handling because the chunk itself
  619. uses non-integral values encoded as strings containing decimal floating point
  620. numbers. See the comments in the header file.
  621. .SS Configuration
  622. The main header file function declarations are frequently protected by C
  623. preprocessing directives of the form:
  624. #ifdef PNG_feature_SUPPORTED
  625. declare-function
  626. #endif
  627. ...
  628. #ifdef PNG_feature_SUPPORTED
  629. use-function
  630. #endif
  631. The library can be built without support for these APIs, although a
  632. standard build will have all implemented APIs. Application programs
  633. should check the feature macros before using an API for maximum
  634. portability. From libpng 1.5.0 the feature macros set during the build
  635. of libpng are recorded in the header file "pnglibconf.h" and this file
  636. is always included by png.h.
  637. If you don't need to change the library configuration from the default, skip to
  638. the next section ("Reading").
  639. Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
  640. of the build project files in the 'projects' directory simply copy
  641. scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
  642. systems do not permit easy auto-configuration of the library - they only
  643. support the default configuration.
  644. The easiest way to make minor changes to the libpng configuration when
  645. auto-configuration is supported is to add definitions to the command line
  646. using (typically) CPPFLAGS. For example:
  647. CPPFLAGS=-DPNG_NO_FLOATING_ARITHMETIC
  648. will change the internal libpng math implementation for gamma correction and
  649. other arithmetic calculations to fixed point, avoiding the need for fast
  650. floating point support. The result can be seen in the generated pnglibconf.h -
  651. make sure it contains the changed feature macro setting.
  652. If you need to make more extensive configuration changes - more than one or two
  653. feature macro settings - you can either add -DPNG_USER_CONFIG to the build
  654. command line and put a list of feature macro settings in pngusr.h or you can set
  655. DFA_XTRA (a makefile variable) to a file containing the same information in the
  656. form of 'option' settings.
  657. A. Changing pnglibconf.h
  658. A variety of methods exist to build libpng. Not all of these support
  659. reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
  660. rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
  661. Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
  662. pnglibconf.h and changing the lines defining the supported features, paying
  663. very close attention to the 'option' information in scripts/pnglibconf.dfa
  664. that describes those features and their requirements. This is easy to get
  665. wrong.
  666. B. Configuration using DFA_XTRA
  667. Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
  668. variant such as 'nawk' or 'gawk', is available. The configure build will
  669. automatically find an appropriate awk and build pnglibconf.h.
  670. The scripts/pnglibconf.mak file contains a set of make rules for doing the
  671. same thing if configure is not used, and many of the makefiles in the scripts
  672. directory use this approach.
  673. When rebuilding simply write a new file containing changed options and set
  674. DFA_XTRA to the name of this file. This causes the build to append the new file
  675. to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
  676. of the following forms:
  677. everything = off
  678. This turns all optional features off. Include it at the start of pngusr.dfa to
  679. make it easier to build a minimal configuration. You will need to turn at least
  680. some features on afterward to enable either reading or writing code, or both.
  681. option feature on
  682. option feature off
  683. Enable or disable a single feature. This will automatically enable other
  684. features required by a feature that is turned on or disable other features that
  685. require a feature which is turned off. Conflicting settings will cause an error
  686. message to be emitted by awk.
  687. setting feature default value
  688. Changes the default value of setting 'feature' to 'value'. There are a small
  689. number of settings listed at the top of pnglibconf.h, they are documented in the
  690. source code. Most of these values have performance implications for the library
  691. but most of them have no visible effect on the API. Some can also be overridden
  692. from the API.
  693. This method of building a customized pnglibconf.h is illustrated in
  694. contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
  695. pngusr.dfa in these directories.
  696. C. Configuration using PNG_USR_CONFIG
  697. If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the file
  698. pngusr.h will automatically be included before the options in
  699. scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
  700. macro definitions turning features on or off or setting settings.
  701. Apart from the global setting "everything = off" all the options listed above
  702. can be set using macros in pngusr.h:
  703. #define PNG_feature_SUPPORTED
  704. is equivalent to:
  705. option feature on
  706. #define PNG_NO_feature
  707. is equivalent to:
  708. option feature off
  709. #define PNG_feature value
  710. is equivalent to:
  711. setting feature default value
  712. Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
  713. pngusr file you supply override the contents of scripts/pnglibconf.dfa
  714. If confusing or incomprehensible behavior results it is possible to
  715. examine the intermediate file pnglibconf.dfn to find the full set of
  716. dependency information for each setting and option. Simply locate the
  717. feature in the file and read the C comments that precede it.
  718. This method is also illustrated in the contrib/pngminim/* makefiles and
  719. pngusr.h.
  720. .SH III. Reading
  721. We'll now walk you through the possible functions to call when reading
  722. in a PNG file sequentially, briefly explaining the syntax and purpose
  723. of each one. See example.c and png.h for more detail. While
  724. progressive reading is covered in the next section, you will still
  725. need some of the functions discussed in this section to read a PNG
  726. file.
  727. .SS Setup
  728. You will want to do the I/O initialization(*) before you get into libpng,
  729. so if it doesn't work, you don't have much to undo. Of course, you
  730. will also want to insure that you are, in fact, dealing with a PNG
  731. file. Libpng provides a simple check to see if a file is a PNG file.
  732. To use it, pass in the first 1 to 8 bytes of the file to the function
  733. png_sig_cmp(), and it will return 0 (false) if the bytes match the
  734. corresponding bytes of the PNG signature, or nonzero (true) otherwise.
  735. Of course, the more bytes you pass in, the greater the accuracy of the
  736. prediction.
  737. If you are intending to keep the file pointer open for use in libpng,
  738. you must ensure you don't read more than 8 bytes from the beginning
  739. of the file, and you also have to make a call to png_set_sig_bytes_read()
  740. with the number of bytes you read from the beginning. Libpng will
  741. then only check the bytes (if any) that your program didn't read.
  742. (*): If you are not using the standard I/O functions, you will need
  743. to replace them with custom functions. See the discussion under
  744. Customizing libpng.
  745. FILE *fp = fopen(file_name, "rb");
  746. if (!fp)
  747. {
  748. return (ERROR);
  749. }
  750. fread(header, 1, number, fp);
  751. is_png = !png_sig_cmp(header, 0, number);
  752. if (!is_png)
  753. {
  754. return (NOT_PNG);
  755. }
  756. Next, png_struct and png_info need to be allocated and initialized. In
  757. order to ensure that the size of these structures is correct even with a
  758. dynamically linked libpng, there are functions to initialize and
  759. allocate the structures. We also pass the library version, optional
  760. pointers to error handling functions, and a pointer to a data struct for
  761. use by the error functions, if necessary (the pointer and functions can
  762. be NULL if the default error handlers are to be used). See the section
  763. on Changes to Libpng below regarding the old initialization functions.
  764. The structure allocation functions quietly return NULL if they fail to
  765. create the structure, so your application should check for that.
  766. png_structp png_ptr = png_create_read_struct
  767. (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
  768. user_error_fn, user_warning_fn);
  769. if (!png_ptr)
  770. return (ERROR);
  771. png_infop info_ptr = png_create_info_struct(png_ptr);
  772. if (!info_ptr)
  773. {
  774. png_destroy_read_struct(&png_ptr,
  775. (png_infopp)NULL, (png_infopp)NULL);
  776. return (ERROR);
  777. }
  778. If you want to use your own memory allocation routines,
  779. use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
  780. png_create_read_struct_2() instead of png_create_read_struct():
  781. png_structp png_ptr = png_create_read_struct_2
  782. (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
  783. user_error_fn, user_warning_fn, (png_voidp)
  784. user_mem_ptr, user_malloc_fn, user_free_fn);
  785. The error handling routines passed to png_create_read_struct()
  786. and the memory alloc/free routines passed to png_create_struct_2()
  787. are only necessary if you are not using the libpng supplied error
  788. handling and memory alloc/free functions.
  789. When libpng encounters an error, it expects to longjmp back
  790. to your routine. Therefore, you will need to call setjmp and pass
  791. your png_jmpbuf(png_ptr). If you read the file from different
  792. routines, you will need to update the longjmp buffer every time you enter
  793. a new routine that will call a png_*() function.
  794. See your documentation of setjmp/longjmp for your compiler for more
  795. information on setjmp/longjmp. See the discussion on libpng error
  796. handling in the Customizing Libpng section below for more information
  797. on the libpng error handling. If an error occurs, and libpng longjmp's
  798. back to your setjmp, you will want to call png_destroy_read_struct() to
  799. free any memory.
  800. if (setjmp(png_jmpbuf(png_ptr)))
  801. {
  802. png_destroy_read_struct(&png_ptr, &info_ptr,
  803. &end_info);
  804. fclose(fp);
  805. return (ERROR);
  806. }
  807. Pass (png_infopp)NULL instead of &end_info if you didn't create
  808. an end_info structure.
  809. If you would rather avoid the complexity of setjmp/longjmp issues,
  810. you can compile libpng with PNG_NO_SETJMP, in which case
  811. errors will result in a call to PNG_ABORT() which defaults to abort().
  812. You can #define PNG_ABORT() to a function that does something
  813. more useful than abort(), as long as your function does not
  814. return.
  815. Now you need to set up the input code. The default for libpng is to
  816. use the C function fread(). If you use this, you will need to pass a
  817. valid FILE * in the function png_init_io(). Be sure that the file is
  818. opened in binary mode. If you wish to handle reading data in another
  819. way, you need not call the png_init_io() function, but you must then
  820. implement the libpng I/O methods discussed in the Customizing Libpng
  821. section below.
  822. png_init_io(png_ptr, fp);
  823. If you had previously opened the file and read any of the signature from
  824. the beginning in order to see if this was a PNG file, you need to let
  825. libpng know that there are some bytes missing from the start of the file.
  826. png_set_sig_bytes(png_ptr, number);
  827. You can change the zlib compression buffer size to be used while
  828. reading compressed data with
  829. png_set_compression_buffer_size(png_ptr, buffer_size);
  830. where the default size is 8192 bytes. Note that the buffer size
  831. is changed immediately and the buffer is reallocated immediately,
  832. instead of setting a flag to be acted upon later.
  833. If you want CRC errors to be handled in a different manner than
  834. the default, use
  835. png_set_crc_action(png_ptr, crit_action, ancil_action);
  836. The values for png_set_crc_action() say how libpng is to handle CRC errors in
  837. ancillary and critical chunks, and whether to use the data contained
  838. therein. Note that it is impossible to "discard" data in a critical
  839. chunk.
  840. Choices for (int) crit_action are
  841. PNG_CRC_DEFAULT 0 error/quit
  842. PNG_CRC_ERROR_QUIT 1 error/quit
  843. PNG_CRC_WARN_USE 3 warn/use data
  844. PNG_CRC_QUIET_USE 4 quiet/use data
  845. PNG_CRC_NO_CHANGE 5 use the current value
  846. Choices for (int) ancil_action are
  847. PNG_CRC_DEFAULT 0 error/quit
  848. PNG_CRC_ERROR_QUIT 1 error/quit
  849. PNG_CRC_WARN_DISCARD 2 warn/discard data
  850. PNG_CRC_WARN_USE 3 warn/use data
  851. PNG_CRC_QUIET_USE 4 quiet/use data
  852. PNG_CRC_NO_CHANGE 5 use the current value
  853. .SS Setting up callback code
  854. You can set up a callback function to handle any unknown chunks in the
  855. input stream. You must supply the function
  856. read_chunk_callback(png_structp png_ptr,
  857. png_unknown_chunkp chunk);
  858. {
  859. /* The unknown chunk structure contains your
  860. chunk data, along with similar data for any other
  861. unknown chunks: */
  862. png_byte name[5];
  863. png_byte *data;
  864. png_size_t size;
  865. /* Note that libpng has already taken care of
  866. the CRC handling */
  867. /* put your code here. Search for your chunk in the
  868. unknown chunk structure, process it, and return one
  869. of the following: */
  870. return (-n); /* chunk had an error */
  871. return (0); /* did not recognize */
  872. return (n); /* success */
  873. }
  874. (You can give your function another name that you like instead of
  875. "read_chunk_callback")
  876. To inform libpng about your function, use
  877. png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
  878. read_chunk_callback);
  879. This names not only the callback function, but also a user pointer that
  880. you can retrieve with
  881. png_get_user_chunk_ptr(png_ptr);
  882. If you call the png_set_read_user_chunk_fn() function, then all unknown
  883. chunks will be saved when read, in case your callback function will need
  884. one or more of them. This behavior can be changed with the
  885. png_set_keep_unknown_chunks() function, described below.
  886. At this point, you can set up a callback function that will be
  887. called after each row has been read, which you can use to control
  888. a progress meter or the like. It's demonstrated in pngtest.c.
  889. You must supply a function
  890. void read_row_callback(png_structp png_ptr,
  891. png_uint_32 row, int pass);
  892. {
  893. /* put your code here */
  894. }
  895. (You can give it another name that you like instead of "read_row_callback")
  896. To inform libpng about your function, use
  897. png_set_read_status_fn(png_ptr, read_row_callback);
  898. When this function is called the row has already been completely processed and
  899. the 'row' and 'pass' refer to the next row to be handled. For the
  900. non-interlaced case the row that was just handled is simply one less than the
  901. passed in row number, and pass will always be 0. For the interlaced case the
  902. same applies unless the row value is 0, in which case the row just handled was
  903. the last one from one of the preceding passes. Because interlacing may skip a
  904. pass you cannot be sure that the preceding pass is just 'pass-1', if you really
  905. need to know what the last pass is record (row,pass) from the callback and use
  906. the last recorded value each time.
  907. As with the user transform you can find the output row using the
  908. PNG_ROW_FROM_PASS_ROW macro.
  909. .SS Unknown-chunk handling
  910. Now you get to set the way the library processes unknown chunks in the
  911. input PNG stream. Both known and unknown chunks will be read. Normal
  912. behavior is that known chunks will be parsed into information in
  913. various info_ptr members while unknown chunks will be discarded. This
  914. behavior can be wasteful if your application will never use some known
  915. chunk types. To change this, you can call:
  916. png_set_keep_unknown_chunks(png_ptr, keep,
  917. chunk_list, num_chunks);
  918. keep - 0: default unknown chunk handling
  919. 1: ignore; do not keep
  920. 2: keep only if safe-to-copy
  921. 3: keep even if unsafe-to-copy
  922. You can use these definitions:
  923. PNG_HANDLE_CHUNK_AS_DEFAULT 0
  924. PNG_HANDLE_CHUNK_NEVER 1
  925. PNG_HANDLE_CHUNK_IF_SAFE 2
  926. PNG_HANDLE_CHUNK_ALWAYS 3
  927. chunk_list - list of chunks affected (a byte string,
  928. five bytes per chunk, NULL or '\0' if
  929. num_chunks is 0)
  930. num_chunks - number of chunks affected; if 0, all
  931. unknown chunks are affected. If nonzero,
  932. only the chunks in the list are affected
  933. Unknown chunks declared in this way will be saved as raw data onto a
  934. list of png_unknown_chunk structures. If a chunk that is normally
  935. known to libpng is named in the list, it will be handled as unknown,
  936. according to the "keep" directive. If a chunk is named in successive
  937. instances of png_set_keep_unknown_chunks(), the final instance will
  938. take precedence. The IHDR and IEND chunks should not be named in
  939. chunk_list; if they are, libpng will process them normally anyway.
  940. If you know that your application will never make use of some particular
  941. chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
  942. Here is an example of the usage of png_set_keep_unknown_chunks(),
  943. where the private "vpAg" chunk will later be processed by a user chunk
  944. callback function:
  945. png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
  946. #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
  947. png_byte unused_chunks[]=
  948. {
  949. 104, 73, 83, 84, (png_byte) '\0', /* hIST */
  950. 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
  951. 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
  952. 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
  953. 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
  954. 116, 73, 77, 69, (png_byte) '\0', /* tIME */
  955. };
  956. #endif
  957. ...
  958. #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
  959. /* ignore all unknown chunks: */
  960. png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
  961. /* except for vpAg: */
  962. png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
  963. /* also ignore unused known chunks: */
  964. png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
  965. (int)sizeof(unused_chunks)/5);
  966. #endif
  967. .SS User limits
  968. The PNG specification allows the width and height of an image to be as
  969. large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
  970. Since very few applications really need to process such large images,
  971. we have imposed an arbitrary 1-million limit on rows and columns.
  972. Larger images will be rejected immediately with a png_error() call. If
  973. you wish to change this limit, you can use
  974. png_set_user_limits(png_ptr, width_max, height_max);
  975. to set your own limits, or use width_max = height_max = 0x7fffffffL
  976. to allow all valid dimensions (libpng may reject some very large images
  977. anyway because of potential buffer overflow conditions).
  978. You should put this statement after you create the PNG structure and
  979. before calling png_read_info(), png_read_png(), or png_process_data().
  980. When writing a PNG datastream, put this statement before calling
  981. png_write_info() or png_write_png().
  982. If you need to retrieve the limits that are being applied, use
  983. width_max = png_get_user_width_max(png_ptr);
  984. height_max = png_get_user_height_max(png_ptr);
  985. The PNG specification sets no limit on the number of ancillary chunks
  986. allowed in a PNG datastream. You can impose a limit on the total number
  987. of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
  988. png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
  989. where 0x7fffffffL means unlimited. You can retrieve this limit with
  990. chunk_cache_max = png_get_chunk_cache_max(png_ptr);
  991. This limit also applies to the number of buffers that can be allocated
  992. by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks.
  993. You can also set a limit on the amount of memory that a compressed chunk
  994. other than IDAT can occupy, with
  995. png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
  996. and you can retrieve the limit with
  997. chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
  998. Any chunks that would cause either of these limits to be exceeded will
  999. be ignored.
  1000. .SS Information about your system
  1001. If you intend to display the PNG or to incorporate it in other image data you
  1002. need to tell libpng information about your display or drawing surface so that
  1003. libpng can convert the values in the image to match the display.
  1004. From libpng-1.5.4 this information can be set before reading the PNG file
  1005. header. In earlier versions png_set_gamma() existed but behaved incorrectly if
  1006. called before the PNG file header had been read and png_set_alpha_mode() did not
  1007. exist.
  1008. If you need to support versions prior to libpng-1.5.4 test the version number
  1009. as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
  1010. described in the appropriate manual page.
  1011. You give libpng the encoding expected by your system expressed as a 'gamma'
  1012. value. You can also specify a default encoding for the PNG file in
  1013. case the required information is missing from the file. By default libpng
  1014. assumes that the PNG data matches your system, to keep this default call:
  1015. png_set_gamma(png_ptr, screen_gamma, 1/screen_gamma/*file gamma*/);
  1016. or you can use the fixed point equivalent:
  1017. png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma, PNG_FP_1/screen_gamma);
  1018. If you don't know the gamma for your system it is probably 2.2 - a good
  1019. approximation to the IEC standard for display systems (sRGB). If images are
  1020. too contrasty or washed out you got the value wrong - check your system
  1021. documentation!
  1022. Many systems permit the system gamma to be changed via a lookup table in the
  1023. display driver, a few systems, including older Macs, change the response by
  1024. default. As of 1.5.4 three special values are available to handle common
  1025. situations:
  1026. PNG_DEFAULT_sRGB: Indicates that the system conforms to the IEC 61966-2-1
  1027. standard. This matches almost all systems.
  1028. PNG_GAMMA_MAC_18: Indicates that the system is an older (pre Mac OS 10.6)
  1029. Apple Macintosh system with the default settings.
  1030. PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates that the
  1031. system expects data with no gamma encoding.
  1032. You would use the linear (unencoded) value if you need to process the pixel
  1033. values further because this avoids the need to decode and reencode each
  1034. component value whenever arithmetic is performed. A lot of graphics software
  1035. uses linear values for this reason, often with higher precision component values
  1036. to preserve overall accuracy.
  1037. The second thing you may need to tell libpng about is how your system handles
  1038. alpha channel information. Some, but not all, PNG files contain an alpha
  1039. channel. To display these files correctly you need to compose the data onto a
  1040. suitable background, as described in the PNG specification.
  1041. Libpng only supports composing onto a single color (using png_set_background;
  1042. see below). Otherwise you must do the composition yourself and, in this case,
  1043. you may need to call png_set_alpha_mode:
  1044. #if PNG_LIBPNG_VER >= 10504
  1045. png_set_alpha_mode(png_ptr, mode, screen_gamma);
  1046. #else
  1047. png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
  1048. #endif
  1049. The screen_gamma value is the same as the argument to png_set_gamma; however,
  1050. how it affects the output depends on the mode. png_set_alpha_mode() sets the
  1051. file gamma default to 1/screen_gamma, so normally you don't need to call
  1052. png_set_gamma. If you need different defaults call png_set_gamma() before
  1053. png_set_alpha_mode() - if you call it after it will override the settings made
  1054. by png_set_alpha_mode().
  1055. The mode is as follows:
  1056. PNG_ALPHA_PNG: The data is encoded according to the PNG specification. Red,
  1057. green and blue, or gray, components are gamma encoded color
  1058. values and are not premultiplied by the alpha value. The
  1059. alpha value is a linear measure of the contribution of the
  1060. pixel to the corresponding final output pixel.
  1061. You should normally use this format if you intend to perform
  1062. color correction on the color values; most, maybe all, color
  1063. correction software has no handling for the alpha channel and,
  1064. anyway, the math to handle pre-multiplied component values is
  1065. unnecessarily complex.
  1066. Before you do any arithmetic on the component values you need
  1067. to remove the gamma encoding and multiply out the alpha
  1068. channel. See the PNG specification for more detail. It is
  1069. important to note that when an image with an alpha channel is
  1070. scaled, linear encoded, pre-multiplied component values must
  1071. be used!
  1072. The remaining modes assume you don't need to do any further color correction or
  1073. that if you do, your color correction software knows all about alpha (it
  1074. probably doesn't!)
  1075. PNG_ALPHA_STANDARD: The data libpng produces
  1076. is encoded in the standard way
  1077. assumed by most correctly written graphics software.
  1078. The gamma encoding will be removed by libpng and the
  1079. linear component values will be pre-multiplied by the
  1080. alpha channel.
  1081. With this format the final image must be re-encoded to
  1082. match the display gamma before the image is displayed.
  1083. If your system doesn't do that, yet still seems to
  1084. perform arithmetic on the pixels without decoding them,
  1085. it is broken - check out the modes below.
  1086. With PNG_ALPHA_STANDARD libpng always produces linear
  1087. component values, whatever screen_gamma you supply. The
  1088. screen_gamma value is, however, used as a default for
  1089. the file gamma if the PNG file has no gamma information.
  1090. If you call png_set_gamma() after png_set_alpha_mode() you
  1091. will override the linear encoding. Instead the
  1092. pre-multiplied pixel values will be gamma encoded but
  1093. the alpha channel will still be linear. This may
  1094. actually match the requirements of some broken software,
  1095. but it is unlikely.
  1096. While linear 8-bit data is often used it has
  1097. insufficient precision for any image with a reasonable
  1098. dynamic range. To avoid problems, and if your software
  1099. supports it, use png_set_expand_16() to force all
  1100. components to 16 bits.
  1101. PNG_ALPHA_OPTIMIZED: This mode is the same
  1102. as PNG_ALPHA_STANDARD except that
  1103. completely opaque pixels are gamma encoded according to
  1104. the screen_gamma value. Pixels with alpha less than 1.0
  1105. will still have linear components.
  1106. Use this format if you have control over your
  1107. compositing software and do don't do other arithmetic
  1108. (such as scaling) on the data you get from libpng. Your
  1109. compositing software can simply copy opaque pixels to
  1110. the output but still has linear values for the
  1111. non-opaque pixels.
  1112. In normal compositing, where the alpha channel encodes
  1113. partial pixel coverage (as opposed to broad area
  1114. translucency), the inaccuracies of the 8-bit
  1115. representation of non-opaque pixels are irrelevant.
  1116. You can also try this format if your software is broken;
  1117. it might look better.
  1118. PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD;
  1119. however, all component values,
  1120. including the alpha channel are gamma encoded. This is
  1121. an appropriate format to try if your software, or more
  1122. likely hardware, is totally broken, i.e., if it performs
  1123. linear arithmetic directly on gamma encoded values.
  1124. In most cases of broken software or hardware the bug in the final display
  1125. manifests as a subtle halo around composited parts of the image. You may not
  1126. even perceive this as a halo; the composited part of the image may simply appear
  1127. separate from the background, as though it had been cut out of paper and pasted
  1128. on afterward.
  1129. If you don't have to deal with bugs in software or hardware, or if you can fix
  1130. them, there are three recommended ways of using png_set_alpha_mode():
  1131. png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
  1132. screen_gamma);
  1133. You can do color correction on the result (libpng does not currently
  1134. support color correction internally). When you handle the alpha channel
  1135. you need to undo the gamma encoding and multiply out the alpha.
  1136. png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
  1137. screen_gamma);
  1138. png_set_expand_16(png_ptr);
  1139. If you are using the high level interface, don't call png_set_expand_16();
  1140. instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
  1141. With this mode you can't do color correction, but you can do arithmetic,
  1142. including composition and scaling, on the data without further processing.
  1143. png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
  1144. screen_gamma);
  1145. You can avoid the expansion to 16-bit components with this mode, but you
  1146. lose the ability to scale the image or perform other linear arithmetic.
  1147. All you can do is compose the result onto a matching output. Since this
  1148. mode is libpng-specific you also need to write your own composition
  1149. software.
  1150. If you don't need, or can't handle, the alpha channel you can call
  1151. png_set_background() to remove it by compositing against a fixed color. Don't
  1152. call png_set_strip_alpha() to do this - it will leave spurious pixel values in
  1153. transparent parts of this image.
  1154. png_set_background(png_ptr, &background_color,
  1155. PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
  1156. The background_color is an RGB or grayscale value according to the data format
  1157. libpng will produce for you. Because you don't yet know the format of the PNG
  1158. file, if you call png_set_background at this point you must arrange for the
  1159. format produced by libpng to always have 8-bit or 16-bit components and then
  1160. store the color as an 8-bit or 16-bit color as appropriate. The color contains
  1161. separate gray and RGB component values, so you can let libpng produce gray or
  1162. RGB output according to the input format, but low bit depth grayscale images
  1163. must always be converted to at least 8-bit format. (Even though low bit depth
  1164. grayscale images can't have an alpha channel they can have a transparent
  1165. color!)
  1166. You set the transforms you need later, either as flags to the high level
  1167. interface or libpng API calls for the low level interface. For reference the
  1168. settings and API calls required are:
  1169. 8-bit values:
  1170. PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
  1171. png_set_expand(png_ptr); png_set_scale_16(png_ptr);
  1172. If you must get exactly the same inaccurate results
  1173. produced by default in versions prior to libpng-1.5.4,
  1174. use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
  1175. instead.
  1176. 16-bit values:
  1177. PNG_TRANSFORM_EXPAND_16
  1178. png_set_expand_16(png_ptr);
  1179. In either case palette image data will be expanded to RGB. If you just want
  1180. color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
  1181. to the list.
  1182. Calling png_set_background before the PNG file header is read will not work
  1183. prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
  1184. errors it is therefore much safer to call png_set_background after the head has
  1185. been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
  1186. used with the high level interface.
  1187. .SS The high-level read interface
  1188. At this point there are two ways to proceed; through the high-level
  1189. read interface, or through a sequence of low-level read operations.
  1190. You can use the high-level interface if (a) you are willing to read
  1191. the entire image into memory, and (b) the input transformations
  1192. you want to do are limited to the following set:
  1193. PNG_TRANSFORM_IDENTITY No transformation
  1194. PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
  1195. 8-bit accurately
  1196. PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
  1197. 8-bit less accurately
  1198. PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
  1199. PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
  1200. samples to bytes
  1201. PNG_TRANSFORM_PACKSWAP Change order of packed
  1202. pixels to LSB first
  1203. PNG_TRANSFORM_EXPAND Perform set_expand()
  1204. PNG_TRANSFORM_INVERT_MONO Invert monochrome images
  1205. PNG_TRANSFORM_SHIFT Normalize pixels to the
  1206. sBIT depth
  1207. PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
  1208. to BGRA
  1209. PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
  1210. to AG
  1211. PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
  1212. to transparency
  1213. PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
  1214. PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
  1215. to RGB (or GA to RGBA)
  1216. PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
  1217. (This excludes setting a background color, doing gamma transformation,
  1218. quantizing, and setting filler.) If this is the case, simply do this:
  1219. png_read_png(png_ptr, info_ptr, png_transforms, NULL)
  1220. where png_transforms is an integer containing the bitwise OR of some
  1221. set of transformation flags. This call is equivalent to png_read_info(),
  1222. followed the set of transformations indicated by the transform mask,
  1223. then png_read_image(), and finally png_read_end().
  1224. (The final parameter of this call is not yet used. Someday it might point
  1225. to transformation parameters required by some future input transform.)
  1226. You must use png_transforms and not call any png_set_transform() functions
  1227. when you use png_read_png().
  1228. After you have called png_read_png(), you can retrieve the image data
  1229. with
  1230. row_pointers = png_get_rows(png_ptr, info_ptr);
  1231. where row_pointers is an array of pointers to the pixel data for each row:
  1232. png_bytep row_pointers[height];
  1233. If you know your image size and pixel size ahead of time, you can allocate
  1234. row_pointers prior to calling png_read_png() with
  1235. if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
  1236. png_error (png_ptr,
  1237. "Image is too tall to process in memory");
  1238. if (width > PNG_UINT_32_MAX/pixel_size)
  1239. png_error (png_ptr,
  1240. "Image is too wide to process in memory");
  1241. row_pointers = png_malloc(png_ptr,
  1242. height*png_sizeof(png_bytep));
  1243. for (int i=0; i<height, i++)
  1244. row_pointers[i]=NULL; /* security precaution */
  1245. for (int i=0; i<height, i++)
  1246. row_pointers[i]=png_malloc(png_ptr,
  1247. width*pixel_size);
  1248. png_set_rows(png_ptr, info_ptr, &row_pointers);
  1249. Alternatively you could allocate your image in one big block and define
  1250. row_pointers[i] to point into the proper places in your block.
  1251. If you use png_set_rows(), the application is responsible for freeing
  1252. row_pointers (and row_pointers[i], if they were separately allocated).
  1253. If you don't allocate row_pointers ahead of time, png_read_png() will
  1254. do it, and it'll be free'ed by libpng when you call png_destroy_*().
  1255. .SS The low-level read interface
  1256. If you are going the low-level route, you are now ready to read all
  1257. the file information up to the actual image data. You do this with a
  1258. call to png_read_info().
  1259. png_read_info(png_ptr, info_ptr);
  1260. This will process all chunks up to but not including the image data.
  1261. This also copies some of the data from the PNG file into the decode structure
  1262. for use in later transformations. Important information copied in is:
  1263. 1) The PNG file gamma from the gAMA chunk. This overwrites the default value
  1264. provided by an earlier call to png_set_gamma or png_set_alpha_mode.
  1265. 2) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
  1266. damages the information provided by an earlier call to png_set_background
  1267. resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
  1268. 3) The number of significant bits in each component value. Libpng uses this to
  1269. optimize gamma handling by reducing the internal lookup table sizes.
  1270. 4) The transparent color information from a tRNS chunk. This can be modified by
  1271. a later call to png_set_tRNS.
  1272. .SS Querying the info structure
  1273. Functions are used to get the information from the info_ptr once it
  1274. has been read. Note that these fields may not be completely filled
  1275. in until png_read_end() has read the chunk data following the image.
  1276. png_get_IHDR(png_ptr, info_ptr, &width, &height,
  1277. &bit_depth, &color_type, &interlace_type,
  1278. &compression_type, &filter_method);
  1279. width - holds the width of the image
  1280. in pixels (up to 2^31).
  1281. height - holds the height of the image
  1282. in pixels (up to 2^31).
  1283. bit_depth - holds the bit depth of one of the
  1284. image channels. (valid values are
  1285. 1, 2, 4, 8, 16 and depend also on
  1286. the color_type. See also
  1287. significant bits (sBIT) below).
  1288. color_type - describes which color/alpha channels
  1289. are present.
  1290. PNG_COLOR_TYPE_GRAY
  1291. (bit depths 1, 2, 4, 8, 16)
  1292. PNG_COLOR_TYPE_GRAY_ALPHA
  1293. (bit depths 8, 16)
  1294. PNG_COLOR_TYPE_PALETTE
  1295. (bit depths 1, 2, 4, 8)
  1296. PNG_COLOR_TYPE_RGB
  1297. (bit_depths 8, 16)
  1298. PNG_COLOR_TYPE_RGB_ALPHA
  1299. (bit_depths 8, 16)
  1300. PNG_COLOR_MASK_PALETTE
  1301. PNG_COLOR_MASK_COLOR
  1302. PNG_COLOR_MASK_ALPHA
  1303. interlace_type - (PNG_INTERLACE_NONE or
  1304. PNG_INTERLACE_ADAM7)
  1305. compression_type - (must be PNG_COMPRESSION_TYPE_BASE
  1306. for PNG 1.0)
  1307. filter_method - (must be PNG_FILTER_TYPE_BASE
  1308. for PNG 1.0, and can also be
  1309. PNG_INTRAPIXEL_DIFFERENCING if
  1310. the PNG datastream is embedded in
  1311. a MNG-1.0 datastream)
  1312. Any or all of interlace_type, compression_type, or
  1313. filter_method can be NULL if you are
  1314. not interested in their values.
  1315. Note that png_get_IHDR() returns 32-bit data into
  1316. the application's width and height variables.
  1317. This is an unsafe situation if these are 16-bit
  1318. variables. In such situations, the
  1319. png_get_image_width() and png_get_image_height()
  1320. functions described below are safer.
  1321. width = png_get_image_width(png_ptr,
  1322. info_ptr);
  1323. height = png_get_image_height(png_ptr,
  1324. info_ptr);
  1325. bit_depth = png_get_bit_depth(png_ptr,
  1326. info_ptr);
  1327. color_type = png_get_color_type(png_ptr,
  1328. info_ptr);
  1329. interlace_type = png_get_interlace_type(png_ptr,
  1330. info_ptr);
  1331. compression_type = png_get_compression_type(png_ptr,
  1332. info_ptr);
  1333. filter_method = png_get_filter_type(png_ptr,
  1334. info_ptr);
  1335. channels = png_get_channels(png_ptr, info_ptr);
  1336. channels - number of channels of info for the
  1337. color type (valid values are 1 (GRAY,
  1338. PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
  1339. 4 (RGB_ALPHA or RGB + filler byte))
  1340. rowbytes = png_get_rowbytes(png_ptr, info_ptr);
  1341. rowbytes - number of bytes needed to hold a row
  1342. signature = png_get_signature(png_ptr, info_ptr);
  1343. signature - holds the signature read from the
  1344. file (if any). The data is kept in
  1345. the same offset it would be if the
  1346. whole signature were read (i.e. if an
  1347. application had already read in 4
  1348. bytes of signature before starting
  1349. libpng, the remaining 4 bytes would
  1350. be in signature[4] through signature[7]
  1351. (see png_set_sig_bytes())).
  1352. These are also important, but their validity depends on whether the chunk
  1353. has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
  1354. png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
  1355. data has been read, or zero if it is missing. The parameters to the
  1356. png_get_<chunk> are set directly if they are simple data types, or a
  1357. pointer into the info_ptr is returned for any complex types.
  1358. png_get_PLTE(png_ptr, info_ptr, &palette,
  1359. &num_palette);
  1360. palette - the palette for the file
  1361. (array of png_color)
  1362. num_palette - number of entries in the palette
  1363. png_get_gAMA(png_ptr, info_ptr, &file_gamma);
  1364. png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
  1365. file_gamma - the gamma at which the file is
  1366. written (PNG_INFO_gAMA)
  1367. int_file_gamma - 100,000 times the gamma at which the
  1368. file is written
  1369. png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x, &red_y,
  1370. &green_x, &green_y, &blue_x, &blue_y)
  1371. png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z, &green_X,
  1372. &green_Y, &green_Z, &blue_X, &blue_Y, &blue_Z)
  1373. png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x, &int_white_y,
  1374. &int_red_x, &int_red_y, &int_green_x, &int_green_y,
  1375. &int_blue_x, &int_blue_y)
  1376. png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
  1377. &int_red_Z, &int_green_X, &int_green_Y, &int_green_Z,
  1378. &int_blue_X, &int_blue_Y, &int_blue_Z)
  1379. {white,red,green,blue}_{x,y}
  1380. A color space encoding specified using the chromaticities
  1381. of the end points and the white point. (PNG_INFO_cHRM)
  1382. {red,green,blue}_{X,Y,Z}
  1383. A color space encoding specified using the encoding end
  1384. points - the CIE tristimulus specification of the intended
  1385. color of the red, green and blue channels in the PNG RGB
  1386. data. The white point is simply the sum of the three end
  1387. points. (PNG_INFO_cHRM)
  1388. png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
  1389. file_srgb_intent - the rendering intent (PNG_INFO_sRGB)
  1390. The presence of the sRGB chunk
  1391. means that the pixel data is in the
  1392. sRGB color space. This chunk also
  1393. implies specific values of gAMA and
  1394. cHRM.
  1395. png_get_iCCP(png_ptr, info_ptr, &name,
  1396. &compression_type, &profile, &proflen);
  1397. name - The profile name.
  1398. compression_type - The compression type; always
  1399. PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
  1400. You may give NULL to this argument to
  1401. ignore it.
  1402. profile - International Color Consortium color
  1403. profile data. May contain NULs.
  1404. proflen - length of profile data in bytes.
  1405. png_get_sBIT(png_ptr, info_ptr, &sig_bit);
  1406. sig_bit - the number of significant bits for
  1407. (PNG_INFO_sBIT) each of the gray,
  1408. red, green, and blue channels,
  1409. whichever are appropriate for the
  1410. given color type (png_color_16)
  1411. png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
  1412. &num_trans, &trans_color);
  1413. trans_alpha - array of alpha (transparency)
  1414. entries for palette (PNG_INFO_tRNS)
  1415. num_trans - number of transparent entries
  1416. (PNG_INFO_tRNS)
  1417. trans_color - graylevel or color sample values of
  1418. the single transparent color for
  1419. non-paletted images (PNG_INFO_tRNS)
  1420. png_get_hIST(png_ptr, info_ptr, &hist);
  1421. (PNG_INFO_hIST)
  1422. hist - histogram of palette (array of
  1423. png_uint_16)
  1424. png_get_tIME(png_ptr, info_ptr, &mod_time);
  1425. mod_time - time image was last modified
  1426. (PNG_VALID_tIME)
  1427. png_get_bKGD(png_ptr, info_ptr, &background);
  1428. background - background color (of type
  1429. png_color_16p) (PNG_VALID_bKGD)
  1430. valid 16-bit red, green and blue
  1431. values, regardless of color_type
  1432. num_comments = png_get_text(png_ptr, info_ptr,
  1433. &text_ptr, &num_text);
  1434. num_comments - number of comments
  1435. text_ptr - array of png_text holding image
  1436. comments
  1437. text_ptr[i].compression - type of compression used
  1438. on "text" PNG_TEXT_COMPRESSION_NONE
  1439. PNG_TEXT_COMPRESSION_zTXt
  1440. PNG_ITXT_COMPRESSION_NONE
  1441. PNG_ITXT_COMPRESSION_zTXt
  1442. text_ptr[i].key - keyword for comment. Must contain
  1443. 1-79 characters.
  1444. text_ptr[i].text - text comments for current
  1445. keyword. Can be empty.
  1446. text_ptr[i].text_length - length of text string,
  1447. after decompression, 0 for iTXt
  1448. text_ptr[i].itxt_length - length of itxt string,
  1449. after decompression, 0 for tEXt/zTXt
  1450. text_ptr[i].lang - language of comment (empty
  1451. string for unknown).
  1452. text_ptr[i].lang_key - keyword in UTF-8
  1453. (empty string for unknown).
  1454. Note that the itxt_length, lang, and lang_key
  1455. members of the text_ptr structure only exist when the
  1456. library is built with iTXt chunk support. Prior to
  1457. libpng-1.4.0 the library was built by default without
  1458. iTXt support. Also note that when iTXt is supported,
  1459. they contain NULL pointers when the "compression"
  1460. field contains PNG_TEXT_COMPRESSION_NONE or
  1461. PNG_TEXT_COMPRESSION_zTXt.
  1462. num_text - number of comments (same as
  1463. num_comments; you can put NULL here
  1464. to avoid the duplication)
  1465. Note while png_set_text() will accept text, language,
  1466. and translated keywords that can be NULL pointers, the
  1467. structure returned by png_get_text will always contain
  1468. regular zero-terminated C strings. They might be
  1469. empty strings but they will never be NULL pointers.
  1470. num_spalettes = png_get_sPLT(png_ptr, info_ptr,
  1471. &palette_ptr);
  1472. num_spalettes - number of sPLT chunks read.
  1473. palette_ptr - array of palette structures holding
  1474. contents of one or more sPLT chunks
  1475. read.
  1476. png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
  1477. &unit_type);
  1478. offset_x - positive offset from the left edge
  1479. of the screen (can be negative)
  1480. offset_y - positive offset from the top edge
  1481. of the screen (can be negative)
  1482. unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
  1483. png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
  1484. &unit_type);
  1485. res_x - pixels/unit physical resolution in
  1486. x direction
  1487. res_y - pixels/unit physical resolution in
  1488. x direction
  1489. unit_type - PNG_RESOLUTION_UNKNOWN,
  1490. PNG_RESOLUTION_METER
  1491. png_get_sCAL(png_ptr, info_ptr, &unit, &width,
  1492. &height)
  1493. unit - physical scale units (an integer)
  1494. width - width of a pixel in physical scale units
  1495. height - height of a pixel in physical scale units
  1496. (width and height are doubles)
  1497. png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
  1498. &height)
  1499. unit - physical scale units (an integer)
  1500. width - width of a pixel in physical scale units
  1501. (expressed as a string)
  1502. height - height of a pixel in physical scale units
  1503. (width and height are strings like "2.54")
  1504. num_unknown_chunks = png_get_unknown_chunks(png_ptr,
  1505. info_ptr, &unknowns)
  1506. unknowns - array of png_unknown_chunk
  1507. structures holding unknown chunks
  1508. unknowns[i].name - name of unknown chunk
  1509. unknowns[i].data - data of unknown chunk
  1510. unknowns[i].size - size of unknown chunk's data
  1511. unknowns[i].location - position of chunk in file
  1512. The value of "i" corresponds to the order in which the
  1513. chunks were read from the PNG file or inserted with the
  1514. png_set_unknown_chunks() function.
  1515. The value of "location" is a bitwise "or" of
  1516. PNG_HAVE_IHDR (0x01)
  1517. PNG_HAVE_PLTE (0x02)
  1518. PNG_AFTER_IDAT (0x08)
  1519. The data from the pHYs chunk can be retrieved in several convenient
  1520. forms:
  1521. res_x = png_get_x_pixels_per_meter(png_ptr,
  1522. info_ptr)
  1523. res_y = png_get_y_pixels_per_meter(png_ptr,
  1524. info_ptr)
  1525. res_x_and_y = png_get_pixels_per_meter(png_ptr,
  1526. info_ptr)
  1527. res_x = png_get_x_pixels_per_inch(png_ptr,
  1528. info_ptr)
  1529. res_y = png_get_y_pixels_per_inch(png_ptr,
  1530. info_ptr)
  1531. res_x_and_y = png_get_pixels_per_inch(png_ptr,
  1532. info_ptr)
  1533. aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
  1534. info_ptr)
  1535. Each of these returns 0 [signifying "unknown"] if
  1536. the data is not present or if res_x is 0;
  1537. res_x_and_y is 0 if res_x != res_y
  1538. Note that because of the way the resolutions are
  1539. stored internally, the inch conversions won't
  1540. come out to exactly even number. For example,
  1541. 72 dpi is stored as 0.28346 pixels/meter, and
  1542. when this is retrieved it is 71.9988 dpi, so
  1543. be sure to round the returned value appropriately
  1544. if you want to display a reasonable-looking result.
  1545. The data from the oFFs chunk can be retrieved in several convenient
  1546. forms:
  1547. x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
  1548. y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
  1549. x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
  1550. y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
  1551. Each of these returns 0 [signifying "unknown" if both
  1552. x and y are 0] if the data is not present or if the
  1553. chunk is present but the unit is the pixel. The
  1554. remark about inexact inch conversions applies here
  1555. as well, because a value in inches can't always be
  1556. converted to microns and back without some loss
  1557. of precision.
  1558. For more information, see the
  1559. PNG specification for chunk contents. Be careful with trusting
  1560. rowbytes, as some of the transformations could increase the space
  1561. needed to hold a row (expand, filler, gray_to_rgb, etc.).
  1562. See png_read_update_info(), below.
  1563. A quick word about text_ptr and num_text. PNG stores comments in
  1564. keyword/text pairs, one pair per chunk, with no limit on the number
  1565. of text chunks, and a 2^31 byte limit on their size. While there are
  1566. suggested keywords, there is no requirement to restrict the use to these
  1567. strings. It is strongly suggested that keywords and text be sensible
  1568. to humans (that's the point), so don't use abbreviations. Non-printing
  1569. symbols are not allowed. See the PNG specification for more details.
  1570. There is also no requirement to have text after the keyword.
  1571. Keywords should be limited to 79 Latin-1 characters without leading or
  1572. trailing spaces, but non-consecutive spaces are allowed within the
  1573. keyword. It is possible to have the same keyword any number of times.
  1574. The text_ptr is an array of png_text structures, each holding a
  1575. pointer to a language string, a pointer to a keyword and a pointer to
  1576. a text string. The text string, language code, and translated
  1577. keyword may be empty or NULL pointers. The keyword/text
  1578. pairs are put into the array in the order that they are received.
  1579. However, some or all of the text chunks may be after the image, so, to
  1580. make sure you have read all the text chunks, don't mess with these
  1581. until after you read the stuff after the image. This will be
  1582. mentioned again below in the discussion that goes with png_read_end().
  1583. .SS Input transformations
  1584. After you've read the header information, you can set up the library
  1585. to handle any special transformations of the image data. The various
  1586. ways to transform the data will be described in the order that they
  1587. should occur. This is important, as some of these change the color
  1588. type and/or bit depth of the data, and some others only work on
  1589. certain color types and bit depths.
  1590. Transformations you request are ignored if they don't have any meaning for a
  1591. particular input data format. However some transformations can have an effect
  1592. as a result of a previous transformation. If you specify a contradictory set of
  1593. transformations, for example both adding and removing the alpha channel, you
  1594. cannot predict the final result.
  1595. The color used for the transparency values should be supplied in the same
  1596. format/depth as the current image data. It is stored in the same format/depth
  1597. as the image data in a tRNS chunk, so this is what libpng expects for this data.
  1598. The color used for the background value depends on the need_expand argument as
  1599. described below.
  1600. Data will be decoded into the supplied row buffers packed into bytes
  1601. unless the library has been told to transform it into another format.
  1602. For example, 4 bit/pixel paletted or grayscale data will be returned
  1603. 2 pixels/byte with the leftmost pixel in the high-order bits of the
  1604. byte, unless png_set_packing() is called. 8-bit RGB data will be stored
  1605. in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
  1606. is called to insert filler bytes, either before or after each RGB triplet.
  1607. 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
  1608. byte of the color value first, unless png_set_scale_16() is called to
  1609. transform it to regular RGB RGB triplets, or png_set_filler() or
  1610. png_set_add alpha() is called to insert filler bytes, either before or
  1611. after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
  1612. be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
  1613. or png_set_scale_16().
  1614. The following code transforms grayscale images of less than 8 to 8 bits,
  1615. changes paletted images to RGB, and adds a full alpha channel if there is
  1616. transparency information in a tRNS chunk. This is most useful on
  1617. grayscale images with bit depths of 2 or 4 or if there is a multiple-image
  1618. viewing application that wishes to treat all images in the same way.
  1619. if (color_type == PNG_COLOR_TYPE_PALETTE)
  1620. png_set_palette_to_rgb(png_ptr);
  1621. if (png_get_valid(png_ptr, info_ptr,
  1622. PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
  1623. if (color_type == PNG_COLOR_TYPE_GRAY &&
  1624. bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
  1625. The first two functions are actually aliases for png_set_expand(), added
  1626. in libpng version 1.0.4, with the function names expanded to improve code
  1627. readability. In some future version they may actually do different
  1628. things.
  1629. As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
  1630. added. It expands the sample depth without changing tRNS to alpha.
  1631. As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
  1632. png_set_expand(); however, the resultant channels have 16 bits rather than 8.
  1633. Use this when the output color or gray channels are made linear to avoid fairly
  1634. severe accuracy loss.
  1635. if (bit_depth < 16)
  1636. png_set_expand_16(png_ptr);
  1637. PNG can have files with 16 bits per channel. If you only can handle
  1638. 8 bits per channel, this will strip the pixels down to 8-bit.
  1639. if (bit_depth == 16)
  1640. #if PNG_LIBPNG_VER >= 10504
  1641. png_set_scale_16(png_ptr);
  1642. #else
  1643. png_set_strip_16(png_ptr);
  1644. #endif
  1645. (The more accurate "png_set_scale_16()" API became available in libpng version
  1646. 1.5.4).
  1647. If you need to process the alpha channel on the image separately from the image
  1648. data (for example if you convert it to a bitmap mask) it is possible to have
  1649. libpng strip the channel leaving just RGB or gray data:
  1650. if (color_type & PNG_COLOR_MASK_ALPHA)
  1651. png_set_strip_alpha(png_ptr);
  1652. If you strip the alpha channel you need to find some other way of dealing with
  1653. the information. If, instead, you want to convert the image to an opaque
  1654. version with no alpha channel use png_set_background; see below.
  1655. As of libpng version 1.5.2, almost all useful expansions are supported, the
  1656. major ommissions are conversion of grayscale to indexed images (which can be
  1657. done trivially in the application) and conversion of indexed to grayscale (which
  1658. can be done by a trivial manipulation of the palette.)
  1659. In the following table, the 01 means grayscale with depth<8, 31 means
  1660. indexed with depth<8, other numerals represent the color type, "T" means
  1661. the tRNS chunk is present, A means an alpha channel is present, and O
  1662. means tRNS or alpha is present but all pixels in the image are opaque.
  1663. FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
  1664. TO
  1665. 01 - [G] - - - - - - - - - - - - -
  1666. 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
  1667. 0 1 G + . . G G G G G G B B GB GB
  1668. 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
  1669. 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
  1670. 2 C P C C C + . . C - - CB CB B B
  1671. 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
  1672. 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
  1673. 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
  1674. 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
  1675. 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
  1676. 4A lA G A T T GA GT GT GA GT GT + BA G GBA
  1677. 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
  1678. 6A CA PA CA C C A T tT PA P P C CBA + BA
  1679. 6O CA PBA CA C C A tT T PA P P CBA C BA +
  1680. Within the matrix,
  1681. "+" identifies entries where 'from' and 'to' are the same.
  1682. "-" means the transformation is not supported.
  1683. "." means nothing is necessary (a tRNS chunk can just be ignored).
  1684. "t" means the transformation is obtained by png_set_tRNS.
  1685. "A" means the transformation is obtained by png_set_add_alpha().
  1686. "X" means the transformation is obtained by png_set_expand().
  1687. "1" means the transformation is obtained by
  1688. png_set_expand_gray_1_2_4_to_8() (and by png_set_expand() if there
  1689. is no transparency in the original or the final format).
  1690. "C" means the transformation is obtained by png_set_gray_to_rgb().
  1691. "G" means the transformation is obtained by png_set_rgb_to_gray().
  1692. "P" means the transformation is obtained by
  1693. png_set_expand_palette_to_rgb().
  1694. "p" means the transformation is obtained by png_set_packing().
  1695. "Q" means the transformation is obtained by png_set_quantize().
  1696. "T" means the transformation is obtained by png_set_tRNS_to_alpha().
  1697. "B" means the transformation is obtained by png_set_background(), or
  1698. png_strip_alpha().
  1699. When an entry has multiple transforms listed all are required to cause the
  1700. right overall transformation. When two transforms are separated by a comma
  1701. either will do the job. When transforms are enclosed in [] the transform should
  1702. do the job but this is currently unimplemented - a different format will result
  1703. if the suggested transformations are used.
  1704. In PNG files, the alpha channel in an image
  1705. is the level of opacity. If you need the alpha channel in an image to
  1706. be the level of transparency instead of opacity, you can invert the
  1707. alpha channel (or the tRNS chunk data) after it's read, so that 0 is
  1708. fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
  1709. images) is fully transparent, with
  1710. png_set_invert_alpha(png_ptr);
  1711. PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
  1712. they can, resulting in, for example, 8 pixels per byte for 1 bit
  1713. files. This code expands to 1 pixel per byte without changing the
  1714. values of the pixels:
  1715. if (bit_depth < 8)
  1716. png_set_packing(png_ptr);
  1717. PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
  1718. stored in a PNG image have been "scaled" or "shifted" up to the next
  1719. higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
  1720. to 8 bits/sample in the range [0, 255]). However, it is also possible
  1721. to convert the PNG pixel data back to the original bit depth of the
  1722. image. This call reduces the pixels back down to the original bit depth:
  1723. png_color_8p sig_bit;
  1724. if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
  1725. png_set_shift(png_ptr, sig_bit);
  1726. PNG files store 3-color pixels in red, green, blue order. This code
  1727. changes the storage of the pixels to blue, green, red:
  1728. if (color_type == PNG_COLOR_TYPE_RGB ||
  1729. color_type == PNG_COLOR_TYPE_RGB_ALPHA)
  1730. png_set_bgr(png_ptr);
  1731. PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
  1732. into 4 or 8 bytes for windowing systems that need them in this format:
  1733. if (color_type == PNG_COLOR_TYPE_RGB)
  1734. png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
  1735. where "filler" is the 8 or 16-bit number to fill with, and the location is
  1736. either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
  1737. you want the filler before the RGB or after. This transformation
  1738. does not affect images that already have full alpha channels. To add an
  1739. opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
  1740. will generate RGBA pixels.
  1741. Note that png_set_filler() does not change the color type. If you want
  1742. to do that, you can add a true alpha channel with
  1743. if (color_type == PNG_COLOR_TYPE_RGB ||
  1744. color_type == PNG_COLOR_TYPE_GRAY)
  1745. png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
  1746. where "filler" contains the alpha value to assign to each pixel.
  1747. This function was added in libpng-1.2.7.
  1748. If you are reading an image with an alpha channel, and you need the
  1749. data as ARGB instead of the normal PNG format RGBA:
  1750. if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
  1751. png_set_swap_alpha(png_ptr);
  1752. For some uses, you may want a grayscale image to be represented as
  1753. RGB. This code will do that conversion:
  1754. if (color_type == PNG_COLOR_TYPE_GRAY ||
  1755. color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
  1756. png_set_gray_to_rgb(png_ptr);
  1757. Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
  1758. with alpha.
  1759. if (color_type == PNG_COLOR_TYPE_RGB ||
  1760. color_type == PNG_COLOR_TYPE_RGB_ALPHA)
  1761. png_set_rgb_to_gray(png_ptr, error_action, double red_weight,
  1762. double green_weight);
  1763. error_action = 1: silently do the conversion
  1764. error_action = 2: issue a warning if the original
  1765. image has any pixel where
  1766. red != green or red != blue
  1767. error_action = 3: issue an error and abort the
  1768. conversion if the original
  1769. image has any pixel where
  1770. red != green or red != blue
  1771. red_weight: weight of red component
  1772. green_weight: weight of green component
  1773. If either weight is negative, default
  1774. weights are used.
  1775. In the corresponding fixed point API the red_weight and green_weight values are
  1776. simply scaled by 100,000:
  1777. png_set_rgb_to_gray(png_ptr, error_action, png_fixed_point red_weight,
  1778. png_fixed_point green_weight);
  1779. If you have set error_action = 1 or 2, you can
  1780. later check whether the image really was gray, after processing
  1781. the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
  1782. It will return a png_byte that is zero if the image was gray or
  1783. 1 if there were any non-gray pixels. Background and sBIT data
  1784. will be silently converted to grayscale, using the green channel
  1785. data for sBIT, regardless of the error_action setting.
  1786. The default values come from the PNG file cHRM chunk if present; otherwise, the
  1787. defaults correspond to the ITU-R recommendation 709, and also the sRGB color
  1788. space, as recommended in the Charles Poynton's Colour FAQ,
  1789. <http://www.poynton.com/>, in section 9:
  1790. <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
  1791. Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
  1792. Previous versions of this document, 1998 through 2002, recommended a slightly
  1793. different formula:
  1794. Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
  1795. Libpng uses an integer approximation:
  1796. Y = (6968 * R + 23434 * G + 2366 * B)/32768
  1797. The calculation is done in a linear colorspace, if the image gamma
  1798. can be determined.
  1799. The png_set_background() function has been described already; it tells libpng to
  1800. composite images with alpha or simple transparency against the supplied
  1801. background color. For compatibility with versions of libpng earlier than
  1802. libpng-1.5.4 it is recommended that you call the function after reading the file
  1803. header, even if you don't want to use the color in a bKGD chunk, if one exists.
  1804. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
  1805. you may use this color, or supply another color more suitable for
  1806. the current display (e.g., the background color from a web page). You
  1807. need to tell libpng how the color is represented, both the format of the
  1808. component values in the color (the number of bits) and the gamma encoding of the
  1809. color. The function takes two arguments, background_gamma_mode and need_expand
  1810. to convey this information, however only two combinations are likely to be
  1811. useful:
  1812. png_color_16 my_background;
  1813. png_color_16p image_background;
  1814. if (png_get_bKGD(png_ptr, info_ptr, &image_background))
  1815. png_set_background(png_ptr, image_background,
  1816. PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
  1817. else
  1818. png_set_background(png_ptr, &my_background,
  1819. PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
  1820. The second call was described above - my_background is in the format of the
  1821. final, display, output produced by libpng. Because you now know the format of
  1822. the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
  1823. output and to retain palette images (the palette colors will be modified
  1824. appropriately and the tRNS chunk removed.) However, if you are doing this,
  1825. take great care not to ask for transformations without checking first that
  1826. they apply!
  1827. In the first call the background color has the original bit depth and color type
  1828. of the PNG file. So, for palette images the color is supplied as a palette
  1829. index and for low bit greyscale images the color is a reduced bit value in
  1830. image_background->gray.
  1831. If you didn't call png_set_gamma() before reading the file header, for example
  1832. if you need your code to remain compatible with older versions of libpng prior
  1833. to libpng-1.5.4, this is the place to call it.
  1834. Do not call it if you called png_set_alpha_mode(); doing so will damage the
  1835. settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
  1836. supported then you can certainly do png_set_gamma() before reading the PNG
  1837. header.)
  1838. This API unconditionally sets the screen and file gamma values, so it will
  1839. override the value in the PNG file unless it is called before the PNG file
  1840. reading starts. For this reason you must always call it with the PNG file
  1841. value when you call it in this position:
  1842. if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
  1843. png_set_gamma(png_ptr, screen_gamma, file_gamma);
  1844. else
  1845. png_set_gamma(png_ptr, screen_gamma, 0.45455);
  1846. If you need to reduce an RGB file to a paletted file, or if a paletted
  1847. file has more entries then will fit on your screen, png_set_quantize()
  1848. will do that. Note that this is a simple match quantization that merely
  1849. finds the closest color available. This should work fairly well with
  1850. optimized palettes, but fairly badly with linear color cubes. If you
  1851. pass a palette that is larger than maximum_colors, the file will
  1852. reduce the number of colors in the palette so it will fit into
  1853. maximum_colors. If there is a histogram, libpng will use it to make
  1854. more intelligent choices when reducing the palette. If there is no
  1855. histogram, it may not do as good a job.
  1856. if (color_type & PNG_COLOR_MASK_COLOR)
  1857. {
  1858. if (png_get_valid(png_ptr, info_ptr,
  1859. PNG_INFO_PLTE))
  1860. {
  1861. png_uint_16p histogram = NULL;
  1862. png_get_hIST(png_ptr, info_ptr,
  1863. &histogram);
  1864. png_set_quantize(png_ptr, palette, num_palette,
  1865. max_screen_colors, histogram, 1);
  1866. }
  1867. else
  1868. {
  1869. png_color std_color_cube[MAX_SCREEN_COLORS] =
  1870. { ... colors ... };
  1871. png_set_quantize(png_ptr, std_color_cube,
  1872. MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
  1873. NULL,0);
  1874. }
  1875. }
  1876. PNG files describe monochrome as black being zero and white being one.
  1877. The following code will reverse this (make black be one and white be
  1878. zero):
  1879. if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
  1880. png_set_invert_mono(png_ptr);
  1881. This function can also be used to invert grayscale and gray-alpha images:
  1882. if (color_type == PNG_COLOR_TYPE_GRAY ||
  1883. color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
  1884. png_set_invert_mono(png_ptr);
  1885. PNG files store 16-bit pixels in network byte order (big-endian,
  1886. ie. most significant bits first). This code changes the storage to the
  1887. other way (little-endian, i.e. least significant bits first, the
  1888. way PCs store them):
  1889. if (bit_depth == 16)
  1890. png_set_swap(png_ptr);
  1891. If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
  1892. need to change the order the pixels are packed into bytes, you can use:
  1893. if (bit_depth < 8)
  1894. png_set_packswap(png_ptr);
  1895. Finally, you can write your own transformation function if none of
  1896. the existing ones meets your needs. This is done by setting a callback
  1897. with
  1898. png_set_read_user_transform_fn(png_ptr,
  1899. read_transform_fn);
  1900. You must supply the function
  1901. void read_transform_fn(png_structp png_ptr, png_row_infop
  1902. row_info, png_bytep data)
  1903. See pngtest.c for a working example. Your function will be called
  1904. after all of the other transformations have been processed. Take care with
  1905. interlaced images if you do the interlace yourself - the width of the row is the
  1906. width in 'row_info', not the overall image width.
  1907. If supported, libpng provides two information routines that you can use to find
  1908. where you are in processing the image:
  1909. png_get_current_pass_number(png_structp png_ptr);
  1910. png_get_current_row_number(png_structp png_ptr);
  1911. Don't try using these outside a transform callback - firstly they are only
  1912. supported if user transforms are supported, secondly they may well return
  1913. unexpected results unless the row is actually being processed at the moment they
  1914. are called.
  1915. With interlaced
  1916. images the value returned is the row in the input sub-image image. Use
  1917. PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
  1918. find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
  1919. The discussion of interlace handling above contains more information on how to
  1920. use these values.
  1921. You can also set up a pointer to a user structure for use by your
  1922. callback function, and you can inform libpng that your transform
  1923. function will change the number of channels or bit depth with the
  1924. function
  1925. png_set_user_transform_info(png_ptr, user_ptr,
  1926. user_depth, user_channels);
  1927. The user's application, not libpng, is responsible for allocating and
  1928. freeing any memory required for the user structure.
  1929. You can retrieve the pointer via the function
  1930. png_get_user_transform_ptr(). For example:
  1931. voidp read_user_transform_ptr =
  1932. png_get_user_transform_ptr(png_ptr);
  1933. The last thing to handle is interlacing; this is covered in detail below,
  1934. but you must call the function here if you want libpng to handle expansion
  1935. of the interlaced image.
  1936. number_of_passes = png_set_interlace_handling(png_ptr);
  1937. After setting the transformations, libpng can update your png_info
  1938. structure to reflect any transformations you've requested with this
  1939. call.
  1940. png_read_update_info(png_ptr, info_ptr);
  1941. This is most useful to update the info structure's rowbytes
  1942. field so you can use it to allocate your image memory. This function
  1943. will also update your palette with the correct screen_gamma and
  1944. background if these have been given with the calls above. You may
  1945. only call png_read_update_info() once with a particular info_ptr.
  1946. After you call png_read_update_info(), you can allocate any
  1947. memory you need to hold the image. The row data is simply
  1948. raw byte data for all forms of images. As the actual allocation
  1949. varies among applications, no example will be given. If you
  1950. are allocating one large chunk, you will need to build an
  1951. array of pointers to each row, as it will be needed for some
  1952. of the functions below.
  1953. Remember: Before you call png_read_update_info(), the png_get_*()
  1954. functions return the values corresponding to the original PNG image.
  1955. After you call png_read_update_info the values refer to the image
  1956. that libpng will output. Consequently you must call all the png_set_
  1957. functions before you call png_read_update_info(). This is particularly
  1958. important for png_set_interlace_handling() - if you are going to call
  1959. png_read_update_info() you must call png_set_interlace_handling() before
  1960. it unless you want to receive interlaced output.
  1961. .SS Reading image data
  1962. After you've allocated memory, you can read the image data.
  1963. The simplest way to do this is in one function call. If you are
  1964. allocating enough memory to hold the whole image, you can just
  1965. call png_read_image() and libpng will read in all the image data
  1966. and put it in the memory area supplied. You will need to pass in
  1967. an array of pointers to each row.
  1968. This function automatically handles interlacing, so you don't
  1969. need to call png_set_interlace_handling() (unless you call
  1970. png_read_update_info()) or call this function multiple times, or any
  1971. of that other stuff necessary with png_read_rows().
  1972. png_read_image(png_ptr, row_pointers);
  1973. where row_pointers is:
  1974. png_bytep row_pointers[height];
  1975. You can point to void or char or whatever you use for pixels.
  1976. If you don't want to read in the whole image at once, you can
  1977. use png_read_rows() instead. If there is no interlacing (check
  1978. interlace_type == PNG_INTERLACE_NONE), this is simple:
  1979. png_read_rows(png_ptr, row_pointers, NULL,
  1980. number_of_rows);
  1981. where row_pointers is the same as in the png_read_image() call.
  1982. If you are doing this just one row at a time, you can do this with
  1983. a single row_pointer instead of an array of row_pointers:
  1984. png_bytep row_pointer = row;
  1985. png_read_row(png_ptr, row_pointer, NULL);
  1986. If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
  1987. get somewhat harder. The only current (PNG Specification version 1.2)
  1988. interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
  1989. a somewhat complicated 2D interlace scheme, known as Adam7, that
  1990. breaks down an image into seven smaller images of varying size, based
  1991. on an 8x8 grid. This number is defined (from libpng 1.5) as
  1992. PNG_INTERLACE_ADAM7_PASSES in png.h
  1993. libpng can fill out those images or it can give them to you "as is".
  1994. It is almost always better to have libpng handle the interlacing for you.
  1995. If you want the images filled out, there are two ways to do that. The one
  1996. mentioned in the PNG specification is to expand each pixel to cover
  1997. those pixels that have not been read yet (the "rectangle" method).
  1998. This results in a blocky image for the first pass, which gradually
  1999. smooths out as more pixels are read. The other method is the "sparkle"
  2000. method, where pixels are drawn only in their final locations, with the
  2001. rest of the image remaining whatever colors they were initialized to
  2002. before the start of the read. The first method usually looks better,
  2003. but tends to be slower, as there are more pixels to put in the rows.
  2004. If, as is likely, you want libpng to expand the images, call this before
  2005. calling png_start_read_image() or png_read_update_info():
  2006. if (interlace_type == PNG_INTERLACE_ADAM7)
  2007. number_of_passes
  2008. = png_set_interlace_handling(png_ptr);
  2009. This will return the number of passes needed. Currently, this is seven,
  2010. but may change if another interlace type is added. This function can be
  2011. called even if the file is not interlaced, where it will return one pass.
  2012. You then need to read the whole image 'number_of_passes' times. Each time
  2013. will distribute the pixels from the current pass to the correct place in
  2014. the output image, so you need to supply the same rows to png_read_rows in
  2015. each pass.
  2016. If you are not going to display the image after each pass, but are
  2017. going to wait until the entire image is read in, use the sparkle
  2018. effect. This effect is faster and the end result of either method
  2019. is exactly the same. If you are planning on displaying the image
  2020. after each pass, the "rectangle" effect is generally considered the
  2021. better looking one.
  2022. If you only want the "sparkle" effect, just call png_read_rows() as
  2023. normal, with the third parameter NULL. Make sure you make pass over
  2024. the image number_of_passes times, and you don't change the data in the
  2025. rows between calls. You can change the locations of the data, just
  2026. not the data. Each pass only writes the pixels appropriate for that
  2027. pass, and assumes the data from previous passes is still valid.
  2028. png_read_rows(png_ptr, row_pointers, NULL,
  2029. number_of_rows);
  2030. If you only want the first effect (the rectangles), do the same as
  2031. before except pass the row buffer in the third parameter, and leave
  2032. the second parameter NULL.
  2033. png_read_rows(png_ptr, NULL, row_pointers,
  2034. number_of_rows);
  2035. If you don't want libpng to handle the interlacing details, just call
  2036. png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
  2037. Each of the images is a valid image by itself, however you will almost
  2038. certainly need to distribute the pixels from each sub-image to the
  2039. correct place. This is where everything gets very tricky.
  2040. If you want to retrieve the separate images you must pass the correct
  2041. number of rows to each successive call of png_read_rows(). The calculation
  2042. gets pretty complicated for small images, where some sub-images may
  2043. not even exist because either their width or height ends up zero.
  2044. libpng provides two macros to help you in 1.5 and later versions:
  2045. png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
  2046. png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
  2047. Respectively these tell you the width and height of the sub-image
  2048. corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
  2049. this can be confusing because the specification refers to the same passes
  2050. as 1 to 7! Be careful, you must check both the width and height before
  2051. calling png_read_rows() and not call it for that pass if either is zero.
  2052. You can, of course, read each sub-image row by row. If you want to
  2053. produce optimal code to make a pixel-by-pixel transformation of an
  2054. interlaced image this is the best approach; read each row of each pass,
  2055. transform it, and write it out to a new interlaced image.
  2056. If you want to de-interlace the image yourself libpng provides further
  2057. macros to help that tell you where to place the pixels in the output image.
  2058. Because the interlacing scheme is rectangular - sub-image pixels are always
  2059. arranged on a rectangular grid - all you need to know for each pass is the
  2060. starting column and row in the output image of the first pixel plus the
  2061. spacing between each pixel. As of libpng 1.5 there are four macros to
  2062. retrieve this information:
  2063. png_uint_32 x = PNG_PASS_START_COL(pass);
  2064. png_uint_32 y = PNG_PASS_START_ROW(pass);
  2065. png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
  2066. png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
  2067. These allow you to write the obvious loop:
  2068. png_uint_32 input_y = 0;
  2069. png_uint_32 output_y = PNG_PASS_START_ROW(pass);
  2070. while (output_y < output_image_height)
  2071. {
  2072. png_uint_32 input_x = 0;
  2073. png_uint_32 output_x = PNG_PASS_START_COL(pass);
  2074. while (output_x < output_image_width)
  2075. {
  2076. image[output_y][output_x] =
  2077. subimage[pass][input_y][input_x++];
  2078. output_x += xStep;
  2079. }
  2080. ++input_y;
  2081. output_y += yStep;
  2082. }
  2083. Notice that the steps between successive output rows and columns are
  2084. returned as shifts. This is possible because the pixels in the subimages
  2085. are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
  2086. image. In practice you may need to directly calculate the output coordinate
  2087. given an input coordinate. libpng provides two further macros for this
  2088. purpose:
  2089. png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
  2090. png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
  2091. Finally a pair of macros are provided to tell you if a particular image
  2092. row or column appears in a given pass:
  2093. int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
  2094. int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
  2095. Bear in mind that you will probably also need to check the width and height
  2096. of the pass in addition to the above to be sure the pass even exists!
  2097. With any luck you are convinced by now that you don't want to do your own
  2098. interlace handling. In reality normally the only good reason for doing this
  2099. is if you are processing PNG files on a pixel-by-pixel basis and don't want
  2100. to load the whole file into memory when it is interlaced.
  2101. libpng includes a test program, pngvalid, that illustrates reading and
  2102. writing of interlaced images. If you can't get interlacing to work in your
  2103. code and don't want to leave it to libpng (the recommended approach), see
  2104. how pngvalid.c does it.
  2105. .SS Finishing a sequential read
  2106. After you are finished reading the image through the
  2107. low-level interface, you can finish reading the file. If you are
  2108. interested in comments or time, which may be stored either before or
  2109. after the image data, you should pass the separate png_info struct if
  2110. you want to keep the comments from before and after the image
  2111. separate.
  2112. png_infop end_info = png_create_info_struct(png_ptr);
  2113. if (!end_info)
  2114. {
  2115. png_destroy_read_struct(&png_ptr, &info_ptr,
  2116. (png_infopp)NULL);
  2117. return (ERROR);
  2118. }
  2119. png_read_end(png_ptr, end_info);
  2120. If you are not interested, you should still call png_read_end()
  2121. but you can pass NULL, avoiding the need to create an end_info structure.
  2122. png_read_end(png_ptr, (png_infop)NULL);
  2123. If you don't call png_read_end(), then your file pointer will be
  2124. left pointing to the first chunk after the last IDAT, which is probably
  2125. not what you want if you expect to read something beyond the end of
  2126. the PNG datastream.
  2127. When you are done, you can free all memory allocated by libpng like this:
  2128. png_destroy_read_struct(&png_ptr, &info_ptr,
  2129. &end_info);
  2130. or, if you didn't create an end_info structure,
  2131. png_destroy_read_struct(&png_ptr, &info_ptr,
  2132. (png_infopp)NULL);
  2133. It is also possible to individually free the info_ptr members that
  2134. point to libpng-allocated storage with the following function:
  2135. png_free_data(png_ptr, info_ptr, mask, seq)
  2136. mask - identifies data to be freed, a mask
  2137. containing the bitwise OR of one or
  2138. more of
  2139. PNG_FREE_PLTE, PNG_FREE_TRNS,
  2140. PNG_FREE_HIST, PNG_FREE_ICCP,
  2141. PNG_FREE_PCAL, PNG_FREE_ROWS,
  2142. PNG_FREE_SCAL, PNG_FREE_SPLT,
  2143. PNG_FREE_TEXT, PNG_FREE_UNKN,
  2144. or simply PNG_FREE_ALL
  2145. seq - sequence number of item to be freed
  2146. (-1 for all items)
  2147. This function may be safely called when the relevant storage has
  2148. already been freed, or has not yet been allocated, or was allocated
  2149. by the user and not by libpng, and will in those cases do nothing.
  2150. The "seq" parameter is ignored if only one item of the selected data
  2151. type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
  2152. are allowed for the data type identified in the mask, such as text or
  2153. sPLT, only the n'th item in the structure is freed, where n is "seq".
  2154. The default behavior is only to free data that was allocated internally
  2155. by libpng. This can be changed, so that libpng will not free the data,
  2156. or so that it will free data that was allocated by the user with png_malloc()
  2157. or png_zalloc() and passed in via a png_set_*() function, with
  2158. png_data_freer(png_ptr, info_ptr, freer, mask)
  2159. freer - one of
  2160. PNG_DESTROY_WILL_FREE_DATA
  2161. PNG_SET_WILL_FREE_DATA
  2162. PNG_USER_WILL_FREE_DATA
  2163. mask - which data elements are affected
  2164. same choices as in png_free_data()
  2165. This function only affects data that has already been allocated.
  2166. You can call this function after reading the PNG data but before calling
  2167. any png_set_*() functions, to control whether the user or the png_set_*()
  2168. function is responsible for freeing any existing data that might be present,
  2169. and again after the png_set_*() functions to control whether the user
  2170. or png_destroy_*() is supposed to free the data. When the user assumes
  2171. responsibility for libpng-allocated data, the application must use
  2172. png_free() to free it, and when the user transfers responsibility to libpng
  2173. for data that the user has allocated, the user must have used png_malloc()
  2174. or png_zalloc() to allocate it.
  2175. If you allocated your row_pointers in a single block, as suggested above in
  2176. the description of the high level read interface, you must not transfer
  2177. responsibility for freeing it to the png_set_rows or png_read_destroy function,
  2178. because they would also try to free the individual row_pointers[i].
  2179. If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
  2180. separately, do not transfer responsibility for freeing text_ptr to libpng,
  2181. because when libpng fills a png_text structure it combines these members with
  2182. the key member, and png_free_data() will free only text_ptr.key. Similarly,
  2183. if you transfer responsibility for free'ing text_ptr from libpng to your
  2184. application, your application must not separately free those members.
  2185. The png_free_data() function will turn off the "valid" flag for anything
  2186. it frees. If you need to turn the flag off for a chunk that was freed by
  2187. your application instead of by libpng, you can use
  2188. png_set_invalid(png_ptr, info_ptr, mask);
  2189. mask - identifies the chunks to be made invalid,
  2190. containing the bitwise OR of one or
  2191. more of
  2192. PNG_INFO_gAMA, PNG_INFO_sBIT,
  2193. PNG_INFO_cHRM, PNG_INFO_PLTE,
  2194. PNG_INFO_tRNS, PNG_INFO_bKGD,
  2195. PNG_INFO_hIST, PNG_INFO_pHYs,
  2196. PNG_INFO_oFFs, PNG_INFO_tIME,
  2197. PNG_INFO_pCAL, PNG_INFO_sRGB,
  2198. PNG_INFO_iCCP, PNG_INFO_sPLT,
  2199. PNG_INFO_sCAL, PNG_INFO_IDAT
  2200. For a more compact example of reading a PNG image, see the file example.c.
  2201. .SS Reading PNG files progressively
  2202. The progressive reader is slightly different then the non-progressive
  2203. reader. Instead of calling png_read_info(), png_read_rows(), and
  2204. png_read_end(), you make one call to png_process_data(), which calls
  2205. callbacks when it has the info, a row, or the end of the image. You
  2206. set up these callbacks with png_set_progressive_read_fn(). You don't
  2207. have to worry about the input/output functions of libpng, as you are
  2208. giving the library the data directly in png_process_data(). I will
  2209. assume that you have read the section on reading PNG files above,
  2210. so I will only highlight the differences (although I will show
  2211. all of the code).
  2212. png_structp png_ptr;
  2213. png_infop info_ptr;
  2214. /* An example code fragment of how you would
  2215. initialize the progressive reader in your
  2216. application. */
  2217. int
  2218. initialize_png_reader()
  2219. {
  2220. png_ptr = png_create_read_struct
  2221. (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
  2222. user_error_fn, user_warning_fn);
  2223. if (!png_ptr)
  2224. return (ERROR);
  2225. info_ptr = png_create_info_struct(png_ptr);
  2226. if (!info_ptr)
  2227. {
  2228. png_destroy_read_struct(&png_ptr,
  2229. (png_infopp)NULL, (png_infopp)NULL);
  2230. return (ERROR);
  2231. }
  2232. if (setjmp(png_jmpbuf(png_ptr)))
  2233. {
  2234. png_destroy_read_struct(&png_ptr, &info_ptr,
  2235. (png_infopp)NULL);
  2236. return (ERROR);
  2237. }
  2238. /* This one's new. You can provide functions
  2239. to be called when the header info is valid,
  2240. when each row is completed, and when the image
  2241. is finished. If you aren't using all functions,
  2242. you can specify NULL parameters. Even when all
  2243. three functions are NULL, you need to call
  2244. png_set_progressive_read_fn(). You can use
  2245. any struct as the user_ptr (cast to a void pointer
  2246. for the function call), and retrieve the pointer
  2247. from inside the callbacks using the function
  2248. png_get_progressive_ptr(png_ptr);
  2249. which will return a void pointer, which you have
  2250. to cast appropriately.
  2251. */
  2252. png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
  2253. info_callback, row_callback, end_callback);
  2254. return 0;
  2255. }
  2256. /* A code fragment that you call as you receive blocks
  2257. of data */
  2258. int
  2259. process_data(png_bytep buffer, png_uint_32 length)
  2260. {
  2261. if (setjmp(png_jmpbuf(png_ptr)))
  2262. {
  2263. png_destroy_read_struct(&png_ptr, &info_ptr,
  2264. (png_infopp)NULL);
  2265. return (ERROR);
  2266. }
  2267. /* This one's new also. Simply give it a chunk
  2268. of data from the file stream (in order, of
  2269. course). On machines with segmented memory
  2270. models machines, don't give it any more than
  2271. 64K. The library seems to run fine with sizes
  2272. of 4K. Although you can give it much less if
  2273. necessary (I assume you can give it chunks of
  2274. 1 byte, I haven't tried less then 256 bytes
  2275. yet). When this function returns, you may
  2276. want to display any rows that were generated
  2277. in the row callback if you don't already do
  2278. so there.
  2279. */
  2280. png_process_data(png_ptr, info_ptr, buffer, length);
  2281. /* At this point you can call png_process_data_skip if
  2282. you want to handle data the library will skip yourself;
  2283. it simply returns the number of bytes to skip (and stops
  2284. libpng skipping that number of bytes on the next
  2285. png_process_data call).
  2286. return 0;
  2287. }
  2288. /* This function is called (as set by
  2289. png_set_progressive_read_fn() above) when enough data
  2290. has been supplied so all of the header has been
  2291. read.
  2292. */
  2293. void
  2294. info_callback(png_structp png_ptr, png_infop info)
  2295. {
  2296. /* Do any setup here, including setting any of
  2297. the transformations mentioned in the Reading
  2298. PNG files section. For now, you _must_ call
  2299. either png_start_read_image() or
  2300. png_read_update_info() after all the
  2301. transformations are set (even if you don't set
  2302. any). You may start getting rows before
  2303. png_process_data() returns, so this is your
  2304. last chance to prepare for that.
  2305. This is where you turn on interlace handling,
  2306. assuming you don't want to do it yourself.
  2307. If you need to you can stop the processing of
  2308. your original input data at this point by calling
  2309. png_process_data_pause. This returns the number
  2310. of unprocessed bytes from the last png_process_data
  2311. call - it is up to you to ensure that the next call
  2312. sees these bytes again. If you don't want to bother
  2313. with this you can get libpng to cache the unread
  2314. bytes by setting the 'save' parameter (see png.h) but
  2315. then libpng will have to copy the data internally.
  2316. */
  2317. }
  2318. /* This function is called when each row of image
  2319. data is complete */
  2320. void
  2321. row_callback(png_structp png_ptr, png_bytep new_row,
  2322. png_uint_32 row_num, int pass)
  2323. {
  2324. /* If the image is interlaced, and you turned
  2325. on the interlace handler, this function will
  2326. be called for every row in every pass. Some
  2327. of these rows will not be changed from the
  2328. previous pass. When the row is not changed,
  2329. the new_row variable will be NULL. The rows
  2330. and passes are called in order, so you don't
  2331. really need the row_num and pass, but I'm
  2332. supplying them because it may make your life
  2333. easier.
  2334. If you did not turn on interlace handling then
  2335. the callback is called for each row of each
  2336. sub-image when the image is interlaced. In this
  2337. case 'row_num' is the row in the sub-image, not
  2338. the row in the output image as it is in all other
  2339. cases.
  2340. For the non-NULL rows of interlaced images when
  2341. you have switched on libpng interlace handling,
  2342. you must call png_progressive_combine_row()
  2343. passing in the row and the old row. You can
  2344. call this function for NULL rows (it will just
  2345. return) and for non-interlaced images (it just
  2346. does the memcpy for you) if it will make the
  2347. code easier. Thus, you can just do this for
  2348. all cases if you switch on interlace handling;
  2349. */
  2350. png_progressive_combine_row(png_ptr, old_row,
  2351. new_row);
  2352. /* where old_row is what was displayed for
  2353. previously for the row. Note that the first
  2354. pass (pass == 0, really) will completely cover
  2355. the old row, so the rows do not have to be
  2356. initialized. After the first pass (and only
  2357. for interlaced images), you will have to pass
  2358. the current row, and the function will combine
  2359. the old row and the new row.
  2360. You can also call png_process_data_pause in this
  2361. callback - see above.
  2362. */
  2363. }
  2364. void
  2365. end_callback(png_structp png_ptr, png_infop info)
  2366. {
  2367. /* This function is called after the whole image
  2368. has been read, including any chunks after the
  2369. image (up to and including the IEND). You
  2370. will usually have the same info chunk as you
  2371. had in the header, although some data may have
  2372. been added to the comments and time fields.
  2373. Most people won't do much here, perhaps setting
  2374. a flag that marks the image as finished.
  2375. */
  2376. }
  2377. .SH IV. Writing
  2378. Much of this is very similar to reading. However, everything of
  2379. importance is repeated here, so you won't have to constantly look
  2380. back up in the reading section to understand writing.
  2381. .SS Setup
  2382. You will want to do the I/O initialization before you get into libpng,
  2383. so if it doesn't work, you don't have anything to undo. If you are not
  2384. using the standard I/O functions, you will need to replace them with
  2385. custom writing functions. See the discussion under Customizing libpng.
  2386. FILE *fp = fopen(file_name, "wb");
  2387. if (!fp)
  2388. return (ERROR);
  2389. Next, png_struct and png_info need to be allocated and initialized.
  2390. As these can be both relatively large, you may not want to store these
  2391. on the stack, unless you have stack space to spare. Of course, you
  2392. will want to check if they return NULL. If you are also reading,
  2393. you won't want to name your read structure and your write structure
  2394. both "png_ptr"; you can call them anything you like, such as
  2395. "read_ptr" and "write_ptr". Look at pngtest.c, for example.
  2396. png_structp png_ptr = png_create_write_struct
  2397. (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
  2398. user_error_fn, user_warning_fn);
  2399. if (!png_ptr)
  2400. return (ERROR);
  2401. png_infop info_ptr = png_create_info_struct(png_ptr);
  2402. if (!info_ptr)
  2403. {
  2404. png_destroy_write_struct(&png_ptr,
  2405. (png_infopp)NULL);
  2406. return (ERROR);
  2407. }
  2408. If you want to use your own memory allocation routines,
  2409. define PNG_USER_MEM_SUPPORTED and use
  2410. png_create_write_struct_2() instead of png_create_write_struct():
  2411. png_structp png_ptr = png_create_write_struct_2
  2412. (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
  2413. user_error_fn, user_warning_fn, (png_voidp)
  2414. user_mem_ptr, user_malloc_fn, user_free_fn);
  2415. After you have these structures, you will need to set up the
  2416. error handling. When libpng encounters an error, it expects to
  2417. longjmp() back to your routine. Therefore, you will need to call
  2418. setjmp() and pass the png_jmpbuf(png_ptr). If you
  2419. write the file from different routines, you will need to update
  2420. the png_jmpbuf(png_ptr) every time you enter a new routine that will
  2421. call a png_*() function. See your documentation of setjmp/longjmp
  2422. for your compiler for more information on setjmp/longjmp. See
  2423. the discussion on libpng error handling in the Customizing Libpng
  2424. section below for more information on the libpng error handling.
  2425. if (setjmp(png_jmpbuf(png_ptr)))
  2426. {
  2427. png_destroy_write_struct(&png_ptr, &info_ptr);
  2428. fclose(fp);
  2429. return (ERROR);
  2430. }
  2431. ...
  2432. return;
  2433. If you would rather avoid the complexity of setjmp/longjmp issues,
  2434. you can compile libpng with PNG_NO_SETJMP, in which case
  2435. errors will result in a call to PNG_ABORT() which defaults to abort().
  2436. You can #define PNG_ABORT() to a function that does something
  2437. more useful than abort(), as long as your function does not
  2438. return.
  2439. Now you need to set up the output code. The default for libpng is to
  2440. use the C function fwrite(). If you use this, you will need to pass a
  2441. valid FILE * in the function png_init_io(). Be sure that the file is
  2442. opened in binary mode. Again, if you wish to handle writing data in
  2443. another way, see the discussion on libpng I/O handling in the Customizing
  2444. Libpng section below.
  2445. png_init_io(png_ptr, fp);
  2446. If you are embedding your PNG into a datastream such as MNG, and don't
  2447. want libpng to write the 8-byte signature, or if you have already
  2448. written the signature in your application, use
  2449. png_set_sig_bytes(png_ptr, 8);
  2450. to inform libpng that it should not write a signature.
  2451. .SS Write callbacks
  2452. At this point, you can set up a callback function that will be
  2453. called after each row has been written, which you can use to control
  2454. a progress meter or the like. It's demonstrated in pngtest.c.
  2455. You must supply a function
  2456. void write_row_callback(png_structp png_ptr, png_uint_32 row,
  2457. int pass);
  2458. {
  2459. /* put your code here */
  2460. }
  2461. (You can give it another name that you like instead of "write_row_callback")
  2462. To inform libpng about your function, use
  2463. png_set_write_status_fn(png_ptr, write_row_callback);
  2464. When this function is called the row has already been completely processed and
  2465. it has also been written out. The 'row' and 'pass' refer to the next row to be
  2466. handled. For the
  2467. non-interlaced case the row that was just handled is simply one less than the
  2468. passed in row number, and pass will always be 0. For the interlaced case the
  2469. same applies unless the row value is 0, in which case the row just handled was
  2470. the last one from one of the preceding passes. Because interlacing may skip a
  2471. pass you cannot be sure that the preceding pass is just 'pass-1', if you really
  2472. need to know what the last pass is record (row,pass) from the callback and use
  2473. the last recorded value each time.
  2474. As with the user transform you can find the output row using the
  2475. PNG_ROW_FROM_PASS_ROW macro.
  2476. You now have the option of modifying how the compression library will
  2477. run. The following functions are mainly for testing, but may be useful
  2478. in some cases, like if you need to write PNG files extremely fast and
  2479. are willing to give up some compression, or if you want to get the
  2480. maximum possible compression at the expense of slower writing. If you
  2481. have no special needs in this area, let the library do what it wants by
  2482. not calling this function at all, as it has been tuned to deliver a good
  2483. speed/compression ratio. The second parameter to png_set_filter() is
  2484. the filter method, for which the only valid values are 0 (as of the
  2485. July 1999 PNG specification, version 1.2) or 64 (if you are writing
  2486. a PNG datastream that is to be embedded in a MNG datastream). The third
  2487. parameter is a flag that indicates which filter type(s) are to be tested
  2488. for each scanline. See the PNG specification for details on the specific
  2489. filter types.
  2490. /* turn on or off filtering, and/or choose
  2491. specific filters. You can use either a single
  2492. PNG_FILTER_VALUE_NAME or the bitwise OR of one
  2493. or more PNG_FILTER_NAME masks.
  2494. */
  2495. png_set_filter(png_ptr, 0,
  2496. PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
  2497. PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
  2498. PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
  2499. PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
  2500. PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
  2501. PNG_ALL_FILTERS);
  2502. If an application wants to start and stop using particular filters during
  2503. compression, it should start out with all of the filters (to ensure that
  2504. the previous row of pixels will be stored in case it's needed later),
  2505. and then add and remove them after the start of compression.
  2506. If you are writing a PNG datastream that is to be embedded in a MNG
  2507. datastream, the second parameter can be either 0 or 64.
  2508. The png_set_compression_*() functions interface to the zlib compression
  2509. library, and should mostly be ignored unless you really know what you are
  2510. doing. The only generally useful call is png_set_compression_level()
  2511. which changes how much time zlib spends on trying to compress the image
  2512. data. See the Compression Library (zlib.h and algorithm.txt, distributed
  2513. with zlib) for details on the compression levels.
  2514. #include zlib.h
  2515. /* Set the zlib compression level */
  2516. png_set_compression_level(png_ptr,
  2517. Z_BEST_COMPRESSION);
  2518. /* Set other zlib parameters for compressing IDAT */
  2519. png_set_compression_mem_level(png_ptr, 8);
  2520. png_set_compression_strategy(png_ptr,
  2521. Z_DEFAULT_STRATEGY);
  2522. png_set_compression_window_bits(png_ptr, 15);
  2523. png_set_compression_method(png_ptr, 8);
  2524. png_set_compression_buffer_size(png_ptr, 8192)
  2525. /* Set zlib parameters for text compression
  2526. * If you don't call these, the parameters
  2527. * fall back on those defined for IDAT chunks
  2528. */
  2529. png_set_text_compression_mem_level(png_ptr, 8);
  2530. png_set_text_compression_strategy(png_ptr,
  2531. Z_DEFAULT_STRATEGY);
  2532. png_set_text_compression_window_bits(png_ptr, 15);
  2533. png_set_text_compression_method(png_ptr, 8);
  2534. .SS Setting the contents of info for output
  2535. You now need to fill in the png_info structure with all the data you
  2536. wish to write before the actual image. Note that the only thing you
  2537. are allowed to write after the image is the text chunks and the time
  2538. chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
  2539. the latest PNG specification for more information on that. If you
  2540. wish to write them before the image, fill them in now, and flag that
  2541. data as being valid. If you want to wait until after the data, don't
  2542. fill them until png_write_end(). For all the fields in png_info and
  2543. their data types, see png.h. For explanations of what the fields
  2544. contain, see the PNG specification.
  2545. Some of the more important parts of the png_info are:
  2546. png_set_IHDR(png_ptr, info_ptr, width, height,
  2547. bit_depth, color_type, interlace_type,
  2548. compression_type, filter_method)
  2549. width - holds the width of the image
  2550. in pixels (up to 2^31).
  2551. height - holds the height of the image
  2552. in pixels (up to 2^31).
  2553. bit_depth - holds the bit depth of one of the
  2554. image channels.
  2555. (valid values are 1, 2, 4, 8, 16
  2556. and depend also on the
  2557. color_type. See also significant
  2558. bits (sBIT) below).
  2559. color_type - describes which color/alpha
  2560. channels are present.
  2561. PNG_COLOR_TYPE_GRAY
  2562. (bit depths 1, 2, 4, 8, 16)
  2563. PNG_COLOR_TYPE_GRAY_ALPHA
  2564. (bit depths 8, 16)
  2565. PNG_COLOR_TYPE_PALETTE
  2566. (bit depths 1, 2, 4, 8)
  2567. PNG_COLOR_TYPE_RGB
  2568. (bit_depths 8, 16)
  2569. PNG_COLOR_TYPE_RGB_ALPHA
  2570. (bit_depths 8, 16)
  2571. PNG_COLOR_MASK_PALETTE
  2572. PNG_COLOR_MASK_COLOR
  2573. PNG_COLOR_MASK_ALPHA
  2574. interlace_type - PNG_INTERLACE_NONE or
  2575. PNG_INTERLACE_ADAM7
  2576. compression_type - (must be
  2577. PNG_COMPRESSION_TYPE_DEFAULT)
  2578. filter_method - (must be PNG_FILTER_TYPE_DEFAULT
  2579. or, if you are writing a PNG to
  2580. be embedded in a MNG datastream,
  2581. can also be
  2582. PNG_INTRAPIXEL_DIFFERENCING)
  2583. If you call png_set_IHDR(), the call must appear before any of the
  2584. other png_set_*() functions, because they might require access to some of
  2585. the IHDR settings. The remaining png_set_*() functions can be called
  2586. in any order.
  2587. If you wish, you can reset the compression_type, interlace_type, or
  2588. filter_method later by calling png_set_IHDR() again; if you do this, the
  2589. width, height, bit_depth, and color_type must be the same in each call.
  2590. png_set_PLTE(png_ptr, info_ptr, palette,
  2591. num_palette);
  2592. palette - the palette for the file
  2593. (array of png_color)
  2594. num_palette - number of entries in the palette
  2595. png_set_gAMA(png_ptr, info_ptr, file_gamma);
  2596. png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
  2597. file_gamma - the gamma at which the image was
  2598. created (PNG_INFO_gAMA)
  2599. int_file_gamma - 100,000 times the gamma at which
  2600. the image was created
  2601. png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
  2602. green_x, green_y, blue_x, blue_y)
  2603. png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
  2604. green_Y, green_Z, blue_X, blue_Y, blue_Z)
  2605. png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
  2606. int_red_x, int_red_y, int_green_x, int_green_y,
  2607. int_blue_x, int_blue_y)
  2608. png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
  2609. int_red_Z, int_green_X, int_green_Y, int_green_Z,
  2610. int_blue_X, int_blue_Y, int_blue_Z)
  2611. {white,red,green,blue}_{x,y}
  2612. A color space encoding specified using the chromaticities
  2613. of the end points and the white point.
  2614. {red,green,blue}_{X,Y,Z}
  2615. A color space encoding specified using the encoding end
  2616. points - the CIE tristimulus specification of the intended
  2617. color of the red, green and blue channels in the PNG RGB
  2618. data. The white point is simply the sum of the three end
  2619. points.
  2620. png_set_sRGB(png_ptr, info_ptr, srgb_intent);
  2621. srgb_intent - the rendering intent
  2622. (PNG_INFO_sRGB) The presence of
  2623. the sRGB chunk means that the pixel
  2624. data is in the sRGB color space.
  2625. This chunk also implies specific
  2626. values of gAMA and cHRM. Rendering
  2627. intent is the CSS-1 property that
  2628. has been defined by the International
  2629. Color Consortium
  2630. (http://www.color.org).
  2631. It can be one of
  2632. PNG_sRGB_INTENT_SATURATION,
  2633. PNG_sRGB_INTENT_PERCEPTUAL,
  2634. PNG_sRGB_INTENT_ABSOLUTE, or
  2635. PNG_sRGB_INTENT_RELATIVE.
  2636. png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
  2637. srgb_intent);
  2638. srgb_intent - the rendering intent
  2639. (PNG_INFO_sRGB) The presence of the
  2640. sRGB chunk means that the pixel
  2641. data is in the sRGB color space.
  2642. This function also causes gAMA and
  2643. cHRM chunks with the specific values
  2644. that are consistent with sRGB to be
  2645. written.
  2646. png_set_iCCP(png_ptr, info_ptr, name, compression_type,
  2647. profile, proflen);
  2648. name - The profile name.
  2649. compression_type - The compression type; always
  2650. PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
  2651. You may give NULL to this argument to
  2652. ignore it.
  2653. profile - International Color Consortium color
  2654. profile data. May contain NULs.
  2655. proflen - length of profile data in bytes.
  2656. png_set_sBIT(png_ptr, info_ptr, sig_bit);
  2657. sig_bit - the number of significant bits for
  2658. (PNG_INFO_sBIT) each of the gray, red,
  2659. green, and blue channels, whichever are
  2660. appropriate for the given color type
  2661. (png_color_16)
  2662. png_set_tRNS(png_ptr, info_ptr, trans_alpha,
  2663. num_trans, trans_color);
  2664. trans_alpha - array of alpha (transparency)
  2665. entries for palette (PNG_INFO_tRNS)
  2666. num_trans - number of transparent entries
  2667. (PNG_INFO_tRNS)
  2668. trans_color - graylevel or color sample values
  2669. (in order red, green, blue) of the
  2670. single transparent color for
  2671. non-paletted images (PNG_INFO_tRNS)
  2672. png_set_hIST(png_ptr, info_ptr, hist);
  2673. hist - histogram of palette (array of
  2674. png_uint_16) (PNG_INFO_hIST)
  2675. png_set_tIME(png_ptr, info_ptr, mod_time);
  2676. mod_time - time image was last modified
  2677. (PNG_VALID_tIME)
  2678. png_set_bKGD(png_ptr, info_ptr, background);
  2679. background - background color (of type
  2680. png_color_16p) (PNG_VALID_bKGD)
  2681. png_set_text(png_ptr, info_ptr, text_ptr, num_text);
  2682. text_ptr - array of png_text holding image
  2683. comments
  2684. text_ptr[i].compression - type of compression used
  2685. on "text" PNG_TEXT_COMPRESSION_NONE
  2686. PNG_TEXT_COMPRESSION_zTXt
  2687. PNG_ITXT_COMPRESSION_NONE
  2688. PNG_ITXT_COMPRESSION_zTXt
  2689. text_ptr[i].key - keyword for comment. Must contain
  2690. 1-79 characters.
  2691. text_ptr[i].text - text comments for current
  2692. keyword. Can be NULL or empty.
  2693. text_ptr[i].text_length - length of text string,
  2694. after decompression, 0 for iTXt
  2695. text_ptr[i].itxt_length - length of itxt string,
  2696. after decompression, 0 for tEXt/zTXt
  2697. text_ptr[i].lang - language of comment (NULL or
  2698. empty for unknown).
  2699. text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
  2700. or empty for unknown).
  2701. Note that the itxt_length, lang, and lang_key
  2702. members of the text_ptr structure only exist when the
  2703. library is built with iTXt chunk support. Prior to
  2704. libpng-1.4.0 the library was built by default without
  2705. iTXt support. Also note that when iTXt is supported,
  2706. they contain NULL pointers when the "compression"
  2707. field contains PNG_TEXT_COMPRESSION_NONE or
  2708. PNG_TEXT_COMPRESSION_zTXt.
  2709. num_text - number of comments
  2710. png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
  2711. num_spalettes);
  2712. palette_ptr - array of png_sPLT_struct structures
  2713. to be added to the list of palettes
  2714. in the info structure.
  2715. num_spalettes - number of palette structures to be
  2716. added.
  2717. png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
  2718. unit_type);
  2719. offset_x - positive offset from the left
  2720. edge of the screen
  2721. offset_y - positive offset from the top
  2722. edge of the screen
  2723. unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
  2724. png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
  2725. unit_type);
  2726. res_x - pixels/unit physical resolution
  2727. in x direction
  2728. res_y - pixels/unit physical resolution
  2729. in y direction
  2730. unit_type - PNG_RESOLUTION_UNKNOWN,
  2731. PNG_RESOLUTION_METER
  2732. png_set_sCAL(png_ptr, info_ptr, unit, width, height)
  2733. unit - physical scale units (an integer)
  2734. width - width of a pixel in physical scale units
  2735. height - height of a pixel in physical scale units
  2736. (width and height are doubles)
  2737. png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
  2738. unit - physical scale units (an integer)
  2739. width - width of a pixel in physical scale units
  2740. expressed as a string
  2741. height - height of a pixel in physical scale units
  2742. (width and height are strings like "2.54")
  2743. png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
  2744. num_unknowns)
  2745. unknowns - array of png_unknown_chunk
  2746. structures holding unknown chunks
  2747. unknowns[i].name - name of unknown chunk
  2748. unknowns[i].data - data of unknown chunk
  2749. unknowns[i].size - size of unknown chunk's data
  2750. unknowns[i].location - position to write chunk in file
  2751. 0: do not write chunk
  2752. PNG_HAVE_IHDR: before PLTE
  2753. PNG_HAVE_PLTE: before IDAT
  2754. PNG_AFTER_IDAT: after IDAT
  2755. The "location" member is set automatically according to
  2756. what part of the output file has already been written.
  2757. You can change its value after calling png_set_unknown_chunks()
  2758. as demonstrated in pngtest.c. Within each of the "locations",
  2759. the chunks are sequenced according to their position in the
  2760. structure (that is, the value of "i", which is the order in which
  2761. the chunk was either read from the input file or defined with
  2762. png_set_unknown_chunks).
  2763. A quick word about text and num_text. text is an array of png_text
  2764. structures. num_text is the number of valid structures in the array.
  2765. Each png_text structure holds a language code, a keyword, a text value,
  2766. and a compression type.
  2767. The compression types have the same valid numbers as the compression
  2768. types of the image data. Currently, the only valid number is zero.
  2769. However, you can store text either compressed or uncompressed, unlike
  2770. images, which always have to be compressed. So if you don't want the
  2771. text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
  2772. Because tEXt and zTXt chunks don't have a language field, if you
  2773. specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
  2774. any language code or translated keyword will not be written out.
  2775. Until text gets around a few hundred bytes, it is not worth compressing it.
  2776. After the text has been written out to the file, the compression type
  2777. is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
  2778. so that it isn't written out again at the end (in case you are calling
  2779. png_write_end() with the same struct).
  2780. The keywords that are given in the PNG Specification are:
  2781. Title Short (one line) title or
  2782. caption for image
  2783. Author Name of image's creator
  2784. Description Description of image (possibly long)
  2785. Copyright Copyright notice
  2786. Creation Time Time of original image creation
  2787. (usually RFC 1123 format, see below)
  2788. Software Software used to create the image
  2789. Disclaimer Legal disclaimer
  2790. Warning Warning of nature of content
  2791. Source Device used to create the image
  2792. Comment Miscellaneous comment; conversion
  2793. from other image format
  2794. The keyword-text pairs work like this. Keywords should be short
  2795. simple descriptions of what the comment is about. Some typical
  2796. keywords are found in the PNG specification, as is some recommendations
  2797. on keywords. You can repeat keywords in a file. You can even write
  2798. some text before the image and some after. For example, you may want
  2799. to put a description of the image before the image, but leave the
  2800. disclaimer until after, so viewers working over modem connections
  2801. don't have to wait for the disclaimer to go over the modem before
  2802. they start seeing the image. Finally, keywords should be full
  2803. words, not abbreviations. Keywords and text are in the ISO 8859-1
  2804. (Latin-1) character set (a superset of regular ASCII) and can not
  2805. contain NUL characters, and should not contain control or other
  2806. unprintable characters. To make the comments widely readable, stick
  2807. with basic ASCII, and avoid machine specific character set extensions
  2808. like the IBM-PC character set. The keyword must be present, but
  2809. you can leave off the text string on non-compressed pairs.
  2810. Compressed pairs must have a text string, as only the text string
  2811. is compressed anyway, so the compression would be meaningless.
  2812. PNG supports modification time via the png_time structure. Two
  2813. conversion routines are provided, png_convert_from_time_t() for
  2814. time_t and png_convert_from_struct_tm() for struct tm. The
  2815. time_t routine uses gmtime(). You don't have to use either of
  2816. these, but if you wish to fill in the png_time structure directly,
  2817. you should provide the time in universal time (GMT) if possible
  2818. instead of your local time. Note that the year number is the full
  2819. year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
  2820. that months start with 1.
  2821. If you want to store the time of the original image creation, you should
  2822. use a plain tEXt chunk with the "Creation Time" keyword. This is
  2823. necessary because the "creation time" of a PNG image is somewhat vague,
  2824. depending on whether you mean the PNG file, the time the image was
  2825. created in a non-PNG format, a still photo from which the image was
  2826. scanned, or possibly the subject matter itself. In order to facilitate
  2827. machine-readable dates, it is recommended that the "Creation Time"
  2828. tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
  2829. although this isn't a requirement. Unlike the tIME chunk, the
  2830. "Creation Time" tEXt chunk is not expected to be automatically changed
  2831. by the software. To facilitate the use of RFC 1123 dates, a function
  2832. png_convert_to_rfc1123(png_timep) is provided to convert from PNG
  2833. time to an RFC 1123 format string.
  2834. .SS Writing unknown chunks
  2835. You can use the png_set_unknown_chunks function to queue up chunks
  2836. for writing. You give it a chunk name, raw data, and a size; that's
  2837. all there is to it. The chunks will be written by the next following
  2838. png_write_info_before_PLTE, png_write_info, or png_write_end function.
  2839. Any chunks previously read into the info structure's unknown-chunk
  2840. list will also be written out in a sequence that satisfies the PNG
  2841. specification's ordering rules.
  2842. .SS The high-level write interface
  2843. At this point there are two ways to proceed; through the high-level
  2844. write interface, or through a sequence of low-level write operations.
  2845. You can use the high-level interface if your image data is present
  2846. in the info structure. All defined output
  2847. transformations are permitted, enabled by the following masks.
  2848. PNG_TRANSFORM_IDENTITY No transformation
  2849. PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
  2850. PNG_TRANSFORM_PACKSWAP Change order of packed
  2851. pixels to LSB first
  2852. PNG_TRANSFORM_INVERT_MONO Invert monochrome images
  2853. PNG_TRANSFORM_SHIFT Normalize pixels to the
  2854. sBIT depth
  2855. PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
  2856. to BGRA
  2857. PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
  2858. to AG
  2859. PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
  2860. to transparency
  2861. PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
  2862. PNG_TRANSFORM_STRIP_FILLER Strip out filler
  2863. bytes (deprecated).
  2864. PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
  2865. filler bytes
  2866. PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
  2867. filler bytes
  2868. If you have valid image data in the info structure (you can use
  2869. png_set_rows() to put image data in the info structure), simply do this:
  2870. png_write_png(png_ptr, info_ptr, png_transforms, NULL)
  2871. where png_transforms is an integer containing the bitwise OR of some set of
  2872. transformation flags. This call is equivalent to png_write_info(),
  2873. followed the set of transformations indicated by the transform mask,
  2874. then png_write_image(), and finally png_write_end().
  2875. (The final parameter of this call is not yet used. Someday it might point
  2876. to transformation parameters required by some future output transform.)
  2877. You must use png_transforms and not call any png_set_transform() functions
  2878. when you use png_write_png().
  2879. .SS The low-level write interface
  2880. If you are going the low-level route instead, you are now ready to
  2881. write all the file information up to the actual image data. You do
  2882. this with a call to png_write_info().
  2883. png_write_info(png_ptr, info_ptr);
  2884. Note that there is one transformation you may need to do before
  2885. png_write_info(). In PNG files, the alpha channel in an image is the
  2886. level of opacity. If your data is supplied as a level of transparency,
  2887. you can invert the alpha channel before you write it, so that 0 is
  2888. fully transparent and 255 (in 8-bit or paletted images) or 65535
  2889. (in 16-bit images) is fully opaque, with
  2890. png_set_invert_alpha(png_ptr);
  2891. This must appear before png_write_info() instead of later with the
  2892. other transformations because in the case of paletted images the tRNS
  2893. chunk data has to be inverted before the tRNS chunk is written. If
  2894. your image is not a paletted image, the tRNS data (which in such cases
  2895. represents a single color to be rendered as transparent) won't need to
  2896. be changed, and you can safely do this transformation after your
  2897. png_write_info() call.
  2898. If you need to write a private chunk that you want to appear before
  2899. the PLTE chunk when PLTE is present, you can write the PNG info in
  2900. two steps, and insert code to write your own chunk between them:
  2901. png_write_info_before_PLTE(png_ptr, info_ptr);
  2902. png_set_unknown_chunks(png_ptr, info_ptr, ...);
  2903. png_write_info(png_ptr, info_ptr);
  2904. After you've written the file information, you can set up the library
  2905. to handle any special transformations of the image data. The various
  2906. ways to transform the data will be described in the order that they
  2907. should occur. This is important, as some of these change the color
  2908. type and/or bit depth of the data, and some others only work on
  2909. certain color types and bit depths. Even though each transformation
  2910. checks to see if it has data that it can do something with, you should
  2911. make sure to only enable a transformation if it will be valid for the
  2912. data. For example, don't swap red and blue on grayscale data.
  2913. PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
  2914. the library to strip input data that has 4 or 8 bytes per pixel down
  2915. to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
  2916. bytes per pixel).
  2917. png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
  2918. where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
  2919. PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
  2920. is stored XRGB or RGBX.
  2921. PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
  2922. they can, resulting in, for example, 8 pixels per byte for 1 bit files.
  2923. If the data is supplied at 1 pixel per byte, use this code, which will
  2924. correctly pack the pixels into a single byte:
  2925. png_set_packing(png_ptr);
  2926. PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
  2927. data is of another bit depth, you can write an sBIT chunk into the
  2928. file so that decoders can recover the original data if desired.
  2929. /* Set the true bit depth of the image data */
  2930. if (color_type & PNG_COLOR_MASK_COLOR)
  2931. {
  2932. sig_bit.red = true_bit_depth;
  2933. sig_bit.green = true_bit_depth;
  2934. sig_bit.blue = true_bit_depth;
  2935. }
  2936. else
  2937. {
  2938. sig_bit.gray = true_bit_depth;
  2939. }
  2940. if (color_type & PNG_COLOR_MASK_ALPHA)
  2941. {
  2942. sig_bit.alpha = true_bit_depth;
  2943. }
  2944. png_set_sBIT(png_ptr, info_ptr, &sig_bit);
  2945. If the data is stored in the row buffer in a bit depth other than
  2946. one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
  2947. this will scale the values to appear to be the correct bit depth as
  2948. is required by PNG.
  2949. png_set_shift(png_ptr, &sig_bit);
  2950. PNG files store 16-bit pixels in network byte order (big-endian,
  2951. ie. most significant bits first). This code would be used if they are
  2952. supplied the other way (little-endian, i.e. least significant bits
  2953. first, the way PCs store them):
  2954. if (bit_depth > 8)
  2955. png_set_swap(png_ptr);
  2956. If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
  2957. need to change the order the pixels are packed into bytes, you can use:
  2958. if (bit_depth < 8)
  2959. png_set_packswap(png_ptr);
  2960. PNG files store 3 color pixels in red, green, blue order. This code
  2961. would be used if they are supplied as blue, green, red:
  2962. png_set_bgr(png_ptr);
  2963. PNG files describe monochrome as black being zero and white being
  2964. one. This code would be used if the pixels are supplied with this reversed
  2965. (black being one and white being zero):
  2966. png_set_invert_mono(png_ptr);
  2967. Finally, you can write your own transformation function if none of
  2968. the existing ones meets your needs. This is done by setting a callback
  2969. with
  2970. png_set_write_user_transform_fn(png_ptr,
  2971. write_transform_fn);
  2972. You must supply the function
  2973. void write_transform_fn(png_structp png_ptr, png_row_infop
  2974. row_info, png_bytep data)
  2975. See pngtest.c for a working example. Your function will be called
  2976. before any of the other transformations are processed. If supported
  2977. libpng also supplies an information routine that may be called from
  2978. your callback:
  2979. png_get_current_row_number(png_ptr);
  2980. png_get_current_pass_number(png_ptr);
  2981. This returns the current row passed to the transform. With interlaced
  2982. images the value returned is the row in the input sub-image image. Use
  2983. PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
  2984. find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
  2985. The discussion of interlace handling above contains more information on how to
  2986. use these values.
  2987. You can also set up a pointer to a user structure for use by your
  2988. callback function.
  2989. png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
  2990. The user_channels and user_depth parameters of this function are ignored
  2991. when writing; you can set them to zero as shown.
  2992. You can retrieve the pointer via the function png_get_user_transform_ptr().
  2993. For example:
  2994. voidp write_user_transform_ptr =
  2995. png_get_user_transform_ptr(png_ptr);
  2996. It is possible to have libpng flush any pending output, either manually,
  2997. or automatically after a certain number of lines have been written. To
  2998. flush the output stream a single time call:
  2999. png_write_flush(png_ptr);
  3000. and to have libpng flush the output stream periodically after a certain
  3001. number of scanlines have been written, call:
  3002. png_set_flush(png_ptr, nrows);
  3003. Note that the distance between rows is from the last time png_write_flush()
  3004. was called, or the first row of the image if it has never been called.
  3005. So if you write 50 lines, and then png_set_flush 25, it will flush the
  3006. output on the next scanline, and every 25 lines thereafter, unless
  3007. png_write_flush() is called before 25 more lines have been written.
  3008. If nrows is too small (less than about 10 lines for a 640 pixel wide
  3009. RGB image) the image compression may decrease noticeably (although this
  3010. may be acceptable for real-time applications). Infrequent flushing will
  3011. only degrade the compression performance by a few percent over images
  3012. that do not use flushing.
  3013. .SS Writing the image data
  3014. That's it for the transformations. Now you can write the image data.
  3015. The simplest way to do this is in one function call. If you have the
  3016. whole image in memory, you can just call png_write_image() and libpng
  3017. will write the image. You will need to pass in an array of pointers to
  3018. each row. This function automatically handles interlacing, so you don't
  3019. need to call png_set_interlace_handling() or call this function multiple
  3020. times, or any of that other stuff necessary with png_write_rows().
  3021. png_write_image(png_ptr, row_pointers);
  3022. where row_pointers is:
  3023. png_byte *row_pointers[height];
  3024. You can point to void or char or whatever you use for pixels.
  3025. If you don't want to write the whole image at once, you can
  3026. use png_write_rows() instead. If the file is not interlaced,
  3027. this is simple:
  3028. png_write_rows(png_ptr, row_pointers,
  3029. number_of_rows);
  3030. row_pointers is the same as in the png_write_image() call.
  3031. If you are just writing one row at a time, you can do this with
  3032. a single row_pointer instead of an array of row_pointers:
  3033. png_bytep row_pointer = row;
  3034. png_write_row(png_ptr, row_pointer);
  3035. When the file is interlaced, things can get a good deal more complicated.
  3036. The only currently (as of the PNG Specification version 1.2, dated July
  3037. 1999) defined interlacing scheme for PNG files is the "Adam7" interlace
  3038. scheme, that breaks down an image into seven smaller images of varying
  3039. size. libpng will build these images for you, or you can do them
  3040. yourself. If you want to build them yourself, see the PNG specification
  3041. for details of which pixels to write when.
  3042. If you don't want libpng to handle the interlacing details, just
  3043. use png_set_interlace_handling() and call png_write_rows() the
  3044. correct number of times to write all the sub-images
  3045. (png_set_interlace_handling() returns the number of sub-images.)
  3046. If you want libpng to build the sub-images, call this before you start
  3047. writing any rows:
  3048. number_of_passes = png_set_interlace_handling(png_ptr);
  3049. This will return the number of passes needed. Currently, this is seven,
  3050. but may change if another interlace type is added.
  3051. Then write the complete image number_of_passes times.
  3052. png_write_rows(png_ptr, row_pointers, number_of_rows);
  3053. Think carefully before you write an interlaced image. Typically code that
  3054. reads such images reads all the image data into memory, uncompressed, before
  3055. doing any processing. Only code that can display an image on the fly can
  3056. take advantage of the interlacing and even then the image has to be exactly
  3057. the correct size for the output device, because scaling an image requires
  3058. adjacent pixels and these are not available until all the passes have been
  3059. read.
  3060. If you do write an interlaced image you will hardly ever need to handle
  3061. the interlacing yourself. Call png_set_interlace_handling() and use the
  3062. approach described above.
  3063. The only time it is conceivable that you will really need to write an
  3064. interlaced image pass-by-pass is when you have read one pass by pass and
  3065. made some pixel-by-pixel transformation to it, as described in the read
  3066. code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
  3067. to determine the size of each sub-image in turn and simply write the rows
  3068. you obtained from the read code.
  3069. .SS Finishing a sequential write
  3070. After you are finished writing the image, you should finish writing
  3071. the file. If you are interested in writing comments or time, you should
  3072. pass an appropriately filled png_info pointer. If you are not interested,
  3073. you can pass NULL.
  3074. png_write_end(png_ptr, info_ptr);
  3075. When you are done, you can free all memory used by libpng like this:
  3076. png_destroy_write_struct(&png_ptr, &info_ptr);
  3077. It is also possible to individually free the info_ptr members that
  3078. point to libpng-allocated storage with the following function:
  3079. png_free_data(png_ptr, info_ptr, mask, seq)
  3080. mask - identifies data to be freed, a mask
  3081. containing the bitwise OR of one or
  3082. more of
  3083. PNG_FREE_PLTE, PNG_FREE_TRNS,
  3084. PNG_FREE_HIST, PNG_FREE_ICCP,
  3085. PNG_FREE_PCAL, PNG_FREE_ROWS,
  3086. PNG_FREE_SCAL, PNG_FREE_SPLT,
  3087. PNG_FREE_TEXT, PNG_FREE_UNKN,
  3088. or simply PNG_FREE_ALL
  3089. seq - sequence number of item to be freed
  3090. (-1 for all items)
  3091. This function may be safely called when the relevant storage has
  3092. already been freed, or has not yet been allocated, or was allocated
  3093. by the user and not by libpng, and will in those cases do nothing.
  3094. The "seq" parameter is ignored if only one item of the selected data
  3095. type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
  3096. are allowed for the data type identified in the mask, such as text or
  3097. sPLT, only the n'th item in the structure is freed, where n is "seq".
  3098. If you allocated data such as a palette that you passed in to libpng
  3099. with png_set_*, you must not free it until just before the call to
  3100. png_destroy_write_struct().
  3101. The default behavior is only to free data that was allocated internally
  3102. by libpng. This can be changed, so that libpng will not free the data,
  3103. or so that it will free data that was allocated by the user with png_malloc()
  3104. or png_zalloc() and passed in via a png_set_*() function, with
  3105. png_data_freer(png_ptr, info_ptr, freer, mask)
  3106. freer - one of
  3107. PNG_DESTROY_WILL_FREE_DATA
  3108. PNG_SET_WILL_FREE_DATA
  3109. PNG_USER_WILL_FREE_DATA
  3110. mask - which data elements are affected
  3111. same choices as in png_free_data()
  3112. For example, to transfer responsibility for some data from a read structure
  3113. to a write structure, you could use
  3114. png_data_freer(read_ptr, read_info_ptr,
  3115. PNG_USER_WILL_FREE_DATA,
  3116. PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
  3117. png_data_freer(write_ptr, write_info_ptr,
  3118. PNG_DESTROY_WILL_FREE_DATA,
  3119. PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
  3120. thereby briefly reassigning responsibility for freeing to the user but
  3121. immediately afterwards reassigning it once more to the write_destroy
  3122. function. Having done this, it would then be safe to destroy the read
  3123. structure and continue to use the PLTE, tRNS, and hIST data in the write
  3124. structure.
  3125. This function only affects data that has already been allocated.
  3126. You can call this function before calling after the png_set_*() functions
  3127. to control whether the user or png_destroy_*() is supposed to free the data.
  3128. When the user assumes responsibility for libpng-allocated data, the
  3129. application must use
  3130. png_free() to free it, and when the user transfers responsibility to libpng
  3131. for data that the user has allocated, the user must have used png_malloc()
  3132. or png_zalloc() to allocate it.
  3133. If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
  3134. separately, do not transfer responsibility for freeing text_ptr to libpng,
  3135. because when libpng fills a png_text structure it combines these members with
  3136. the key member, and png_free_data() will free only text_ptr.key. Similarly,
  3137. if you transfer responsibility for free'ing text_ptr from libpng to your
  3138. application, your application must not separately free those members.
  3139. For a more compact example of writing a PNG image, see the file example.c.
  3140. .SH V. Modifying/Customizing libpng:
  3141. There are two issues here. The first is changing how libpng does
  3142. standard things like memory allocation, input/output, and error handling.
  3143. The second deals with more complicated things like adding new chunks,
  3144. adding new transformations, and generally changing how libpng works.
  3145. Both of those are compile-time issues; that is, they are generally
  3146. determined at the time the code is written, and there is rarely a need
  3147. to provide the user with a means of changing them.
  3148. Memory allocation, input/output, and error handling
  3149. All of the memory allocation, input/output, and error handling in libpng
  3150. goes through callbacks that are user-settable. The default routines are
  3151. in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
  3152. these functions, call the appropriate png_set_*_fn() function.
  3153. Memory allocation is done through the functions png_malloc(), png_calloc(),
  3154. and png_free(). These currently just call the standard C functions.
  3155. png_calloc() calls png_malloc() and then clears the newly
  3156. allocated memory to zero. There is limited support for certain systems
  3157. with segmented memory architectures and the types of pointers declared by
  3158. png.h match this; you will have to use appropriate pointers in your
  3159. application. Since it is
  3160. unlikely that the method of handling memory allocation on a platform
  3161. will change between applications, these functions must be modified in
  3162. the library at compile time. If you prefer to use a different method
  3163. of allocating and freeing data, you can use png_create_read_struct_2() or
  3164. png_create_write_struct_2() to register your own functions as described
  3165. above. These functions also provide a void pointer that can be retrieved
  3166. via
  3167. mem_ptr=png_get_mem_ptr(png_ptr);
  3168. Your replacement memory functions must have prototypes as follows:
  3169. png_voidp malloc_fn(png_structp png_ptr,
  3170. png_alloc_size_t size);
  3171. void free_fn(png_structp png_ptr, png_voidp ptr);
  3172. Your malloc_fn() must return NULL in case of failure. The png_malloc()
  3173. function will normally call png_error() if it receives a NULL from the
  3174. system memory allocator or from your replacement malloc_fn().
  3175. Your free_fn() will never be called with a NULL ptr, since libpng's
  3176. png_free() checks for NULL before calling free_fn().
  3177. Input/Output in libpng is done through png_read() and png_write(),
  3178. which currently just call fread() and fwrite(). The FILE * is stored in
  3179. png_struct and is initialized via png_init_io(). If you wish to change
  3180. the method of I/O, the library supplies callbacks that you can set
  3181. through the function png_set_read_fn() and png_set_write_fn() at run
  3182. time, instead of calling the png_init_io() function. These functions
  3183. also provide a void pointer that can be retrieved via the function
  3184. png_get_io_ptr(). For example:
  3185. png_set_read_fn(png_structp read_ptr,
  3186. voidp read_io_ptr, png_rw_ptr read_data_fn)
  3187. png_set_write_fn(png_structp write_ptr,
  3188. voidp write_io_ptr, png_rw_ptr write_data_fn,
  3189. png_flush_ptr output_flush_fn);
  3190. voidp read_io_ptr = png_get_io_ptr(read_ptr);
  3191. voidp write_io_ptr = png_get_io_ptr(write_ptr);
  3192. The replacement I/O functions must have prototypes as follows:
  3193. void user_read_data(png_structp png_ptr,
  3194. png_bytep data, png_size_t length);
  3195. void user_write_data(png_structp png_ptr,
  3196. png_bytep data, png_size_t length);
  3197. void user_flush_data(png_structp png_ptr);
  3198. The user_read_data() function is responsible for detecting and
  3199. handling end-of-data errors.
  3200. Supplying NULL for the read, write, or flush functions sets them back
  3201. to using the default C stream functions, which expect the io_ptr to
  3202. point to a standard *FILE structure. It is probably a mistake
  3203. to use NULL for one of write_data_fn and output_flush_fn but not both
  3204. of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
  3205. It is an error to read from a write stream, and vice versa.
  3206. Error handling in libpng is done through png_error() and png_warning().
  3207. Errors handled through png_error() are fatal, meaning that png_error()
  3208. should never return to its caller. Currently, this is handled via
  3209. setjmp() and longjmp() (unless you have compiled libpng with
  3210. PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
  3211. but you could change this to do things like exit() if you should wish,
  3212. as long as your function does not return.
  3213. On non-fatal errors, png_warning() is called
  3214. to print a warning message, and then control returns to the calling code.
  3215. By default png_error() and png_warning() print a message on stderr via
  3216. fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
  3217. (because you don't want the messages) or PNG_NO_STDIO defined (because
  3218. fprintf() isn't available). If you wish to change the behavior of the error
  3219. functions, you will need to set up your own message callbacks. These
  3220. functions are normally supplied at the time that the png_struct is created.
  3221. It is also possible to redirect errors and warnings to your own replacement
  3222. functions after png_create_*_struct() has been called by calling:
  3223. png_set_error_fn(png_structp png_ptr,
  3224. png_voidp error_ptr, png_error_ptr error_fn,
  3225. png_error_ptr warning_fn);
  3226. png_voidp error_ptr = png_get_error_ptr(png_ptr);
  3227. If NULL is supplied for either error_fn or warning_fn, then the libpng
  3228. default function will be used, calling fprintf() and/or longjmp() if a
  3229. problem is encountered. The replacement error functions should have
  3230. parameters as follows:
  3231. void user_error_fn(png_structp png_ptr,
  3232. png_const_charp error_msg);
  3233. void user_warning_fn(png_structp png_ptr,
  3234. png_const_charp warning_msg);
  3235. The motivation behind using setjmp() and longjmp() is the C++ throw and
  3236. catch exception handling methods. This makes the code much easier to write,
  3237. as there is no need to check every return code of every function call.
  3238. However, there are some uncertainties about the status of local variables
  3239. after a longjmp, so the user may want to be careful about doing anything
  3240. after setjmp returns non-zero besides returning itself. Consult your
  3241. compiler documentation for more details. For an alternative approach, you
  3242. may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net),
  3243. which is illustrated in pngvalid.c and in contrib/visupng.
  3244. .SS Custom chunks
  3245. If you need to read or write custom chunks, you may need to get deeper
  3246. into the libpng code. The library now has mechanisms for storing
  3247. and writing chunks of unknown type; you can even declare callbacks
  3248. for custom chunks. However, this may not be good enough if the
  3249. library code itself needs to know about interactions between your
  3250. chunk and existing `intrinsic' chunks.
  3251. If you need to write a new intrinsic chunk, first read the PNG
  3252. specification. Acquire a first level of understanding of how it works.
  3253. Pay particular attention to the sections that describe chunk names,
  3254. and look at how other chunks were designed, so you can do things
  3255. similarly. Second, check out the sections of libpng that read and
  3256. write chunks. Try to find a chunk that is similar to yours and use
  3257. it as a template. More details can be found in the comments inside
  3258. the code. It is best to handle private or unknown chunks in a generic method,
  3259. via callback functions, instead of by modifying libpng functions. This
  3260. is illustrated in pngtest.c, which uses a callback function to handle a
  3261. private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
  3262. libpng.
  3263. If you wish to write your own transformation for the data, look through
  3264. the part of the code that does the transformations, and check out some of
  3265. the simpler ones to get an idea of how they work. Try to find a similar
  3266. transformation to the one you want to add and copy off of it. More details
  3267. can be found in the comments inside the code itself.
  3268. .SS Configuring for 16-bit platforms
  3269. You will want to look into zconf.h to tell zlib (and thus libpng) that
  3270. it cannot allocate more then 64K at a time. Even if you can, the memory
  3271. won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
  3272. .SS Configuring for DOS
  3273. For DOS users who only have access to the lower 640K, you will
  3274. have to limit zlib's memory usage via a png_set_compression_mem_level()
  3275. call. See zlib.h or zconf.h in the zlib library for more information.
  3276. .SS Configuring for Medium Model
  3277. Libpng's support for medium model has been tested on most of the popular
  3278. compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
  3279. defined, and FAR gets defined to far in pngconf.h, and you should be
  3280. all set. Everything in the library (except for zlib's structure) is
  3281. expecting far data. You must use the typedefs with the p or pp on
  3282. the end for pointers (or at least look at them and be careful). Make
  3283. note that the rows of data are defined as png_bytepp, which is
  3284. an "unsigned char far * far *".
  3285. .SS Configuring for gui/windowing platforms:
  3286. You will need to write new error and warning functions that use the GUI
  3287. interface, as described previously, and set them to be the error and
  3288. warning functions at the time that png_create_*_struct() is called,
  3289. in order to have them available during the structure initialization.
  3290. They can be changed later via png_set_error_fn(). On some compilers,
  3291. you may also have to change the memory allocators (png_malloc, etc.).
  3292. .SS Configuring for compiler xxx:
  3293. All includes for libpng are in pngconf.h. If you need to add, change
  3294. or delete an include, this is the place to do it.
  3295. The includes that are not needed outside libpng are placed in pngpriv.h,
  3296. which is only used by the routines inside libpng itself.
  3297. The files in libpng proper only include pngpriv.h and png.h, which
  3298. %14%in turn includes pngconf.h.
  3299. in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h.
  3300. As of libpng-1.5.0, pngpriv.h also includes three other private header
  3301. files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material
  3302. that previously appeared in the public headers.
  3303. .SS Configuring zlib:
  3304. There are special functions to configure the compression. Perhaps the
  3305. most useful one changes the compression level, which currently uses
  3306. input compression values in the range 0 - 9. The library normally
  3307. uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
  3308. have shown that for a large majority of images, compression values in
  3309. the range 3-6 compress nearly as well as higher levels, and do so much
  3310. faster. For online applications it may be desirable to have maximum speed
  3311. (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
  3312. specify no compression (Z_NO_COMPRESSION = 0), but this would create
  3313. files larger than just storing the raw bitmap. You can specify the
  3314. compression level by calling:
  3315. #include zlib.h
  3316. png_set_compression_level(png_ptr, level);
  3317. Another useful one is to reduce the memory level used by the library.
  3318. The memory level defaults to 8, but it can be lowered if you are
  3319. short on memory (running DOS, for example, where you only have 640K).
  3320. Note that the memory level does have an effect on compression; among
  3321. other things, lower levels will result in sections of incompressible
  3322. data being emitted in smaller stored blocks, with a correspondingly
  3323. larger relative overhead of up to 15% in the worst case.
  3324. #include zlib.h
  3325. png_set_compression_mem_level(png_ptr, level);
  3326. The other functions are for configuring zlib. They are not recommended
  3327. for normal use and may result in writing an invalid PNG file. See
  3328. zlib.h for more information on what these mean.
  3329. #include zlib.h
  3330. png_set_compression_strategy(png_ptr,
  3331. strategy);
  3332. png_set_compression_window_bits(png_ptr,
  3333. window_bits);
  3334. png_set_compression_method(png_ptr, method);
  3335. png_set_compression_buffer_size(png_ptr, size);
  3336. As of libpng version 1.5.4, additional APIs became
  3337. available to set these separately for non-IDAT
  3338. compressed chunks such as zTXt, iTXt, and iCCP:
  3339. #include zlib.h
  3340. #if PNG_LIBPNG_VER <= 10504
  3341. png_set_text_compression_level(png_ptr, level);
  3342. png_set_text_compression_mem_level(png_ptr, level);
  3343. png_set_text_compression_strategy(png_ptr,
  3344. strategy);
  3345. png_set_text_compression_window_bits(png_ptr,
  3346. window_bits);
  3347. png_set_text_compression_method(png_ptr, method);
  3348. #endif
  3349. .SS Controlling row filtering
  3350. If you want to control whether libpng uses filtering or not, which
  3351. filters are used, and how it goes about picking row filters, you
  3352. can call one of these functions. The selection and configuration
  3353. of row filters can have a significant impact on the size and
  3354. encoding speed and a somewhat lesser impact on the decoding speed
  3355. of an image. Filtering is enabled by default for RGB and grayscale
  3356. images (with and without alpha), but not for paletted images nor
  3357. for any images with bit depths less than 8 bits/pixel.
  3358. The 'method' parameter sets the main filtering method, which is
  3359. currently only '0' in the PNG 1.2 specification. The 'filters'
  3360. parameter sets which filter(s), if any, should be used for each
  3361. scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
  3362. to turn filtering on and off, respectively.
  3363. Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
  3364. PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
  3365. ORed together with '|' to specify one or more filters to use.
  3366. These filters are described in more detail in the PNG specification.
  3367. If you intend to change the filter type during the course of writing
  3368. the image, you should start with flags set for all of the filters
  3369. you intend to use so that libpng can initialize its internal
  3370. structures appropriately for all of the filter types. (Note that this
  3371. means the first row must always be adaptively filtered, because libpng
  3372. currently does not allocate the filter buffers until png_write_row()
  3373. is called for the first time.)
  3374. filters = PNG_FILTER_NONE | PNG_FILTER_SUB
  3375. PNG_FILTER_UP | PNG_FILTER_AVG |
  3376. PNG_FILTER_PAETH | PNG_ALL_FILTERS;
  3377. png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
  3378. filters);
  3379. The second parameter can also be
  3380. PNG_INTRAPIXEL_DIFFERENCING if you are
  3381. writing a PNG to be embedded in a MNG
  3382. datastream. This parameter must be the
  3383. same as the value of filter_method used
  3384. in png_set_IHDR().
  3385. It is also possible to influence how libpng chooses from among the
  3386. available filters. This is done in one or both of two ways - by
  3387. telling it how important it is to keep the same filter for successive
  3388. rows, and by telling it the relative computational costs of the filters.
  3389. double weights[3] = {1.5, 1.3, 1.1},
  3390. costs[PNG_FILTER_VALUE_LAST] =
  3391. {1.0, 1.3, 1.3, 1.5, 1.7};
  3392. png_set_filter_heuristics(png_ptr,
  3393. PNG_FILTER_HEURISTIC_WEIGHTED, 3,
  3394. weights, costs);
  3395. The weights are multiplying factors that indicate to libpng that the
  3396. row filter should be the same for successive rows unless another row filter
  3397. is that many times better than the previous filter. In the above example,
  3398. if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
  3399. "sum of absolute differences" 1.5 x 1.3 times higher than other filters
  3400. and still be chosen, while the NONE filter could have a sum 1.1 times
  3401. higher than other filters and still be chosen. Unspecified weights are
  3402. taken to be 1.0, and the specified weights should probably be declining
  3403. like those above in order to emphasize recent filters over older filters.
  3404. The filter costs specify for each filter type a relative decoding cost
  3405. to be considered when selecting row filters. This means that filters
  3406. with higher costs are less likely to be chosen over filters with lower
  3407. costs, unless their "sum of absolute differences" is that much smaller.
  3408. The costs do not necessarily reflect the exact computational speeds of
  3409. the various filters, since this would unduly influence the final image
  3410. size.
  3411. Note that the numbers above were invented purely for this example and
  3412. are given only to help explain the function usage. Little testing has
  3413. been done to find optimum values for either the costs or the weights.
  3414. .SS Removing unwanted object code
  3415. There are a bunch of #define's in pngconf.h that control what parts of
  3416. libpng are compiled. All the defines end in _SUPPORTED. If you are
  3417. never going to use a capability, you can change the #define to #undef
  3418. before recompiling libpng and save yourself code and data space, or
  3419. you can turn off individual capabilities with defines that begin with
  3420. PNG_NO_.
  3421. In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
  3422. You can also turn all of the transforms and ancillary chunk capabilities
  3423. off en masse with compiler directives that define
  3424. PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
  3425. or all four,
  3426. along with directives to turn on any of the capabilities that you do
  3427. want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
  3428. transformations but still leave the library fully capable of reading
  3429. and writing PNG files with all known public chunks. Use of the
  3430. PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
  3431. that is incapable of reading or writing ancillary chunks. If you are
  3432. not using the progressive reading capability, you can turn that off
  3433. with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
  3434. capability, which you'll still have).
  3435. All the reading and writing specific code are in separate files, so the
  3436. linker should only grab the files it needs. However, if you want to
  3437. make sure, or if you are building a stand alone library, all the
  3438. reading files start with "pngr" and all the writing files start with "pngw".
  3439. The files that don't match either (like png.c, pngtrans.c, etc.)
  3440. are used for both reading and writing, and always need to be included.
  3441. The progressive reader is in pngpread.c
  3442. If you are creating or distributing a dynamically linked library (a .so
  3443. or DLL file), you should not remove or disable any parts of the library,
  3444. as this will cause applications linked with different versions of the
  3445. library to fail if they call functions not available in your library.
  3446. The size of the library itself should not be an issue, because only
  3447. those sections that are actually used will be loaded into memory.
  3448. .SS Requesting debug printout
  3449. The macro definition PNG_DEBUG can be used to request debugging
  3450. printout. Set it to an integer value in the range 0 to 3. Higher
  3451. numbers result in increasing amounts of debugging information. The
  3452. information is printed to the "stderr" file, unless another file
  3453. name is specified in the PNG_DEBUG_FILE macro definition.
  3454. When PNG_DEBUG > 0, the following functions (macros) become available:
  3455. png_debug(level, message)
  3456. png_debug1(level, message, p1)
  3457. png_debug2(level, message, p1, p2)
  3458. in which "level" is compared to PNG_DEBUG to decide whether to print
  3459. the message, "message" is the formatted string to be printed,
  3460. and p1 and p2 are parameters that are to be embedded in the string
  3461. according to printf-style formatting directives. For example,
  3462. png_debug1(2, "foo=%d\n", foo);
  3463. is expanded to
  3464. if (PNG_DEBUG > 2)
  3465. fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
  3466. When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
  3467. can still use PNG_DEBUG to control your own debugging:
  3468. #ifdef PNG_DEBUG
  3469. fprintf(stderr, ...
  3470. #endif
  3471. When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
  3472. having level = 0 will be printed. There aren't any such statements in
  3473. this version of libpng, but if you insert some they will be printed.
  3474. .SH VI. MNG support
  3475. The MNG specification (available at http://www.libpng.org/pub/mng) allows
  3476. certain extensions to PNG for PNG images that are embedded in MNG datastreams.
  3477. Libpng can support some of these extensions. To enable them, use the
  3478. png_permit_mng_features() function:
  3479. feature_set = png_permit_mng_features(png_ptr, mask)
  3480. mask is a png_uint_32 containing the bitwise OR of the
  3481. features you want to enable. These include
  3482. PNG_FLAG_MNG_EMPTY_PLTE
  3483. PNG_FLAG_MNG_FILTER_64
  3484. PNG_ALL_MNG_FEATURES
  3485. feature_set is a png_uint_32 that is the bitwise AND of
  3486. your mask with the set of MNG features that is
  3487. supported by the version of libpng that you are using.
  3488. It is an error to use this function when reading or writing a standalone
  3489. PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
  3490. in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
  3491. and the MHDR and MEND chunks. Libpng does not provide support for these
  3492. or any other MNG chunks; your application must provide its own support for
  3493. them. You may wish to consider using libmng (available at
  3494. http://www.libmng.com) instead.
  3495. .SH VII. Changes to Libpng from version 0.88
  3496. It should be noted that versions of libpng later than 0.96 are not
  3497. distributed by the original libpng author, Guy Schalnat, nor by
  3498. Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
  3499. distributed versions 0.89 through 0.96, but rather by another member
  3500. of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
  3501. still alive and well, but they have moved on to other things.
  3502. The old libpng functions png_read_init(), png_write_init(),
  3503. png_info_init(), png_read_destroy(), and png_write_destroy() have been
  3504. moved to PNG_INTERNAL in version 0.95 to discourage their use. These
  3505. functions will be removed from libpng version 1.4.0.
  3506. The preferred method of creating and initializing the libpng structures is
  3507. via the png_create_read_struct(), png_create_write_struct(), and
  3508. png_create_info_struct() because they isolate the size of the structures
  3509. from the application, allow version error checking, and also allow the
  3510. use of custom error handling routines during the initialization, which
  3511. the old functions do not. The functions png_read_destroy() and
  3512. png_write_destroy() do not actually free the memory that libpng
  3513. allocated for these structs, but just reset the data structures, so they
  3514. can be used instead of png_destroy_read_struct() and
  3515. png_destroy_write_struct() if you feel there is too much system overhead
  3516. allocating and freeing the png_struct for each image read.
  3517. Setting the error callbacks via png_set_message_fn() before
  3518. png_read_init() as was suggested in libpng-0.88 is no longer supported
  3519. because this caused applications that do not use custom error functions
  3520. to fail if the png_ptr was not initialized to zero. It is still possible
  3521. to set the error callbacks AFTER png_read_init(), or to change them with
  3522. png_set_error_fn(), which is essentially the same function, but with a new
  3523. name to force compilation errors with applications that try to use the old
  3524. method.
  3525. Starting with version 1.0.7, you can find out which version of the library
  3526. you are using at run-time:
  3527. png_uint_32 libpng_vn = png_access_version_number();
  3528. The number libpng_vn is constructed from the major version, minor
  3529. version with leading zero, and release number with leading zero,
  3530. (e.g., libpng_vn for version 1.0.7 is 10007).
  3531. Note that this function does not take a png_ptr, so you can call it
  3532. before you've created one.
  3533. You can also check which version of png.h you used when compiling your
  3534. application:
  3535. png_uint_32 application_vn = PNG_LIBPNG_VER;
  3536. .SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
  3537. Support for user memory management was enabled by default. To
  3538. accomplish this, the functions png_create_read_struct_2(),
  3539. png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
  3540. png_malloc_default(), and png_free_default() were added.
  3541. Support for the iTXt chunk has been enabled by default as of
  3542. version 1.2.41.
  3543. Support for certain MNG features was enabled.
  3544. Support for numbered error messages was added. However, we never got
  3545. around to actually numbering the error messages. The function
  3546. png_set_strip_error_numbers() was added (Note: the prototype for this
  3547. function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
  3548. builds of libpng-1.2.15. It was restored in libpng-1.2.36).
  3549. The png_malloc_warn() function was added at libpng-1.2.3. This issues
  3550. a png_warning and returns NULL instead of aborting when it fails to
  3551. acquire the requested memory allocation.
  3552. Support for setting user limits on image width and height was enabled
  3553. by default. The functions png_set_user_limits(), png_get_user_width_max(),
  3554. and png_get_user_height_max() were added at libpng-1.2.6.
  3555. The png_set_add_alpha() function was added at libpng-1.2.7.
  3556. The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
  3557. Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
  3558. tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
  3559. deprecated.
  3560. A number of macro definitions in support of runtime selection of
  3561. assembler code features (especially Intel MMX code support) were
  3562. added at libpng-1.2.0:
  3563. PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
  3564. PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
  3565. PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
  3566. PNG_ASM_FLAG_MMX_READ_INTERLACE
  3567. PNG_ASM_FLAG_MMX_READ_FILTER_SUB
  3568. PNG_ASM_FLAG_MMX_READ_FILTER_UP
  3569. PNG_ASM_FLAG_MMX_READ_FILTER_AVG
  3570. PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
  3571. PNG_ASM_FLAGS_INITIALIZED
  3572. PNG_MMX_READ_FLAGS
  3573. PNG_MMX_FLAGS
  3574. PNG_MMX_WRITE_FLAGS
  3575. PNG_MMX_FLAGS
  3576. We added the following functions in support of runtime
  3577. selection of assembler code features:
  3578. png_get_mmx_flagmask()
  3579. png_set_mmx_thresholds()
  3580. png_get_asm_flags()
  3581. png_get_mmx_bitdepth_threshold()
  3582. png_get_mmx_rowbytes_threshold()
  3583. png_set_asm_flags()
  3584. We replaced all of these functions with simple stubs in libpng-1.2.20,
  3585. when the Intel assembler code was removed due to a licensing issue.
  3586. These macros are deprecated:
  3587. PNG_READ_TRANSFORMS_NOT_SUPPORTED
  3588. PNG_PROGRESSIVE_READ_NOT_SUPPORTED
  3589. PNG_NO_SEQUENTIAL_READ_SUPPORTED
  3590. PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
  3591. PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
  3592. PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
  3593. They have been replaced, respectively, by:
  3594. PNG_NO_READ_TRANSFORMS
  3595. PNG_NO_PROGRESSIVE_READ
  3596. PNG_NO_SEQUENTIAL_READ
  3597. PNG_NO_WRITE_TRANSFORMS
  3598. PNG_NO_READ_ANCILLARY_CHUNKS
  3599. PNG_NO_WRITE_ANCILLARY_CHUNKS
  3600. PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
  3601. deprecated since libpng-1.0.16 and libpng-1.2.6.
  3602. The function
  3603. png_check_sig(sig, num)
  3604. was replaced with
  3605. !png_sig_cmp(sig, 0, num)
  3606. It has been deprecated since libpng-0.90.
  3607. The function
  3608. png_set_gray_1_2_4_to_8()
  3609. which also expands tRNS to alpha was replaced with
  3610. png_set_expand_gray_1_2_4_to_8()
  3611. which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
  3612. .SH IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
  3613. Private libpng prototypes and macro definitions were moved from
  3614. png.h and pngconf.h into a new pngpriv.h header file.
  3615. Functions png_set_benign_errors(), png_benign_error(), and
  3616. png_chunk_benign_error() were added.
  3617. Support for setting the maximum amount of memory that the application
  3618. will allocate for reading chunks was added, as a security measure.
  3619. The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
  3620. were added to the library.
  3621. We implemented support for I/O states by adding png_ptr member io_state
  3622. and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
  3623. We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
  3624. input transforms.
  3625. Checking for and reporting of errors in the IHDR chunk is more thorough.
  3626. Support for global arrays was removed, to improve thread safety.
  3627. Some obsolete/deprecated macros and functions have been removed.
  3628. Typecasted NULL definitions such as
  3629. #define png_voidp_NULL (png_voidp)NULL
  3630. were eliminated. If you used these in your application, just use
  3631. NULL instead.
  3632. The png_struct and info_struct members "trans" and "trans_values" were
  3633. changed to "trans_alpha" and "trans_color", respectively.
  3634. The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
  3635. were removed.
  3636. The PNG_1_0_X and PNG_1_2_X macros were eliminated.
  3637. The PNG_LEGACY_SUPPORTED macro was eliminated.
  3638. Many WIN32_WCE #ifdefs were removed.
  3639. The functions png_read_init(info_ptr), png_write_init(info_ptr),
  3640. png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
  3641. have been removed. They have been deprecated since libpng-0.95.
  3642. The png_permit_empty_plte() was removed. It has been deprecated
  3643. since libpng-1.0.9. Use png_permit_mng_features() instead.
  3644. We removed the obsolete stub functions png_get_mmx_flagmask(),
  3645. png_set_mmx_thresholds(), png_get_asm_flags(),
  3646. png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
  3647. png_set_asm_flags(), and png_mmx_supported()
  3648. We removed the obsolete png_check_sig(), png_memcpy_check(), and
  3649. png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),
  3650. and memset(), respectively.
  3651. The function png_set_gray_1_2_4_to_8() was removed. It has been
  3652. deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
  3653. png_set_expand_gray_1_2_4_to_8() because the former function also
  3654. expanded any tRNS chunk to an alpha channel.
  3655. Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
  3656. were added and are used by default instead of the corresponding
  3657. functions. Unfortunately,
  3658. from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
  3659. function) incorrectly returned a value of type png_uint_32.
  3660. We changed the prototype for png_malloc() from
  3661. png_malloc(png_structp png_ptr, png_uint_32 size)
  3662. to
  3663. png_malloc(png_structp png_ptr, png_alloc_size_t size)
  3664. This also applies to the prototype for the user replacement malloc_fn().
  3665. The png_calloc() function was added and is used in place of
  3666. of "png_malloc(); memset();" except in the case in png_read_png()
  3667. where the array consists of pointers; in this case a "for" loop is used
  3668. after the png_malloc() to set the pointers to NULL, to give robust.
  3669. behavior in case the application runs out of memory part-way through
  3670. the process.
  3671. We changed the prototypes of png_get_compression_buffer_size() and
  3672. png_set_compression_buffer_size() to work with png_size_t instead of
  3673. png_uint_32.
  3674. Support for numbered error messages was removed by default, since we
  3675. never got around to actually numbering the error messages. The function
  3676. png_set_strip_error_numbers() was removed from the library by default.
  3677. The png_zalloc() and png_zfree() functions are no longer exported.
  3678. The png_zalloc() function no longer zeroes out the memory that it
  3679. allocates.
  3680. Support for dithering was disabled by default in libpng-1.4.0, because
  3681. it has not been well tested and doesn't actually "dither".
  3682. The code was not
  3683. removed, however, and could be enabled by building libpng with
  3684. PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
  3685. was reenabled, but the function was renamed png_set_quantize() to
  3686. reflect more accurately what it actually does. At the same time,
  3687. the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
  3688. PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
  3689. was renamed to PNG_READ_QUANTIZE_SUPPORTED.
  3690. We removed the trailing '.' from the warning and error messages.
  3691. .SH X. Changes to Libpng from version 1.4.x to 1.5.x
  3692. From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
  3693. function) incorrectly returned a value of type png_uint_32.
  3694. A. Changes that affect users of libpng
  3695. There are no substantial API changes between the non-deprecated parts of
  3696. the 1.4.5 API and the 1.5.0 API, however the ability to directly access
  3697. the main libpng control structures, png_struct and png_info, deprecated
  3698. in earlier versions of libpng, has been completely removed from
  3699. libpng 1.5.
  3700. We no longer include zlib.h in png.h. Applications that need access
  3701. to information in zlib.h will need to add the '#include "zlib.h"'
  3702. directive. It does not matter whether it is placed prior to or after
  3703. the '"#include png.h"' directive.
  3704. We moved the png_strcpy(), png_strncpy(), png_strlen(), png_memcpy(),
  3705. png_memcmp(), png_sprintf, and png_memcpy() macros into a private
  3706. header file (pngpriv.h) that is not accessible to applications.
  3707. In png_get_iCCP, the type of "profile" was changed from png_charpp
  3708. to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
  3709. There are changes of form in png.h, including new and changed macros to
  3710. declare parts of the API. Some API functions with arguments that are
  3711. pointers to data not modified within the function have been corrected to
  3712. declare these arguments with PNG_CONST.
  3713. Much of the internal use of C macros to control the library build has also
  3714. changed and some of this is visible in the exported header files, in
  3715. particular the use of macros to control data and API elements visible
  3716. during application compilation may require significant revision to
  3717. application code. (It is extremely rare for an application to do this.)
  3718. Any program that compiled against libpng 1.4 and did not use deprecated
  3719. features or access internal library structures should compile and work
  3720. against libpng 1.5, except for the change in the prototype for
  3721. png_get_iCCP() and png_set_iCCP() API functions mentioned above.
  3722. libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
  3723. interlaced images. The macros return the number of rows and columns in
  3724. each pass and information that can be used to de-interlace and (if
  3725. absolutely necessary) interlace an image.
  3726. libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
  3727. the application-provided png_longjmp_ptr on the internal, but application
  3728. initialized, longjmp buffer. It is provided as a convenience to avoid
  3729. the need to use the png_jmpbuf macro, which had the unnecessary side
  3730. effect of resetting the internal png_longjmp_ptr value.
  3731. libpng 1.5.0 includes a complete fixed point API. By default this is
  3732. present along with the corresponding floating point API. In general the
  3733. fixed point API is faster and smaller than the floating point one because
  3734. the PNG file format used fixed point, not floating point. This applies
  3735. even if the library uses floating point in internal calculations. A new
  3736. macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
  3737. uses floating point arithmetic (the default) or fixed point arithmetic
  3738. internally for performance critical calculations such as gamma correction.
  3739. In some cases, the gamma calculations may produce slightly different
  3740. results. This has changed the results in png_rgb_to_gray and in alpha
  3741. composition (png_set_background for example). This applies even if the
  3742. original image was already linear (gamma == 1.0) and, therefore, it is
  3743. not necessary to linearize the image. This is because libpng has *not*
  3744. been changed to optimize that case correctly, yet.
  3745. Fixed point support for the sCAL chunk comes with an important caveat;
  3746. the sCAL specification uses a decimal encoding of floating point values
  3747. and the accuracy of PNG fixed point values is insufficient for
  3748. representation of these values. Consequently a "string" API
  3749. (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
  3750. arbitrary sCAL chunks in the absence of either the floating point API or
  3751. internal floating point calculations.
  3752. Applications no longer need to include the optional distribution header
  3753. file pngusr.h or define the corresponding macros during application
  3754. build in order to see the correct variant of the libpng API. From 1.5.0
  3755. application code can check for the corresponding _SUPPORTED macro:
  3756. #ifdef PNG_INCH_CONVERSIONS_SUPPORTED
  3757. /* code that uses the inch conversion APIs. */
  3758. #endif
  3759. This macro will only be defined if the inch conversion functions have been
  3760. compiled into libpng. The full set of macros, and whether or not support
  3761. has been compiled in, are available in the header file pnglibconf.h.
  3762. This header file is specific to the libpng build. Notice that prior to
  3763. 1.5.0 the _SUPPORTED macros would always have the default definition unless
  3764. reset by pngusr.h or by explicit settings on the compiler command line.
  3765. These settings may produce compiler warnings or errors in 1.5.0 because
  3766. of macro redefinition.
  3767. From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
  3768. function) incorrectly returned a value of type png_uint_32. libpng 1.5.0
  3769. is consistent with the implementation in 1.4.5 and 1.2.x (where the macro
  3770. did not exist.)
  3771. Applications can now choose whether to use these macros or to call the
  3772. corresponding function by defining PNG_USE_READ_MACROS or
  3773. PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
  3774. only supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0
  3775. will lead to a link failure.
  3776. Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
  3777. when compressing the IDAT data and textual data such as zTXt and iCCP.
  3778. In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
  3779. We added five png_set_text_*() functions for setting the parameters to
  3780. use with textual data.
  3781. Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
  3782. option was off by default, and slightly inaccurate scaling occurred.
  3783. This option can no longer be turned off, and the choice of accurate
  3784. or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
  3785. API for accurate scaling or the old png_set_strip_16_to_8() API for simple
  3786. chopping.
  3787. Prior to libpng-1.5.4, the png_set_user_limits() function could only be
  3788. used to reduce the width and height limits from the value of
  3789. PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
  3790. that it could be used to override them. Now this function will reduce or
  3791. increase the limits.
  3792. B. Changes to the build and configuration of libpng
  3793. Details of internal changes to the library code can be found in the CHANGES
  3794. file and in the GIT repository logs. These will be of no concern to the vast
  3795. majority of library users or builders, however the few who configure libpng
  3796. to a non-default feature set may need to change how this is done.
  3797. There should be no need for library builders to alter build scripts if
  3798. these use the distributed build support - configure or the makefiles -
  3799. however users of the makefiles may care to update their build scripts
  3800. to build pnglibconf.h where the corresponding makefile does not do so.
  3801. Building libpng with a non-default configuration has changed completely.
  3802. The old method using pngusr.h should still work correctly even though the
  3803. way pngusr.h is used in the build has been changed; however, library
  3804. builders will probably want to examine the changes to take advantage of
  3805. new capabilities and to simplify their build system.
  3806. B.1 Specific changes to library configuration capabilities
  3807. The library now supports a complete fixed point implementation and can
  3808. thus be used on systems that have no floating point support or very
  3809. limited or slow support. Previously gamma correction, an essential part
  3810. of complete PNG support, required reasonably fast floating point.
  3811. As part of this the choice of internal implementation has been made
  3812. independent of the choice of fixed versus floating point APIs and all the
  3813. missing fixed point APIs have been implemented.
  3814. The exact mechanism used to control attributes of API functions has
  3815. changed. A single set of operating system independent macro definitions
  3816. is used and operating system specific directives are defined in
  3817. pnglibconf.h
  3818. As part of this the mechanism used to choose procedure call standards on
  3819. those systems that allow a choice has been changed. At present this only
  3820. affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems
  3821. running on Intel processors. As before, PNGAPI is defined where required
  3822. to control the exported API functions; however, two new macros, PNGCBAPI
  3823. and PNGCAPI, are used instead for callback functions (PNGCBAPI) and
  3824. (PNGCAPI) for functions that must match a C library prototype (currently
  3825. only png_longjmp_ptr, which must match the C longjmp function.) The new
  3826. approach is documented in pngconf.h
  3827. Despite these changes, libpng 1.5.0 only supports the native C function
  3828. calling standard on those platforms tested so far (__cdecl on Microsoft
  3829. Windows). This is because the support requirements for alternative
  3830. calling conventions seem to no longer exist. Developers who find it
  3831. necessary to set PNG_API_RULE to 1 should advise the mailing list
  3832. (png-mng-implement) of this and library builders who use Openwatcom and
  3833. therefore set PNG_API_RULE to 2 should also contact the mailing list.
  3834. A new test program, pngvalid, is provided in addition to pngtest.
  3835. pngvalid validates the arithmetic accuracy of the gamma correction
  3836. calculations and includes a number of validations of the file format.
  3837. A subset of the full range of tests is run when "make check" is done
  3838. (in the 'configure' build.) pngvalid also allows total allocated memory
  3839. usage to be evaluated and performs additional memory overwrite validation.
  3840. Many changes to individual feature macros have been made. The following
  3841. are the changes most likely to be noticed by library builders who
  3842. configure libpng:
  3843. 1) All feature macros now have consistent naming:
  3844. #define PNG_NO_feature turns the feature off
  3845. #define PNG_feature_SUPPORTED turns the feature on
  3846. pnglibconf.h contains one line for each feature macro which is either:
  3847. #define PNG_feature_SUPPORTED
  3848. if the feature is supported or:
  3849. /*#undef PNG_feature_SUPPORTED*/
  3850. if it is not. Library code consistently checks for the 'SUPPORTED' macro.
  3851. It does not, and libpng applications should not, check for the 'NO' macro
  3852. which will not normally be defined even if the feature is not supported.
  3853. The 'NO' macros are only used internally for setting or not setting the
  3854. corresponding 'SUPPORTED' macros.
  3855. Compatibility with the old names is provided as follows:
  3856. PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
  3857. And the following definitions disable the corresponding feature:
  3858. PNG_SETJMP_NOT_SUPPORTED disables SETJMP
  3859. PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
  3860. PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
  3861. PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
  3862. PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
  3863. PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
  3864. Library builders should remove use of the above, inconsistent, names.
  3865. 2) Warning and error message formatting was previously conditional on
  3866. the STDIO feature. The library has been changed to use the
  3867. CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
  3868. the library no longer uses the printf(3) functions, even though the
  3869. default read/write implementations use (FILE) style stdio.h functions.
  3870. 3) Three feature macros now control the fixed/floating point decisions:
  3871. PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
  3872. PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
  3873. practice these are normally required internally anyway (because the PNG
  3874. file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
  3875. merely stops the function from being exported.
  3876. PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
  3877. point implementation or the fixed point one. Typically the fixed point
  3878. implementation is larger and slower than the floating point implementation
  3879. on a system that supports floating point, however it may be faster on a
  3880. system which lacks floating point hardware and therefore uses a software
  3881. emulation.
  3882. 4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
  3883. functions to read and write ints to be disabled independently of
  3884. PNG_USE_READ_MACROS, which allows libpng to be built with the functions
  3885. even though the default is to use the macros - this allows applications
  3886. to choose at app buildtime whether or not to use macros (previously
  3887. impossible because the functions weren't in the default build.)
  3888. B.2 Changes to the configuration mechanism
  3889. Prior to libpng-1.5.0 library builders who needed to configure libpng
  3890. had either to modify the exported pngconf.h header file to add system
  3891. specific configuration or had to write feature selection macros into
  3892. pngusr.h and cause this to be included into pngconf.h by defining
  3893. PNG_USER_CONFIG. The latter mechanism had the disadvantage that an
  3894. application built without PNG_USER_CONFIG defined would see the
  3895. unmodified, default, libpng API and thus would probably fail to link.
  3896. These mechanisms still work in the configure build and in any makefile
  3897. build that builds pnglibconf.h, although the feature selection macros
  3898. have changed somewhat as described above. In 1.5.0, however, pngusr.h is
  3899. processed only once, when the exported header file pnglibconf.h is built.
  3900. pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the
  3901. build of pnglibconf.h and it is never included in an application build.
  3902. The rarely used alternative of adding a list of feature macros to the
  3903. CFLAGS setting in the build also still works, however the macros will be
  3904. copied to pnglibconf.h and this may produce macro redefinition warnings
  3905. when the individual C files are compiled.
  3906. All configuration now only works if pnglibconf.h is built from
  3907. scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan
  3908. (the original author of awk) maintains C source code of that awk and this
  3909. and all known later implementations (often called by subtly different
  3910. names - nawk and gawk for example) are adequate to build pnglibconf.h.
  3911. The Sun Microsystems (now Oracle) program 'awk' is an earlier version
  3912. and does not work; this may also apply to other systems that have a
  3913. functioning awk called 'nawk'.
  3914. Configuration options are now documented in scripts/pnglibconf.dfa. This
  3915. file also includes dependency information that ensures a configuration is
  3916. consistent; that is, if a feature is switched off dependent features are
  3917. also removed. As a recommended alternative to using feature macros in
  3918. pngusr.h a system builder may also define equivalent options in pngusr.dfa
  3919. (or, indeed, any file) and add that to the configuration by setting
  3920. DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate
  3921. how to do this, and a case where pngusr.h is still required.
  3922. .SH XI. Detecting libpng
  3923. The png_get_io_ptr() function has been present since libpng-0.88, has never
  3924. changed, and is unaffected by conditional compilation macros. It is the
  3925. best choice for use in configure scripts for detecting the presence of any
  3926. libpng version since 0.88. In an autoconf "configure.in" you could use
  3927. AC_CHECK_LIB(png, png_get_io_ptr, ...
  3928. .SH XII. Source code repository
  3929. Since about February 2009, version 1.2.34, libpng has been under "git" source
  3930. control. The git repository was built from old libpng-x.y.z.tar.gz files
  3931. going back to version 0.70. You can access the git repository (read only)
  3932. at
  3933. git://libpng.git.sourceforge.net/gitroot/libpng
  3934. or you can browse it via "gitweb" at
  3935. http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
  3936. Patches can be sent to glennrp at users.sourceforge.net or to
  3937. png-mng-implement at lists.sourceforge.net or you can upload them to
  3938. the libpng bug tracker at
  3939. http://libpng.sourceforge.net
  3940. We also accept patches built from the tar or zip distributions, and
  3941. simple verbal discriptions of bug fixes, reported either to the
  3942. SourceForge bug tracker, to the png-mng-implement at lists.sf.net
  3943. mailing list, or directly to glennrp.
  3944. .SH XIII. Coding style
  3945. Our coding style is similar to the "Allman" style, with curly
  3946. braces on separate lines:
  3947. if (condition)
  3948. {
  3949. action;
  3950. }
  3951. else if (another condition)
  3952. {
  3953. another action;
  3954. }
  3955. The braces can be omitted from simple one-line actions:
  3956. if (condition)
  3957. return (0);
  3958. We use 3-space indentation, except for continued statements which
  3959. are usually indented the same as the first line of the statement
  3960. plus four more spaces.
  3961. For macro definitions we use 2-space indentation, always leaving the "#"
  3962. in the first column.
  3963. #ifndef PNG_NO_FEATURE
  3964. # ifndef PNG_FEATURE_SUPPORTED
  3965. # define PNG_FEATURE_SUPPORTED
  3966. # endif
  3967. #endif
  3968. Comments appear with the leading "/*" at the same indentation as
  3969. the statement that follows the comment:
  3970. /* Single-line comment */
  3971. statement;
  3972. /* This is a multiple-line
  3973. * comment.
  3974. */
  3975. statement;
  3976. Very short comments can be placed after the end of the statement
  3977. to which they pertain:
  3978. statement; /* comment */
  3979. We don't use C++ style ("//") comments. We have, however,
  3980. used them in the past in some now-abandoned MMX assembler
  3981. code.
  3982. Functions and their curly braces are not indented, and
  3983. exported functions are marked with PNGAPI:
  3984. /* This is a public function that is visible to
  3985. * application programmers. It does thus-and-so.
  3986. */
  3987. void PNGAPI
  3988. png_exported_function(png_ptr, png_info, foo)
  3989. {
  3990. body;
  3991. }
  3992. The prototypes for all exported functions appear in png.h,
  3993. above the comment that says
  3994. /* Maintainer: Put new public prototypes here ... */
  3995. We mark all non-exported functions with "/* PRIVATE */"":
  3996. void /* PRIVATE */
  3997. png_non_exported_function(png_ptr, png_info, foo)
  3998. {
  3999. body;
  4000. }
  4001. The prototypes for non-exported functions (except for those in
  4002. pngtest) appear in
  4003. pngpriv.h
  4004. above the comment that says
  4005. /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */
  4006. To avoid polluting the global namespace, the names of all exported
  4007. functions and variables begin with "png_", and all publicly visible C
  4008. preprocessor macros begin with "PNG_". We request that applications that
  4009. use libpng *not* begin any of their own symbols with either of these strings.
  4010. We put a space after each comma and after each semicolon
  4011. in "for" statements, and we put spaces before and after each
  4012. C binary operator and after "for" or "while", and before
  4013. "?". We don't put a space between a typecast and the expression
  4014. being cast, nor do we put one between a function name and the
  4015. left parenthesis that follows it:
  4016. for (i = 2; i > 0; --i)
  4017. y[i] = a(x) + (int)b;
  4018. We prefer #ifdef and #ifndef to #if defined() and if !defined()
  4019. when there is only one macro being tested.
  4020. We prefer to express integers that are used as bit masks in hex format,
  4021. with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100).
  4022. We do not use the TAB character for indentation in the C sources.
  4023. Lines do not exceed 80 characters.
  4024. Other rules can be inferred by inspecting the libpng source.
  4025. .SH XIV. Y2K Compliance in libpng
  4026. February 18, 2012
  4027. Since the PNG Development group is an ad-hoc body, we can't make
  4028. an official declaration.
  4029. This is your unofficial assurance that libpng from version 0.71 and
  4030. upward through 1.5.9 are Y2K compliant. It is my belief that earlier
  4031. versions were also Y2K compliant.
  4032. Libpng only has three year fields. One is a 2-byte unsigned integer that
  4033. will hold years up to 65535. The other two hold the date in text
  4034. format, and will hold years up to 9999.
  4035. The integer is
  4036. "png_uint_16 year" in png_time_struct.
  4037. The strings are
  4038. "png_charp time_buffer" in png_struct and
  4039. "near_time_buffer", which is a local character string in png.c.
  4040. There are seven time-related functions:
  4041. png_convert_to_rfc_1123() in png.c
  4042. (formerly png_convert_to_rfc_1152() in error)
  4043. png_convert_from_struct_tm() in pngwrite.c, called
  4044. in pngwrite.c
  4045. png_convert_from_time_t() in pngwrite.c
  4046. png_get_tIME() in pngget.c
  4047. png_handle_tIME() in pngrutil.c, called in pngread.c
  4048. png_set_tIME() in pngset.c
  4049. png_write_tIME() in pngwutil.c, called in pngwrite.c
  4050. All appear to handle dates properly in a Y2K environment. The
  4051. png_convert_from_time_t() function calls gmtime() to convert from system
  4052. clock time, which returns (year - 1900), which we properly convert to
  4053. the full 4-digit year. There is a possibility that applications using
  4054. libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
  4055. function, or that they are incorrectly passing only a 2-digit year
  4056. instead of "year - 1900" into the png_convert_from_struct_tm() function,
  4057. but this is not under our control. The libpng documentation has always
  4058. stated that it works with 4-digit years, and the APIs have been
  4059. documented as such.
  4060. The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
  4061. integer to hold the year, and can hold years as large as 65535.
  4062. zlib, upon which libpng depends, is also Y2K compliant. It contains
  4063. no date-related code.
  4064. Glenn Randers-Pehrson
  4065. libpng maintainer
  4066. PNG Development Group
  4067. .SH NOTE
  4068. Note about libpng version numbers:
  4069. Due to various miscommunications, unforeseen code incompatibilities
  4070. and occasional factors outside the authors' control, version numbering
  4071. on the library has not always been consistent and straightforward.
  4072. The following table summarizes matters since version 0.89c, which was
  4073. the first widely used release:
  4074. source png.h png.h shared-lib
  4075. version string int version
  4076. ------- ------ ----- ----------
  4077. 0.89c ("beta 3") 0.89 89 1.0.89
  4078. 0.90 ("beta 4") 0.90 90 0.90
  4079. 0.95 ("beta 5") 0.95 95 0.95
  4080. 0.96 ("beta 6") 0.96 96 0.96
  4081. 0.97b ("beta 7") 1.00.97 97 1.0.1
  4082. 0.97c 0.97 97 2.0.97
  4083. 0.98 0.98 98 2.0.98
  4084. 0.99 0.99 98 2.0.99
  4085. 0.99a-m 0.99 99 2.0.99
  4086. 1.00 1.00 100 2.1.0
  4087. 1.0.0 1.0.0 100 2.1.0
  4088. 1.0.0 (from here on, the 100 2.1.0
  4089. 1.0.1 png.h string is 10001 2.1.0
  4090. 1.0.1a-e identical to the 10002 from here on, the
  4091. 1.0.2 source version) 10002 shared library is 2.V
  4092. 1.0.2a-b 10003 where V is the source
  4093. 1.0.1 10001 code version except as
  4094. 1.0.1a-e 10002 2.1.0.1a-e noted.
  4095. 1.0.2 10002 2.1.0.2
  4096. 1.0.2a-b 10003 2.1.0.2a-b
  4097. 1.0.3 10003 2.1.0.3
  4098. 1.0.3a-d 10004 2.1.0.3a-d
  4099. 1.0.4 10004 2.1.0.4
  4100. 1.0.4a-f 10005 2.1.0.4a-f
  4101. 1.0.5 (+ 2 patches) 10005 2.1.0.5
  4102. 1.0.5a-d 10006 2.1.0.5a-d
  4103. 1.0.5e-r 10100 2.1.0.5e-r
  4104. 1.0.5s-v 10006 2.1.0.5s-v
  4105. 1.0.6 (+ 3 patches) 10006 2.1.0.6
  4106. 1.0.6d-g 10007 2.1.0.6d-g
  4107. 1.0.6h 10007 10.6h
  4108. 1.0.6i 10007 10.6i
  4109. 1.0.6j 10007 2.1.0.6j
  4110. 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
  4111. 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
  4112. 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
  4113. 1.0.7 1 10007 2.1.0.7
  4114. 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
  4115. 1.0.8rc1 1 10008 2.1.0.8rc1
  4116. 1.0.8 1 10008 2.1.0.8
  4117. 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
  4118. 1.0.9rc1 1 10009 2.1.0.9rc1
  4119. 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
  4120. 1.0.9rc2 1 10009 2.1.0.9rc2
  4121. 1.0.9 1 10009 2.1.0.9
  4122. 1.0.10beta1 1 10010 2.1.0.10beta1
  4123. 1.0.10rc1 1 10010 2.1.0.10rc1
  4124. 1.0.10 1 10010 2.1.0.10
  4125. 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
  4126. 1.0.11rc1 1 10011 2.1.0.11rc1
  4127. 1.0.11 1 10011 2.1.0.11
  4128. 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
  4129. 1.0.12rc1 2 10012 2.1.0.12rc1
  4130. 1.0.12 2 10012 2.1.0.12
  4131. 1.1.0a-f - 10100 2.1.1.0a-f abandoned
  4132. 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
  4133. 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
  4134. 1.2.0rc1 3 10200 3.1.2.0rc1
  4135. 1.2.0 3 10200 3.1.2.0
  4136. 1.2.1beta-4 3 10201 3.1.2.1beta1-4
  4137. 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
  4138. 1.2.1 3 10201 3.1.2.1
  4139. 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
  4140. 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
  4141. 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
  4142. 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
  4143. 1.0.13 10 10013 10.so.0.1.0.13
  4144. 1.2.2 12 10202 12.so.0.1.2.2
  4145. 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
  4146. 1.2.3 12 10203 12.so.0.1.2.3
  4147. 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
  4148. 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
  4149. 1.0.14 10 10014 10.so.0.1.0.14
  4150. 1.2.4 13 10204 12.so.0.1.2.4
  4151. 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
  4152. 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
  4153. 1.0.15 10 10015 10.so.0.1.0.15
  4154. 1.2.5 13 10205 12.so.0.1.2.5
  4155. 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
  4156. 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
  4157. 1.0.16 10 10016 10.so.0.1.0.16
  4158. 1.2.6 13 10206 12.so.0.1.2.6
  4159. 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
  4160. 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
  4161. 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
  4162. 1.0.17 10 10017 12.so.0.1.0.17
  4163. 1.2.7 13 10207 12.so.0.1.2.7
  4164. 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
  4165. 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
  4166. 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
  4167. 1.0.18 10 10018 12.so.0.1.0.18
  4168. 1.2.8 13 10208 12.so.0.1.2.8
  4169. 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
  4170. 1.2.9beta4-11 13 10209 12.so.0.9[.0]
  4171. 1.2.9rc1 13 10209 12.so.0.9[.0]
  4172. 1.2.9 13 10209 12.so.0.9[.0]
  4173. 1.2.10beta1-7 13 10210 12.so.0.10[.0]
  4174. 1.2.10rc1-2 13 10210 12.so.0.10[.0]
  4175. 1.2.10 13 10210 12.so.0.10[.0]
  4176. 1.4.0beta1-6 14 10400 14.so.0.0[.0]
  4177. 1.2.11beta1-4 13 10210 12.so.0.11[.0]
  4178. 1.4.0beta7-8 14 10400 14.so.0.0[.0]
  4179. 1.2.11 13 10211 12.so.0.11[.0]
  4180. 1.2.12 13 10212 12.so.0.12[.0]
  4181. 1.4.0beta9-14 14 10400 14.so.0.0[.0]
  4182. 1.2.13 13 10213 12.so.0.13[.0]
  4183. 1.4.0beta15-36 14 10400 14.so.0.0[.0]
  4184. 1.4.0beta37-87 14 10400 14.so.14.0[.0]
  4185. 1.4.0rc01 14 10400 14.so.14.0[.0]
  4186. 1.4.0beta88-109 14 10400 14.so.14.0[.0]
  4187. 1.4.0rc02-08 14 10400 14.so.14.0[.0]
  4188. 1.4.0 14 10400 14.so.14.0[.0]
  4189. 1.4.1beta01-03 14 10401 14.so.14.1[.0]
  4190. 1.4.1rc01 14 10401 14.so.14.1[.0]
  4191. 1.4.1beta04-12 14 10401 14.so.14.1[.0]
  4192. 1.4.1 14 10401 14.so.14.1[.0]
  4193. 1.4.2 14 10402 14.so.14.2[.0]
  4194. 1.4.3 14 10403 14.so.14.3[.0]
  4195. 1.4.4 14 10404 14.so.14.4[.0]
  4196. 1.5.0beta01-58 15 10500 15.so.15.0[.0]
  4197. 1.5.0rc01-07 15 10500 15.so.15.0[.0]
  4198. 1.5.0 15 10500 15.so.15.0[.0]
  4199. 1.5.1beta01-11 15 10501 15.so.15.1[.0]
  4200. 1.5.1rc01-02 15 10501 15.so.15.1[.0]
  4201. 1.5.1 15 10501 15.so.15.1[.0]
  4202. 1.5.2beta01-03 15 10502 15.so.15.2[.0]
  4203. 1.5.2rc01-03 15 10502 15.so.15.2[.0]
  4204. 1.5.2 15 10502 15.so.15.2[.0]
  4205. 1.5.3beta01-10 15 10503 15.so.15.3[.0]
  4206. 1.5.3rc01-02 15 10503 15.so.15.3[.0]
  4207. 1.5.3beta11 15 10503 15.so.15.3[.0]
  4208. 1.5.3 [omitted]
  4209. 1.5.4beta01-08 15 10504 15.so.15.4[.0]
  4210. 1.5.4rc01 15 10504 15.so.15.4[.0]
  4211. 1.5.4 15 10504 15.so.15.4[.0]
  4212. 1.5.5beta01-08 15 10505 15.so.15.5[.0]
  4213. 1.5.5rc01 15 10505 15.so.15.5[.0]
  4214. 1.5.5 15 10505 15.so.15.5[.0]
  4215. 1.5.6beta01-07 15 10506 15.so.15.6[.0]
  4216. 1.5.6rc01-03 15 10506 15.so.15.6[.0]
  4217. 1.5.6 15 10506 15.so.15.6[.0]
  4218. 1.5.7beta01-05 15 10507 15.so.15.7[.0]
  4219. 1.5.7rc01-03 15 10507 15.so.15.7[.0]
  4220. 1.5.7 15 10507 15.so.15.7[.0]
  4221. 1.5.8beta01 15 10508 15.so.15.8[.0]
  4222. 1.5.8rc01 15 10508 15.so.15.8[.0]
  4223. 1.5.8 15 10508 15.so.15.8[.0]
  4224. 1.5.9beta01-02 15 10509 15.so.15.9[.0]
  4225. 1.5.9rc01 15 10509 15.so.15.9[.0]
  4226. 1.5.9 15 10509 15.so.15.9[.0]
  4227. Henceforth the source version will match the shared-library minor
  4228. and patch numbers; the shared-library major version number will be
  4229. used for changes in backward compatibility, as it is intended. The
  4230. PNG_PNGLIB_VER macro, which is not used within libpng but is available
  4231. for applications, is an unsigned integer of the form xyyzz corresponding
  4232. to the source version x.y.z (leading zeros in y and z). Beta versions
  4233. were given the previous public release number plus a letter, until
  4234. version 1.0.6j; from then on they were given the upcoming public
  4235. release number plus "betaNN" or "rcN".
  4236. .SH "SEE ALSO"
  4237. .BR "png"(5), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
  4238. .LP
  4239. .IR libpng :
  4240. .IP
  4241. http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
  4242. http://www.libpng.org/pub/png
  4243. .LP
  4244. .IR zlib :
  4245. .IP
  4246. (generally) at the same location as
  4247. .I libpng
  4248. or at
  4249. .br
  4250. ftp://ftp.info-zip.org/pub/infozip/zlib
  4251. .LP
  4252. .IR PNG specification: RFC 2083
  4253. .IP
  4254. (generally) at the same location as
  4255. .I libpng
  4256. or at
  4257. .br
  4258. ftp://ds.internic.net/rfc/rfc2083.txt
  4259. .br
  4260. or (as a W3C Recommendation) at
  4261. .br
  4262. http://www.w3.org/TR/REC-png.html
  4263. .LP
  4264. In the case of any inconsistency between the PNG specification
  4265. and this library, the specification takes precedence.
  4266. .SH AUTHORS
  4267. This man page: Glenn Randers-Pehrson
  4268. <glennrp at users.sourceforge.net>
  4269. The contributing authors would like to thank all those who helped
  4270. with testing, bug fixes, and patience. This wouldn't have been
  4271. possible without all of you.
  4272. Thanks to Frank J. T. Wojcik for helping with the documentation.
  4273. Libpng version 1.5.9 - February 18, 2012:
  4274. Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
  4275. Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
  4276. Supported by the PNG development group
  4277. .br
  4278. png-mng-implement at lists.sf.net
  4279. (subscription required; visit
  4280. png-mng-implement at lists.sourceforge.net (subscription required; visit
  4281. https://lists.sourceforge.net/lists/listinfo/png-mng-implement
  4282. to subscribe).
  4283. .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
  4284. (This copy of the libpng notices is provided for your convenience. In case of
  4285. any discrepancy between this copy and the notices in the file png.h that is
  4286. included in the libpng distribution, the latter shall prevail.)
  4287. If you modify libpng you may insert additional notices immediately following
  4288. this sentence.
  4289. This code is released under the libpng license.
  4290. libpng versions 1.2.6, August 15, 2004, through 1.5.9, February 18, 2012, are
  4291. Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
  4292. distributed according to the same disclaimer and license as libpng-1.2.5
  4293. with the following individual added to the list of Contributing Authors
  4294. Cosmin Truta
  4295. libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
  4296. Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
  4297. distributed according to the same disclaimer and license as libpng-1.0.6
  4298. with the following individuals added to the list of Contributing Authors
  4299. Simon-Pierre Cadieux
  4300. Eric S. Raymond
  4301. Gilles Vollant
  4302. and with the following additions to the disclaimer:
  4303. There is no warranty against interference with your
  4304. enjoyment of the library or against infringement.
  4305. There is no warranty that our efforts or the library
  4306. will fulfill any of your particular purposes or needs.
  4307. This library is provided with all faults, and the entire
  4308. risk of satisfactory quality, performance, accuracy, and
  4309. effort is with the user.
  4310. libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
  4311. Copyright (c) 1998, 1999 Glenn Randers-Pehrson
  4312. Distributed according to the same disclaimer and license as libpng-0.96,
  4313. with the following individuals added to the list of Contributing Authors:
  4314. Tom Lane
  4315. Glenn Randers-Pehrson
  4316. Willem van Schaik
  4317. libpng versions 0.89, June 1996, through 0.96, May 1997, are
  4318. Copyright (c) 1996, 1997 Andreas Dilger
  4319. Distributed according to the same disclaimer and license as libpng-0.88,
  4320. with the following individuals added to the list of Contributing Authors:
  4321. John Bowler
  4322. Kevin Bracey
  4323. Sam Bushell
  4324. Magnus Holmgren
  4325. Greg Roelofs
  4326. Tom Tanner
  4327. libpng versions 0.5, May 1995, through 0.88, January 1996, are
  4328. Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
  4329. For the purposes of this copyright and license, "Contributing Authors"
  4330. is defined as the following set of individuals:
  4331. Andreas Dilger
  4332. Dave Martindale
  4333. Guy Eric Schalnat
  4334. Paul Schmidt
  4335. Tim Wegner
  4336. The PNG Reference Library is supplied "AS IS". The Contributing Authors
  4337. and Group 42, Inc. disclaim all warranties, expressed or implied,
  4338. including, without limitation, the warranties of merchantability and of
  4339. fitness for any purpose. The Contributing Authors and Group 42, Inc.
  4340. assume no liability for direct, indirect, incidental, special, exemplary,
  4341. or consequential damages, which may result from the use of the PNG
  4342. Reference Library, even if advised of the possibility of such damage.
  4343. Permission is hereby granted to use, copy, modify, and distribute this
  4344. source code, or portions hereof, for any purpose, without fee, subject
  4345. to the following restrictions:
  4346. 1. The origin of this source code must not be misrepresented.
  4347. 2. Altered versions must be plainly marked as such and
  4348. must not be misrepresented as being the original source.
  4349. 3. This Copyright notice may not be removed or altered from
  4350. any source or altered source distribution.
  4351. The Contributing Authors and Group 42, Inc. specifically permit, without
  4352. fee, and encourage the use of this source code as a component to
  4353. supporting the PNG file format in commercial products. If you use this
  4354. source code in a product, acknowledgment is not required but would be
  4355. appreciated.
  4356. A "png_get_copyright" function is available, for convenient use in "about"
  4357. boxes and the like:
  4358. printf("%s",png_get_copyright(NULL));
  4359. Also, the PNG logo (in PNG format, of course) is supplied in the
  4360. files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
  4361. Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
  4362. certification mark of the Open Source Initiative.
  4363. Glenn Randers-Pehrson
  4364. glennrp at users.sourceforge.net
  4365. February 18, 2012
  4366. .\" end of man page