1 .TH LIBPNG 3 "December 15, 2011"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.5.7
11 \fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
15 \fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
19 \fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
23 \fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
27 \fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
31 \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
35 \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
39 \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
43 \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
47 \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
51 \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
55 \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
59 \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
63 \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
67 \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
71 \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
75 \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
79 \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
83 \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
87 \fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
91 \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
95 \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
99 \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
103 \fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
107 \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
111 \fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
115 \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
119 \fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
123 \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
127 \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
131 \fBpng_uint_32 png_get_cHRM_XYZ (png_structp \fIpng_ptr,
133 \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,
135 \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,
137 \fBdouble \fP\fI*blue_Y\fP\fB, double \fI*blue_Z\fP\fB);\fP
141 \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
145 \fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
149 \fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
153 \fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
157 \fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
161 \fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
165 \fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
169 \fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
173 \fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
177 \fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
181 \fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
185 \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
189 \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
193 \fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
197 \fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
201 \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
205 \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
209 \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
213 \fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
217 \fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
221 \fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
225 \fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
229 \fBpng_const_bytep png_get_io_chunk_name (png_structp \fIpng_ptr\fP\fB);\fP
233 \fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
237 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
241 \fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
245 \fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
249 \fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
253 \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
257 \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
261 \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
265 \fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
269 \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
273 \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
277 \fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
281 \fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
285 \fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
289 \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
293 \fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr)
295 \fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
299 \fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
303 \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
307 \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
311 \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
315 \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
319 \fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
323 \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
327 \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
331 \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
335 \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
339 \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
343 \fB/* This function is really an inline macro. \fI*/
345 \fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
349 \fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
353 \fB/* This function is really an inline macro. \fI*/
355 \fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
359 \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
363 \fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
367 \fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
371 \fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
375 \fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
379 \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
383 \fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
387 \fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
391 \fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
395 \fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
399 \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
403 \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
407 \fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
411 \fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
415 \fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
419 \fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
423 \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
427 \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
431 \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
435 \fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
439 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
443 \fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
447 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
451 \fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
455 \fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
459 \fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
463 \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
467 \fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
471 \fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
475 \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
479 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
483 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
487 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
491 \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
495 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
499 \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
503 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
507 \fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
511 \fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
515 \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
519 \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
523 \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
527 \fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
531 \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
535 \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
539 \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
543 \fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
547 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
551 \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
555 \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
559 \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
563 \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,
565 \fBdouble \fP\fIgreen_Z\fP\fB, double \fP\fIblue_X\fP\fB, double \fP\fIblue_Y\fP\fB, double \fIblue_Z\fP\fB);\fP
569 \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
573 \fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
577 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
581 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
585 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
589 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
593 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
597 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
601 \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
605 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
609 \fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
613 \fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
617 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
621 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
625 \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
629 \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
633 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
637 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
641 \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
645 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
649 \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
653 \fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
657 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
661 \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
665 \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
669 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
673 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
677 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
681 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
685 \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
689 \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
693 \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
697 \fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
701 \fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
705 \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
709 \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
713 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
717 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
721 \fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
725 \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
729 \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
733 \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
737 \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
741 \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
745 \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
749 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
753 \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
757 \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
761 \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
765 \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
769 \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
773 \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
777 \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
781 \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
785 \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
789 \fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
793 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
797 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
801 \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
805 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
809 \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
813 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
817 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
821 \fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
825 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
829 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
833 \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
837 \fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
841 \fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
845 \fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
849 \fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
853 \fBvoid \fP\fIpng_set_text_compression_method\fP\fB, (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod)\fP\fB);\fP
857 \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
861 \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
865 \fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
869 \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
873 \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
877 \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
881 \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
885 \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
889 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
893 \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
897 \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
901 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
905 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
909 \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
913 \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
917 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
921 \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
925 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
929 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
933 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
937 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
941 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
945 \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
949 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
953 \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
957 \fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
961 \fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
965 \fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
972 library supports encoding, decoding, and various manipulations of
973 the Portable Network Graphics (PNG) format image files. It uses the
976 Following is a copy of the libpng-manual.txt file that accompanies libpng.
978 libpng-manual.txt - A description on how to use and modify libpng
980 libpng version 1.5.7 - December 15, 2011
981 Updated and distributed by Glenn Randers-Pehrson
982 <glennrp at users.sourceforge.net>
983 Copyright (c) 1998-2011 Glenn Randers-Pehrson
985 This document is released under the libpng license.
986 For conditions of distribution and use, see the disclaimer
991 libpng versions 0.97, January 1998, through 1.5.7 - December 15, 2011
992 Updated and distributed by Glenn Randers-Pehrson
993 Copyright (c) 1998-2011 Glenn Randers-Pehrson
995 libpng 1.0 beta 6 version 0.96 May 28, 1997
996 Updated and distributed by Andreas Dilger
997 Copyright (c) 1996, 1997 Andreas Dilger
999 libpng 1.0 beta 2 - version 0.88 January 26, 1996
1000 For conditions of distribution and use, see copyright
1001 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
1002 Schalnat, Group 42, Inc.
1004 Updated/rewritten per request in the libpng FAQ
1005 Copyright (c) 1995, 1996 Frank J. T. Wojcik
1006 December 18, 1995 & January 20, 1996
1010 This file describes how to use and modify the PNG reference library
1011 (known as libpng) for your own use. There are five sections to this
1012 file: introduction, structures, reading, writing, and modification and
1013 configuration notes for various special platforms. In addition to this
1014 file, example.c is a good starting point for using the library, as
1015 it is heavily commented and should include everything most people
1016 will need. We assume that libpng is already installed; see the
1017 INSTALL file for instructions on how to install libpng.
1019 For examples of libpng usage, see the files "example.c", "pngtest.c",
1020 and the files in the "contrib" directory, all of which are included in
1021 the libpng distribution.
1023 Libpng was written as a companion to the PNG specification, as a way
1024 of reducing the amount of time and effort it takes to support the PNG
1025 file format in application programs.
1027 The PNG specification (second edition), November 2003, is available as
1028 a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
1029 <http://www.w3.org/TR/2003/REC-PNG-20031110/
1030 The W3C and ISO documents have identical technical content.
1032 The PNG-1.2 specification is available at
1033 <http://www.libpng.org/pub/png/documents/>. It is technically equivalent
1034 to the PNG specification (second edition) but has some additional material.
1036 The PNG-1.0 specification is available
1037 as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
1038 W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
1040 Some additional chunks are described in the special-purpose public chunks
1041 documents at <http://www.libpng.org/pub/png/documents/>.
1044 about PNG, and the latest version of libpng, can be found at the PNG home
1045 page, <http://www.libpng.org/pub/png/>.
1047 Most users will not have to modify the library significantly; advanced
1048 users may want to modify it more. All attempts were made to make it as
1049 complete as possible, while keeping the code easy to understand.
1050 Currently, this library only supports C. Support for other languages
1051 is being considered.
1053 Libpng has been designed to handle multiple sessions at one time,
1054 to be easily modifiable, to be portable to the vast majority of
1055 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
1056 to use. The ultimate goal of libpng is to promote the acceptance of
1057 the PNG file format in whatever way possible. While there is still
1058 work to be done (see the TODO file), libpng should cover the
1059 majority of the needs of its users.
1061 Libpng uses zlib for its compression and decompression of PNG files.
1062 Further information about zlib, and the latest version of zlib, can
1063 be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
1064 The zlib compression utility is a general purpose utility that is
1065 useful for more than PNG files, and can be used without libpng.
1066 See the documentation delivered with zlib for more details.
1067 You can usually find the source files for the zlib utility wherever you
1068 find the libpng source files.
1070 Libpng is thread safe, provided the threads are using different
1071 instances of the structures. Each thread should have its own
1072 png_struct and png_info instances, and thus its own image.
1073 Libpng does not protect itself against two threads using the
1074 same instance of a structure.
1078 There are two main structures that are important to libpng, png_struct
1079 and png_info. Both are internal structures that are no longer exposed
1080 in the libpng interface (as of libpng 1.5.0).
1082 The png_info structure is designed to provide information about the
1083 PNG file. At one time, the fields of png_info were intended to be
1084 directly accessible to the user. However, this tended to cause problems
1085 with applications using dynamically loaded libraries, and as a result
1086 a set of interface functions for png_info (the png_get_*() and png_set_*()
1087 functions) was developed, and direct access to the png_info fields was
1090 The png_struct structure is the object used by the library to decode a
1091 single image. As of 1.5.0 this structure is also not exposed.
1093 Almost all libpng APIs require a pointer to a png_struct as the first argument.
1094 Many (in particular the png_set and png_get APIs) also require a pointer
1095 to png_info as the second argument. Some application visible macros
1096 defined in png.h designed for basic data access (reading and writing
1097 integers in the PNG format) don't take a png_info pointer, but it's almost
1098 always safe to assume that a (png_struct*) has to be passed to call an API
1101 You can have more than one png_info structure associated with an image,
1102 as illustrated in pngtest.c, one for information valid prior to the
1103 IDAT chunks and another (called "end_info" below) for things after them.
1105 The png.h header file is an invaluable reference for programming with libpng.
1106 And while I'm on the topic, make sure you include the libpng header file:
1110 and also (as of libpng-1.5.0) the zlib header file, if you need it:
1116 The png.h header file defines a number of integral types used by the
1117 APIs. Most of these are fairly obvious; for example types corresponding
1118 to integers of particular sizes and types for passing color values.
1120 One exception is how non-integral numbers are handled. For application
1121 convenience most APIs that take such numbers have C (double) arguments,
1122 however internally PNG, and libpng, use 32 bit signed integers and encode
1123 the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
1124 macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
1125 which is simply (png_int_32).
1127 All APIs that take (double) arguments also have a matching API that
1128 takes the corresponding fixed point integer arguments. The fixed point
1129 API has the same name as the floating point one with "_fixed" appended.
1130 The actual range of values permitted in the APIs is frequently less than
1131 the full range of (png_fixed_point) (-21474 to +21474). When APIs require
1132 a non-negative argument the type is recorded as png_uint_32 above. Consult
1133 the header file and the text below for more information.
1135 Special care must be take with sCAL chunk handling because the chunk itself
1136 uses non-integral values encoded as strings containing decimal floating point
1137 numbers. See the comments in the header file.
1141 The main header file function declarations are frequently protected by C
1142 preprocessing directives of the form:
1144 #ifdef PNG_feature_SUPPORTED
1148 #ifdef PNG_feature_SUPPORTED
1152 The library can be built without support for these APIs, although a
1153 standard build will have all implemented APIs. Application programs
1154 should check the feature macros before using an API for maximum
1155 portability. From libpng 1.5.0 the feature macros set during the build
1156 of libpng are recorded in the header file "pnglibconf.h" and this file
1157 is always included by png.h.
1159 If you don't need to change the library configuration from the default, skip to
1160 the next section ("Reading").
1162 Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
1163 of the build project files in the 'projects' directory simply copy
1164 scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
1165 systems do not permit easy auto-configuration of the library - they only
1166 support the default configuration.
1168 The easiest way to make minor changes to the libpng configuration when
1169 auto-configuration is supported is to add definitions to the command line
1170 using (typically) CPPFLAGS. For example:
1172 CPPFLAGS=-DPNG_NO_FLOATING_ARITHMETIC
1174 will change the internal libpng math implementation for gamma correction and
1175 other arithmetic calculations to fixed point, avoiding the need for fast
1176 floating point support. The result can be seen in the generated pnglibconf.h -
1177 make sure it contains the changed feature macro setting.
1179 If you need to make more extensive configuration changes - more than one or two
1180 feature macro settings - you can either add -DPNG_USER_CONFIG to the build
1181 command line and put a list of feature macro settings in pngusr.h or you can set
1182 DFA_XTRA (a makefile variable) to a file containing the same information in the
1183 form of 'option' settings.
1185 A. Changing pnglibconf.h
1187 A variety of methods exist to build libpng. Not all of these support
1188 reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
1189 rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
1191 Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
1192 pnglibconf.h and changing the lines defining the supported features, paying
1193 very close attention to the 'option' information in scripts/pnglibconf.dfa
1194 that describes those features and their requirements. This is easy to get
1197 B. Configuration using DFA_XTRA
1199 Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
1200 variant such as 'nawk' or 'gawk', is available. The configure build will
1201 automatically find an appropriate awk and build pnglibconf.h.
1202 The scripts/pnglibconf.mak file contains a set of make rules for doing the
1203 same thing if configure is not used, and many of the makefiles in the scripts
1204 directory use this approach.
1206 When rebuilding simply write a new file containing changed options and set
1207 DFA_XTRA to the name of this file. This causes the build to append the new file
1208 to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
1209 of the following forms:
1213 This turns all optional features off. Include it at the start of pngusr.dfa to
1214 make it easier to build a minimal configuration. You will need to turn at least
1215 some features on afterward to enable either reading or writing code, or both.
1220 Enable or disable a single feature. This will automatically enable other
1221 features required by a feature that is turned on or disable other features that
1222 require a feature which is turned off. Conflicting settings will cause an error
1223 message to be emitted by awk.
1225 setting feature default value
1227 Changes the default value of setting 'feature' to 'value'. There are a small
1228 number of settings listed at the top of pnglibconf.h, they are documented in the
1229 source code. Most of these values have performance implications for the library
1230 but most of them have no visible effect on the API. Some can also be overridden
1233 This method of building a customized pnglibconf.h is illustrated in
1234 contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
1235 pngusr.dfa in these directories.
1237 C. Configuration using PNG_USR_CONFIG
1239 If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the file
1240 pngusr.h will automatically be included before the options in
1241 scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
1242 macro definitions turning features on or off or setting settings.
1244 Apart from the global setting "everything = off" all the options listed above
1245 can be set using macros in pngusr.h:
1247 #define PNG_feature_SUPPORTED
1253 #define PNG_NO_feature
1259 #define PNG_feature value
1263 setting feature default value
1265 Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
1266 pngusr file you supply override the contents of scripts/pnglibconf.dfa
1268 If confusing or incomprehensible behavior results it is possible to
1269 examine the intermediate file pnglibconf.dfn to find the full set of
1270 dependency information for each setting and option. Simply locate the
1271 feature in the file and read the C comments that precede it.
1273 This method is also illustrated in the contrib/pngminim/* makefiles and
1278 We'll now walk you through the possible functions to call when reading
1279 in a PNG file sequentially, briefly explaining the syntax and purpose
1280 of each one. See example.c and png.h for more detail. While
1281 progressive reading is covered in the next section, you will still
1282 need some of the functions discussed in this section to read a PNG
1287 You will want to do the I/O initialization(*) before you get into libpng,
1288 so if it doesn't work, you don't have much to undo. Of course, you
1289 will also want to insure that you are, in fact, dealing with a PNG
1290 file. Libpng provides a simple check to see if a file is a PNG file.
1291 To use it, pass in the first 1 to 8 bytes of the file to the function
1292 png_sig_cmp(), and it will return 0 (false) if the bytes match the
1293 corresponding bytes of the PNG signature, or nonzero (true) otherwise.
1294 Of course, the more bytes you pass in, the greater the accuracy of the
1297 If you are intending to keep the file pointer open for use in libpng,
1298 you must ensure you don't read more than 8 bytes from the beginning
1299 of the file, and you also have to make a call to png_set_sig_bytes_read()
1300 with the number of bytes you read from the beginning. Libpng will
1301 then only check the bytes (if any) that your program didn't read.
1303 (*): If you are not using the standard I/O functions, you will need
1304 to replace them with custom functions. See the discussion under
1308 FILE *fp = fopen(file_name, "rb");
1314 fread(header, 1, number, fp);
1315 is_png = !png_sig_cmp(header, 0, number);
1323 Next, png_struct and png_info need to be allocated and initialized. In
1324 order to ensure that the size of these structures is correct even with a
1325 dynamically linked libpng, there are functions to initialize and
1326 allocate the structures. We also pass the library version, optional
1327 pointers to error handling functions, and a pointer to a data struct for
1328 use by the error functions, if necessary (the pointer and functions can
1329 be NULL if the default error handlers are to be used). See the section
1330 on Changes to Libpng below regarding the old initialization functions.
1331 The structure allocation functions quietly return NULL if they fail to
1332 create the structure, so your application should check for that.
1334 png_structp png_ptr = png_create_read_struct
1335 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1336 user_error_fn, user_warning_fn);
1341 png_infop info_ptr = png_create_info_struct(png_ptr);
1345 png_destroy_read_struct(&png_ptr,
1346 (png_infopp)NULL, (png_infopp)NULL);
1350 If you want to use your own memory allocation routines,
1351 use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
1352 png_create_read_struct_2() instead of png_create_read_struct():
1354 png_structp png_ptr = png_create_read_struct_2
1355 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1356 user_error_fn, user_warning_fn, (png_voidp)
1357 user_mem_ptr, user_malloc_fn, user_free_fn);
1359 The error handling routines passed to png_create_read_struct()
1360 and the memory alloc/free routines passed to png_create_struct_2()
1361 are only necessary if you are not using the libpng supplied error
1362 handling and memory alloc/free functions.
1364 When libpng encounters an error, it expects to longjmp back
1365 to your routine. Therefore, you will need to call setjmp and pass
1366 your png_jmpbuf(png_ptr). If you read the file from different
1367 routines, you will need to update the longjmp buffer every time you enter
1368 a new routine that will call a png_*() function.
1370 See your documentation of setjmp/longjmp for your compiler for more
1371 information on setjmp/longjmp. See the discussion on libpng error
1372 handling in the Customizing Libpng section below for more information
1373 on the libpng error handling. If an error occurs, and libpng longjmp's
1374 back to your setjmp, you will want to call png_destroy_read_struct() to
1377 if (setjmp(png_jmpbuf(png_ptr)))
1379 png_destroy_read_struct(&png_ptr, &info_ptr,
1385 Pass (png_infopp)NULL instead of &end_info if you didn't create
1386 an end_info structure.
1388 If you would rather avoid the complexity of setjmp/longjmp issues,
1389 you can compile libpng with PNG_NO_SETJMP, in which case
1390 errors will result in a call to PNG_ABORT() which defaults to abort().
1392 You can #define PNG_ABORT() to a function that does something
1393 more useful than abort(), as long as your function does not
1396 Now you need to set up the input code. The default for libpng is to
1397 use the C function fread(). If you use this, you will need to pass a
1398 valid FILE * in the function png_init_io(). Be sure that the file is
1399 opened in binary mode. If you wish to handle reading data in another
1400 way, you need not call the png_init_io() function, but you must then
1401 implement the libpng I/O methods discussed in the Customizing Libpng
1404 png_init_io(png_ptr, fp);
1406 If you had previously opened the file and read any of the signature from
1407 the beginning in order to see if this was a PNG file, you need to let
1408 libpng know that there are some bytes missing from the start of the file.
1410 png_set_sig_bytes(png_ptr, number);
1412 You can change the zlib compression buffer size to be used while
1413 reading compressed data with
1415 png_set_compression_buffer_size(png_ptr, buffer_size);
1417 where the default size is 8192 bytes. Note that the buffer size
1418 is changed immediately and the buffer is reallocated immediately,
1419 instead of setting a flag to be acted upon later.
1421 If you want CRC errors to be handled in a different manner than
1424 png_set_crc_action(png_ptr, crit_action, ancil_action);
1426 The values for png_set_crc_action() say how libpng is to handle CRC errors in
1427 ancillary and critical chunks, and whether to use the data contained
1428 therein. Note that it is impossible to "discard" data in a critical
1431 Choices for (int) crit_action are
1432 PNG_CRC_DEFAULT 0 error/quit
1433 PNG_CRC_ERROR_QUIT 1 error/quit
1434 PNG_CRC_WARN_USE 3 warn/use data
1435 PNG_CRC_QUIET_USE 4 quiet/use data
1436 PNG_CRC_NO_CHANGE 5 use the current value
1438 Choices for (int) ancil_action are
1439 PNG_CRC_DEFAULT 0 error/quit
1440 PNG_CRC_ERROR_QUIT 1 error/quit
1441 PNG_CRC_WARN_DISCARD 2 warn/discard data
1442 PNG_CRC_WARN_USE 3 warn/use data
1443 PNG_CRC_QUIET_USE 4 quiet/use data
1444 PNG_CRC_NO_CHANGE 5 use the current value
1446 .SS Setting up callback code
1448 You can set up a callback function to handle any unknown chunks in the
1449 input stream. You must supply the function
1451 read_chunk_callback(png_structp png_ptr,
1452 png_unknown_chunkp chunk);
1454 /* The unknown chunk structure contains your
1455 chunk data, along with similar data for any other
1462 /* Note that libpng has already taken care of
1465 /* put your code here. Search for your chunk in the
1466 unknown chunk structure, process it, and return one
1467 of the following: */
1469 return (-n); /* chunk had an error */
1470 return (0); /* did not recognize */
1471 return (n); /* success */
1474 (You can give your function another name that you like instead of
1475 "read_chunk_callback")
1477 To inform libpng about your function, use
1479 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1480 read_chunk_callback);
1482 This names not only the callback function, but also a user pointer that
1483 you can retrieve with
1485 png_get_user_chunk_ptr(png_ptr);
1487 If you call the png_set_read_user_chunk_fn() function, then all unknown
1488 chunks will be saved when read, in case your callback function will need
1489 one or more of them. This behavior can be changed with the
1490 png_set_keep_unknown_chunks() function, described below.
1492 At this point, you can set up a callback function that will be
1493 called after each row has been read, which you can use to control
1494 a progress meter or the like. It's demonstrated in pngtest.c.
1495 You must supply a function
1497 void read_row_callback(png_structp png_ptr,
1498 png_uint_32 row, int pass);
1500 /* put your code here */
1503 (You can give it another name that you like instead of "read_row_callback")
1505 To inform libpng about your function, use
1507 png_set_read_status_fn(png_ptr, read_row_callback);
1509 When this function is called the row has already been completely processed and
1510 the 'row' and 'pass' refer to the next row to be handled. For the
1511 non-interlaced case the row that was just handled is simply one less than the
1512 passed in row number, and pass will always be 0. For the interlaced case the
1513 same applies unless the row value is 0, in which case the row just handled was
1514 the last one from one of the preceding passes. Because interlacing may skip a
1515 pass you cannot be sure that the preceding pass is just 'pass-1', if you really
1516 need to know what the last pass is record (row,pass) from the callback and use
1517 the last recorded value each time.
1519 As with the user transform you can find the output row using the
1520 PNG_ROW_FROM_PASS_ROW macro.
1522 .SS Unknown-chunk handling
1524 Now you get to set the way the library processes unknown chunks in the
1525 input PNG stream. Both known and unknown chunks will be read. Normal
1526 behavior is that known chunks will be parsed into information in
1527 various info_ptr members while unknown chunks will be discarded. This
1528 behavior can be wasteful if your application will never use some known
1529 chunk types. To change this, you can call:
1531 png_set_keep_unknown_chunks(png_ptr, keep,
1532 chunk_list, num_chunks);
1533 keep - 0: default unknown chunk handling
1534 1: ignore; do not keep
1535 2: keep only if safe-to-copy
1536 3: keep even if unsafe-to-copy
1538 You can use these definitions:
1539 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1540 PNG_HANDLE_CHUNK_NEVER 1
1541 PNG_HANDLE_CHUNK_IF_SAFE 2
1542 PNG_HANDLE_CHUNK_ALWAYS 3
1544 chunk_list - list of chunks affected (a byte string,
1545 five bytes per chunk, NULL or '\0' if
1548 num_chunks - number of chunks affected; if 0, all
1549 unknown chunks are affected. If nonzero,
1550 only the chunks in the list are affected
1552 Unknown chunks declared in this way will be saved as raw data onto a
1553 list of png_unknown_chunk structures. If a chunk that is normally
1554 known to libpng is named in the list, it will be handled as unknown,
1555 according to the "keep" directive. If a chunk is named in successive
1556 instances of png_set_keep_unknown_chunks(), the final instance will
1557 take precedence. The IHDR and IEND chunks should not be named in
1558 chunk_list; if they are, libpng will process them normally anyway.
1559 If you know that your application will never make use of some particular
1560 chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
1562 Here is an example of the usage of png_set_keep_unknown_chunks(),
1563 where the private "vpAg" chunk will later be processed by a user chunk
1566 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1568 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1569 png_byte unused_chunks[]=
1571 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1572 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1573 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1574 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1575 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1576 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1582 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1583 /* ignore all unknown chunks: */
1584 png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
1586 /* except for vpAg: */
1587 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1589 /* also ignore unused known chunks: */
1590 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1591 (int)sizeof(unused_chunks)/5);
1596 The PNG specification allows the width and height of an image to be as
1597 large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1598 Since very few applications really need to process such large images,
1599 we have imposed an arbitrary 1-million limit on rows and columns.
1600 Larger images will be rejected immediately with a png_error() call. If
1601 you wish to change this limit, you can use
1603 png_set_user_limits(png_ptr, width_max, height_max);
1605 to set your own limits, or use width_max = height_max = 0x7fffffffL
1606 to allow all valid dimensions (libpng may reject some very large images
1607 anyway because of potential buffer overflow conditions).
1609 You should put this statement after you create the PNG structure and
1610 before calling png_read_info(), png_read_png(), or png_process_data().
1612 When writing a PNG datastream, put this statement before calling
1613 png_write_info() or png_write_png().
1615 If you need to retrieve the limits that are being applied, use
1617 width_max = png_get_user_width_max(png_ptr);
1618 height_max = png_get_user_height_max(png_ptr);
1620 The PNG specification sets no limit on the number of ancillary chunks
1621 allowed in a PNG datastream. You can impose a limit on the total number
1622 of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
1624 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
1626 where 0x7fffffffL means unlimited. You can retrieve this limit with
1628 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
1630 This limit also applies to the number of buffers that can be allocated
1631 by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks.
1633 You can also set a limit on the amount of memory that a compressed chunk
1634 other than IDAT can occupy, with
1636 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
1638 and you can retrieve the limit with
1640 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
1642 Any chunks that would cause either of these limits to be exceeded will
1645 .SS Information about your system
1647 If you intend to display the PNG or to incorporate it in other image data you
1648 need to tell libpng information about your display or drawing surface so that
1649 libpng can convert the values in the image to match the display.
1651 From libpng-1.5.4 this information can be set before reading the PNG file
1652 header. In earlier versions png_set_gamma() existed but behaved incorrectly if
1653 called before the PNG file header had been read and png_set_alpha_mode() did not
1656 If you need to support versions prior to libpng-1.5.4 test the version number
1657 as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
1658 described in the appropriate manual page.
1660 You give libpng the encoding expected by your system expressed as a 'gamma'
1661 value. You can also specify a default encoding for the PNG file in
1662 case the required information is missing from the file. By default libpng
1663 assumes that the PNG data matches your system, to keep this default call:
1665 png_set_gamma(png_ptr, screen_gamma, 1/screen_gamma/*file gamma*/);
1667 or you can use the fixed point equivalent:
1669 png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma, PNG_FP_1/screen_gamma);
1671 If you don't know the gamma for your system it is probably 2.2 - a good
1672 approximation to the IEC standard for display systems (sRGB). If images are
1673 too contrasty or washed out you got the value wrong - check your system
1676 Many systems permit the system gamma to be changed via a lookup table in the
1677 display driver, a few systems, including older Macs, change the response by
1678 default. As of 1.5.4 three special values are available to handle common
1681 PNG_DEFAULT_sRGB: Indicates that the system conforms to the IEC 61966-2-1
1682 standard. This matches almost all systems.
1683 PNG_GAMMA_MAC_18: Indicates that the system is an older (pre Mac OS 10.6)
1684 Apple Macintosh system with the default settings.
1685 PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates that the
1686 system expects data with no gamma encoding.
1688 You would use the linear (unencoded) value if you need to process the pixel
1689 values further because this avoids the need to decode and reencode each
1690 component value whenever arithmetic is performed. A lot of graphics software
1691 uses linear values for this reason, often with higher precision component values
1692 to preserve overall accuracy.
1694 The second thing you may need to tell libpng about is how your system handles
1695 alpha channel information. Some, but not all, PNG files contain an alpha
1696 channel. To display these files correctly you need to compose the data onto a
1697 suitable background, as described in the PNG specification.
1699 Libpng only supports composing onto a single color (using png_set_background;
1700 see below). Otherwise you must do the composition yourself and, in this case,
1701 you may need to call png_set_alpha_mode:
1703 #if PNG_LIBPNG_VER >= 10504
1704 png_set_alpha_mode(png_ptr, mode, screen_gamma);
1706 png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
1709 The screen_gamma value is the same as the argument to png_set_gamma; however,
1710 how it affects the output depends on the mode. png_set_alpha_mode() sets the
1711 file gamma default to 1/screen_gamma, so normally you don't need to call
1712 png_set_gamma. If you need different defaults call png_set_gamma() before
1713 png_set_alpha_mode() - if you call it after it will override the settings made
1714 by png_set_alpha_mode().
1716 The mode is as follows:
1718 PNG_ALPHA_PNG: The data is encoded according to the PNG specification. Red,
1719 green and blue, or gray, components are gamma encoded color
1720 values and are not premultiplied by the alpha value. The
1721 alpha value is a linear measure of the contribution of the
1722 pixel to the corresponding final output pixel.
1724 You should normally use this format if you intend to perform
1725 color correction on the color values; most, maybe all, color
1726 correction software has no handling for the alpha channel and,
1727 anyway, the math to handle pre-multiplied component values is
1728 unnecessarily complex.
1730 Before you do any arithmetic on the component values you need
1731 to remove the gamma encoding and multiply out the alpha
1732 channel. See the PNG specification for more detail. It is
1733 important to note that when an image with an alpha channel is
1734 scaled, linear encoded, pre-multiplied component values must
1737 The remaining modes assume you don't need to do any further color correction or
1738 that if you do, your color correction software knows all about alpha (it
1741 PNG_ALPHA_STANDARD: The data libpng produces
1742 is encoded in the standard way
1743 assumed by most correctly written graphics software.
1744 The gamma encoding will be removed by libpng and the
1745 linear component values will be pre-multiplied by the
1748 With this format the final image must be re-encoded to
1749 match the display gamma before the image is displayed.
1750 If your system doesn't do that, yet still seems to
1751 perform arithmetic on the pixels without decoding them,
1752 it is broken - check out the modes below.
1754 With PNG_ALPHA_STANDARD libpng always produces linear
1755 component values, whatever screen_gamma you supply. The
1756 screen_gamma value is, however, used as a default for
1757 the file gamma if the PNG file has no gamma information.
1759 If you call png_set_gamma() after png_set_alpha_mode() you
1760 will override the linear encoding. Instead the
1761 pre-multiplied pixel values will be gamma encoded but
1762 the alpha channel will still be linear. This may
1763 actually match the requirements of some broken software,
1766 While linear 8-bit data is often used it has
1767 insufficient precision for any image with a reasonable
1768 dynamic range. To avoid problems, and if your software
1769 supports it, use png_set_expand_16() to force all
1770 components to 16 bits.
1772 PNG_ALPHA_OPTIMIZED: This mode is the same
1773 as PNG_ALPHA_STANDARD except that
1774 completely opaque pixels are gamma encoded according to
1775 the screen_gamma value. Pixels with alpha less than 1.0
1776 will still have linear components.
1778 Use this format if you have control over your
1779 compositing software and do don't do other arithmetic
1780 (such as scaling) on the data you get from libpng. Your
1781 compositing software can simply copy opaque pixels to
1782 the output but still has linear values for the
1785 In normal compositing, where the alpha channel encodes
1786 partial pixel coverage (as opposed to broad area
1787 translucency), the inaccuracies of the 8-bit
1788 representation of non-opaque pixels are irrelevant.
1790 You can also try this format if your software is broken;
1791 it might look better.
1793 PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD;
1794 however, all component values,
1795 including the alpha channel are gamma encoded. This is
1796 an appropriate format to try if your software, or more
1797 likely hardware, is totally broken, i.e., if it performs
1798 linear arithmetic directly on gamma encoded values.
1800 In most cases of broken software or hardware the bug in the final display
1801 manifests as a subtle halo around composited parts of the image. You may not
1802 even perceive this as a halo; the composited part of the image may simply appear
1803 separate from the background, as though it had been cut out of paper and pasted
1806 If you don't have to deal with bugs in software or hardware, or if you can fix
1807 them, there are three recommended ways of using png_set_alpha_mode():
1809 png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
1812 You can do color correction on the result (libpng does not currently
1813 support color correction internally). When you handle the alpha channel
1814 you need to undo the gamma encoding and multiply out the alpha.
1816 png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
1818 png_set_expand_16(png_ptr);
1820 If you are using the high level interface, don't call png_set_expand_16();
1821 instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
1823 With this mode you can't do color correction, but you can do arithmetic,
1824 including composition and scaling, on the data without further processing.
1826 png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
1829 You can avoid the expansion to 16-bit components with this mode, but you
1830 lose the ability to scale the image or perform other linear arithmetic.
1831 All you can do is compose the result onto a matching output. Since this
1832 mode is libpng-specific you also need to write your own composition
1835 If you don't need, or can't handle, the alpha channel you can call
1836 png_set_background() to remove it by compositing against a fixed color. Don't
1837 call png_set_strip_alpha() to do this - it will leave spurious pixel values in
1838 transparent parts of this image.
1840 png_set_background(png_ptr, &background_color,
1841 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
1843 The background_color is an RGB or grayscale value according to the data format
1844 libpng will produce for you. Because you don't yet know the format of the PNG
1845 file, if you call png_set_background at this point you must arrange for the
1846 format produced by libpng to always have 8-bit or 16-bit components and then
1847 store the color as an 8-bit or 16-bit color as appropriate. The color contains
1848 separate gray and RGB component values, so you can let libpng produce gray or
1849 RGB output according to the input format, but low bit depth grayscale images
1850 must always be converted to at least 8-bit format. (Even though low bit depth
1851 grayscale images can't have an alpha channel they can have a transparent
1854 You set the transforms you need later, either as flags to the high level
1855 interface or libpng API calls for the low level interface. For reference the
1856 settings and API calls required are:
1859 PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
1860 png_set_expand(png_ptr); png_set_scale_16(png_ptr);
1862 If you must get exactly the same inaccurate results
1863 produced by default in versions prior to libpng-1.5.4,
1864 use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
1868 PNG_TRANSFORM_EXPAND_16
1869 png_set_expand_16(png_ptr);
1871 In either case palette image data will be expanded to RGB. If you just want
1872 color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
1875 Calling png_set_background before the PNG file header is read will not work
1876 prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
1877 errors it is therefore much safer to call png_set_background after the head has
1878 been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
1879 used with the high level interface.
1881 .SS The high-level read interface
1883 At this point there are two ways to proceed; through the high-level
1884 read interface, or through a sequence of low-level read operations.
1885 You can use the high-level interface if (a) you are willing to read
1886 the entire image into memory, and (b) the input transformations
1887 you want to do are limited to the following set:
1889 PNG_TRANSFORM_IDENTITY No transformation
1890 PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
1892 PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
1893 8-bit less accurately
1894 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1895 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1897 PNG_TRANSFORM_PACKSWAP Change order of packed
1899 PNG_TRANSFORM_EXPAND Perform set_expand()
1900 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1901 PNG_TRANSFORM_SHIFT Normalize pixels to the
1903 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1905 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1907 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1909 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1910 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
1911 to RGB (or GA to RGBA)
1912 PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
1914 (This excludes setting a background color, doing gamma transformation,
1915 quantizing, and setting filler.) If this is the case, simply do this:
1917 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1919 where png_transforms is an integer containing the bitwise OR of some
1920 set of transformation flags. This call is equivalent to png_read_info(),
1921 followed the set of transformations indicated by the transform mask,
1922 then png_read_image(), and finally png_read_end().
1924 (The final parameter of this call is not yet used. Someday it might point
1925 to transformation parameters required by some future input transform.)
1927 You must use png_transforms and not call any png_set_transform() functions
1928 when you use png_read_png().
1930 After you have called png_read_png(), you can retrieve the image data
1933 row_pointers = png_get_rows(png_ptr, info_ptr);
1935 where row_pointers is an array of pointers to the pixel data for each row:
1937 png_bytep row_pointers[height];
1939 If you know your image size and pixel size ahead of time, you can allocate
1940 row_pointers prior to calling png_read_png() with
1942 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1944 "Image is too tall to process in memory");
1946 if (width > PNG_UINT_32_MAX/pixel_size)
1948 "Image is too wide to process in memory");
1950 row_pointers = png_malloc(png_ptr,
1951 height*png_sizeof(png_bytep));
1953 for (int i=0; i<height, i++)
1954 row_pointers[i]=NULL; /* security precaution */
1956 for (int i=0; i<height, i++)
1957 row_pointers[i]=png_malloc(png_ptr,
1960 png_set_rows(png_ptr, info_ptr, &row_pointers);
1962 Alternatively you could allocate your image in one big block and define
1963 row_pointers[i] to point into the proper places in your block.
1965 If you use png_set_rows(), the application is responsible for freeing
1966 row_pointers (and row_pointers[i], if they were separately allocated).
1968 If you don't allocate row_pointers ahead of time, png_read_png() will
1969 do it, and it'll be free'ed by libpng when you call png_destroy_*().
1971 .SS The low-level read interface
1973 If you are going the low-level route, you are now ready to read all
1974 the file information up to the actual image data. You do this with a
1975 call to png_read_info().
1977 png_read_info(png_ptr, info_ptr);
1979 This will process all chunks up to but not including the image data.
1981 This also copies some of the data from the PNG file into the decode structure
1982 for use in later transformations. Important information copied in is:
1984 1) The PNG file gamma from the gAMA chunk. This overwrites the default value
1985 provided by an earlier call to png_set_gamma or png_set_alpha_mode.
1987 2) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
1988 damages the information provided by an earlier call to png_set_background
1989 resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
1991 3) The number of significant bits in each component value. Libpng uses this to
1992 optimize gamma handling by reducing the internal lookup table sizes.
1994 4) The transparent color information from a tRNS chunk. This can be modified by
1995 a later call to png_set_tRNS.
1997 .SS Querying the info structure
1999 Functions are used to get the information from the info_ptr once it
2000 has been read. Note that these fields may not be completely filled
2001 in until png_read_end() has read the chunk data following the image.
2003 png_get_IHDR(png_ptr, info_ptr, &width, &height,
2004 &bit_depth, &color_type, &interlace_type,
2005 &compression_type, &filter_method);
2007 width - holds the width of the image
2008 in pixels (up to 2^31).
2010 height - holds the height of the image
2011 in pixels (up to 2^31).
2013 bit_depth - holds the bit depth of one of the
2014 image channels. (valid values are
2015 1, 2, 4, 8, 16 and depend also on
2016 the color_type. See also
2017 significant bits (sBIT) below).
2019 color_type - describes which color/alpha channels
2022 (bit depths 1, 2, 4, 8, 16)
2023 PNG_COLOR_TYPE_GRAY_ALPHA
2025 PNG_COLOR_TYPE_PALETTE
2026 (bit depths 1, 2, 4, 8)
2029 PNG_COLOR_TYPE_RGB_ALPHA
2032 PNG_COLOR_MASK_PALETTE
2033 PNG_COLOR_MASK_COLOR
2034 PNG_COLOR_MASK_ALPHA
2036 interlace_type - (PNG_INTERLACE_NONE or
2037 PNG_INTERLACE_ADAM7)
2039 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
2042 filter_method - (must be PNG_FILTER_TYPE_BASE
2043 for PNG 1.0, and can also be
2044 PNG_INTRAPIXEL_DIFFERENCING if
2045 the PNG datastream is embedded in
2046 a MNG-1.0 datastream)
2048 Any or all of interlace_type, compression_type, or
2049 filter_method can be NULL if you are
2050 not interested in their values.
2052 Note that png_get_IHDR() returns 32-bit data into
2053 the application's width and height variables.
2054 This is an unsafe situation if these are 16-bit
2055 variables. In such situations, the
2056 png_get_image_width() and png_get_image_height()
2057 functions described below are safer.
2059 width = png_get_image_width(png_ptr,
2062 height = png_get_image_height(png_ptr,
2065 bit_depth = png_get_bit_depth(png_ptr,
2068 color_type = png_get_color_type(png_ptr,
2071 interlace_type = png_get_interlace_type(png_ptr,
2074 compression_type = png_get_compression_type(png_ptr,
2077 filter_method = png_get_filter_type(png_ptr,
2080 channels = png_get_channels(png_ptr, info_ptr);
2082 channels - number of channels of info for the
2083 color type (valid values are 1 (GRAY,
2084 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
2085 4 (RGB_ALPHA or RGB + filler byte))
2087 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
2089 rowbytes - number of bytes needed to hold a row
2091 signature = png_get_signature(png_ptr, info_ptr);
2093 signature - holds the signature read from the
2094 file (if any). The data is kept in
2095 the same offset it would be if the
2096 whole signature were read (i.e. if an
2097 application had already read in 4
2098 bytes of signature before starting
2099 libpng, the remaining 4 bytes would
2100 be in signature[4] through signature[7]
2101 (see png_set_sig_bytes())).
2103 These are also important, but their validity depends on whether the chunk
2104 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
2105 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
2106 data has been read, or zero if it is missing. The parameters to the
2107 png_get_<chunk> are set directly if they are simple data types, or a
2108 pointer into the info_ptr is returned for any complex types.
2110 png_get_PLTE(png_ptr, info_ptr, &palette,
2113 palette - the palette for the file
2114 (array of png_color)
2116 num_palette - number of entries in the palette
2118 png_get_gAMA(png_ptr, info_ptr, &file_gamma);
2119 png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
2121 file_gamma - the gamma at which the file is
2122 written (PNG_INFO_gAMA)
2124 int_file_gamma - 100,000 times the gamma at which the
2127 png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x, &red_y,
2128 &green_x, &green_y, &blue_x, &blue_y)
2129 png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z, &green_X,
2130 &green_Y, &green_Z, &blue_X, &blue_Y, &blue_Z)
2131 png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x, &int_white_y,
2132 &int_red_x, &int_red_y, &int_green_x, &int_green_y,
2133 &int_blue_x, &int_blue_y)
2134 png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
2135 &int_red_Z, &int_green_X, &int_green_Y, &int_green_Z,
2136 &int_blue_X, &int_blue_Y, &int_blue_Z)
2138 {white,red,green,blue}_{x,y}
2139 A color space encoding specified using the chromaticities
2140 of the end points and the white point. (PNG_INFO_cHRM)
2142 {red,green,blue}_{X,Y,Z}
2143 A color space encoding specified using the encoding end
2144 points - the CIE tristimulus specification of the intended
2145 color of the red, green and blue channels in the PNG RGB
2146 data. The white point is simply the sum of the three end
2147 points. (PNG_INFO_cHRM)
2149 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
2151 file_srgb_intent - the rendering intent (PNG_INFO_sRGB)
2152 The presence of the sRGB chunk
2153 means that the pixel data is in the
2154 sRGB color space. This chunk also
2155 implies specific values of gAMA and
2158 png_get_iCCP(png_ptr, info_ptr, &name,
2159 &compression_type, &profile, &proflen);
2161 name - The profile name.
2163 compression_type - The compression type; always
2164 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2165 You may give NULL to this argument to
2168 profile - International Color Consortium color
2169 profile data. May contain NULs.
2171 proflen - length of profile data in bytes.
2173 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
2175 sig_bit - the number of significant bits for
2176 (PNG_INFO_sBIT) each of the gray,
2177 red, green, and blue channels,
2178 whichever are appropriate for the
2179 given color type (png_color_16)
2181 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
2182 &num_trans, &trans_color);
2184 trans_alpha - array of alpha (transparency)
2185 entries for palette (PNG_INFO_tRNS)
2187 num_trans - number of transparent entries
2190 trans_color - graylevel or color sample values of
2191 the single transparent color for
2192 non-paletted images (PNG_INFO_tRNS)
2194 png_get_hIST(png_ptr, info_ptr, &hist);
2197 hist - histogram of palette (array of
2200 png_get_tIME(png_ptr, info_ptr, &mod_time);
2202 mod_time - time image was last modified
2205 png_get_bKGD(png_ptr, info_ptr, &background);
2207 background - background color (of type
2208 png_color_16p) (PNG_VALID_bKGD)
2209 valid 16-bit red, green and blue
2210 values, regardless of color_type
2212 num_comments = png_get_text(png_ptr, info_ptr,
2213 &text_ptr, &num_text);
2215 num_comments - number of comments
2217 text_ptr - array of png_text holding image
2220 text_ptr[i].compression - type of compression used
2221 on "text" PNG_TEXT_COMPRESSION_NONE
2222 PNG_TEXT_COMPRESSION_zTXt
2223 PNG_ITXT_COMPRESSION_NONE
2224 PNG_ITXT_COMPRESSION_zTXt
2226 text_ptr[i].key - keyword for comment. Must contain
2229 text_ptr[i].text - text comments for current
2230 keyword. Can be empty.
2232 text_ptr[i].text_length - length of text string,
2233 after decompression, 0 for iTXt
2235 text_ptr[i].itxt_length - length of itxt string,
2236 after decompression, 0 for tEXt/zTXt
2238 text_ptr[i].lang - language of comment (empty
2239 string for unknown).
2241 text_ptr[i].lang_key - keyword in UTF-8
2242 (empty string for unknown).
2244 Note that the itxt_length, lang, and lang_key
2245 members of the text_ptr structure only exist when the
2246 library is built with iTXt chunk support. Prior to
2247 libpng-1.4.0 the library was built by default without
2248 iTXt support. Also note that when iTXt is supported,
2249 they contain NULL pointers when the "compression"
2250 field contains PNG_TEXT_COMPRESSION_NONE or
2251 PNG_TEXT_COMPRESSION_zTXt.
2253 num_text - number of comments (same as
2254 num_comments; you can put NULL here
2255 to avoid the duplication)
2257 Note while png_set_text() will accept text, language,
2258 and translated keywords that can be NULL pointers, the
2259 structure returned by png_get_text will always contain
2260 regular zero-terminated C strings. They might be
2261 empty strings but they will never be NULL pointers.
2263 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
2266 num_spalettes - number of sPLT chunks read.
2268 palette_ptr - array of palette structures holding
2269 contents of one or more sPLT chunks
2272 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
2275 offset_x - positive offset from the left edge
2276 of the screen (can be negative)
2278 offset_y - positive offset from the top edge
2279 of the screen (can be negative)
2281 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2283 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
2286 res_x - pixels/unit physical resolution in
2289 res_y - pixels/unit physical resolution in
2292 unit_type - PNG_RESOLUTION_UNKNOWN,
2293 PNG_RESOLUTION_METER
2295 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
2298 unit - physical scale units (an integer)
2300 width - width of a pixel in physical scale units
2302 height - height of a pixel in physical scale units
2303 (width and height are doubles)
2305 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
2308 unit - physical scale units (an integer)
2310 width - width of a pixel in physical scale units
2311 (expressed as a string)
2313 height - height of a pixel in physical scale units
2314 (width and height are strings like "2.54")
2316 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
2317 info_ptr, &unknowns)
2319 unknowns - array of png_unknown_chunk
2320 structures holding unknown chunks
2322 unknowns[i].name - name of unknown chunk
2324 unknowns[i].data - data of unknown chunk
2326 unknowns[i].size - size of unknown chunk's data
2328 unknowns[i].location - position of chunk in file
2330 The value of "i" corresponds to the order in which the
2331 chunks were read from the PNG file or inserted with the
2332 png_set_unknown_chunks() function.
2334 The value of "location" is a bitwise "or" of
2336 PNG_HAVE_IHDR (0x01)
2337 PNG_HAVE_PLTE (0x02)
2338 PNG_AFTER_IDAT (0x08)
2340 The data from the pHYs chunk can be retrieved in several convenient
2343 res_x = png_get_x_pixels_per_meter(png_ptr,
2346 res_y = png_get_y_pixels_per_meter(png_ptr,
2349 res_x_and_y = png_get_pixels_per_meter(png_ptr,
2352 res_x = png_get_x_pixels_per_inch(png_ptr,
2355 res_y = png_get_y_pixels_per_inch(png_ptr,
2358 res_x_and_y = png_get_pixels_per_inch(png_ptr,
2361 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
2364 Each of these returns 0 [signifying "unknown"] if
2365 the data is not present or if res_x is 0;
2366 res_x_and_y is 0 if res_x != res_y
2368 Note that because of the way the resolutions are
2369 stored internally, the inch conversions won't
2370 come out to exactly even number. For example,
2371 72 dpi is stored as 0.28346 pixels/meter, and
2372 when this is retrieved it is 71.9988 dpi, so
2373 be sure to round the returned value appropriately
2374 if you want to display a reasonable-looking result.
2376 The data from the oFFs chunk can be retrieved in several convenient
2379 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
2381 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
2383 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
2385 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
2387 Each of these returns 0 [signifying "unknown" if both
2388 x and y are 0] if the data is not present or if the
2389 chunk is present but the unit is the pixel. The
2390 remark about inexact inch conversions applies here
2391 as well, because a value in inches can't always be
2392 converted to microns and back without some loss
2395 For more information, see the
2396 PNG specification for chunk contents. Be careful with trusting
2397 rowbytes, as some of the transformations could increase the space
2398 needed to hold a row (expand, filler, gray_to_rgb, etc.).
2399 See png_read_update_info(), below.
2401 A quick word about text_ptr and num_text. PNG stores comments in
2402 keyword/text pairs, one pair per chunk, with no limit on the number
2403 of text chunks, and a 2^31 byte limit on their size. While there are
2404 suggested keywords, there is no requirement to restrict the use to these
2405 strings. It is strongly suggested that keywords and text be sensible
2406 to humans (that's the point), so don't use abbreviations. Non-printing
2407 symbols are not allowed. See the PNG specification for more details.
2408 There is also no requirement to have text after the keyword.
2410 Keywords should be limited to 79 Latin-1 characters without leading or
2411 trailing spaces, but non-consecutive spaces are allowed within the
2412 keyword. It is possible to have the same keyword any number of times.
2413 The text_ptr is an array of png_text structures, each holding a
2414 pointer to a language string, a pointer to a keyword and a pointer to
2415 a text string. The text string, language code, and translated
2416 keyword may be empty or NULL pointers. The keyword/text
2417 pairs are put into the array in the order that they are received.
2418 However, some or all of the text chunks may be after the image, so, to
2419 make sure you have read all the text chunks, don't mess with these
2420 until after you read the stuff after the image. This will be
2421 mentioned again below in the discussion that goes with png_read_end().
2423 .SS Input transformations
2425 After you've read the header information, you can set up the library
2426 to handle any special transformations of the image data. The various
2427 ways to transform the data will be described in the order that they
2428 should occur. This is important, as some of these change the color
2429 type and/or bit depth of the data, and some others only work on
2430 certain color types and bit depths.
2432 Transformations you request are ignored if they don't have any meaning for a
2433 particular input data format. However some transformations can have an effect
2434 as a result of a previous transformation. If you specify a contradictory set of
2435 transformations, for example both adding and removing the alpha channel, you
2436 cannot predict the final result.
2438 The color used for the transparency values should be supplied in the same
2439 format/depth as the current image data. It is stored in the same format/depth
2440 as the image data in a tRNS chunk, so this is what libpng expects for this data.
2442 The color used for the background value depends on the need_expand argument as
2445 Data will be decoded into the supplied row buffers packed into bytes
2446 unless the library has been told to transform it into another format.
2447 For example, 4 bit/pixel paletted or grayscale data will be returned
2448 2 pixels/byte with the leftmost pixel in the high-order bits of the
2449 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
2450 in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
2451 is called to insert filler bytes, either before or after each RGB triplet.
2452 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
2453 byte of the color value first, unless png_set_scale_16() is called to
2454 transform it to regular RGB RGB triplets, or png_set_filler() or
2455 png_set_add alpha() is called to insert filler bytes, either before or
2456 after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
2457 be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
2458 or png_set_scale_16().
2460 The following code transforms grayscale images of less than 8 to 8 bits,
2461 changes paletted images to RGB, and adds a full alpha channel if there is
2462 transparency information in a tRNS chunk. This is most useful on
2463 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
2464 viewing application that wishes to treat all images in the same way.
2466 if (color_type == PNG_COLOR_TYPE_PALETTE)
2467 png_set_palette_to_rgb(png_ptr);
2469 if (png_get_valid(png_ptr, info_ptr,
2470 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
2472 if (color_type == PNG_COLOR_TYPE_GRAY &&
2473 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
2475 The first two functions are actually aliases for png_set_expand(), added
2476 in libpng version 1.0.4, with the function names expanded to improve code
2477 readability. In some future version they may actually do different
2480 As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
2481 added. It expands the sample depth without changing tRNS to alpha.
2483 As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
2484 png_set_expand(); however, the resultant channels have 16 bits rather than 8.
2485 Use this when the output color or gray channels are made linear to avoid fairly
2486 severe accuracy loss.
2489 png_set_expand_16(png_ptr);
2491 PNG can have files with 16 bits per channel. If you only can handle
2492 8 bits per channel, this will strip the pixels down to 8-bit.
2494 if (bit_depth == 16)
2495 #if PNG_LIBPNG_VER >= 10504
2496 png_set_scale_16(png_ptr);
2498 png_set_strip_16(png_ptr);
2501 (The more accurate "png_set_scale_16()" API became available in libpng version
2504 If you need to process the alpha channel on the image separately from the image
2505 data (for example if you convert it to a bitmap mask) it is possible to have
2506 libpng strip the channel leaving just RGB or gray data:
2508 if (color_type & PNG_COLOR_MASK_ALPHA)
2509 png_set_strip_alpha(png_ptr);
2511 If you strip the alpha channel you need to find some other way of dealing with
2512 the information. If, instead, you want to convert the image to an opaque
2513 version with no alpha channel use png_set_background; see below.
2515 As of libpng version 1.5.2, almost all useful expansions are supported, the
2516 major ommissions are conversion of grayscale to indexed images (which can be
2517 done trivially in the application) and conversion of indexed to grayscale (which
2518 can be done by a trivial manipulation of the palette.)
2520 In the following table, the 01 means grayscale with depth<8, 31 means
2521 indexed with depth<8, other numerals represent the color type, "T" means
2522 the tRNS chunk is present, A means an alpha channel is present, and O
2523 means tRNS or alpha is present but all pixels in the image are opaque.
2525 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
2527 01 - [G] - - - - - - - - - - - - -
2528 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
2529 0 1 G + . . G G G G G G B B GB GB
2530 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
2531 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
2532 2 C P C C C + . . C - - CB CB B B
2533 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
2534 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
2535 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
2536 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
2537 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
2538 4A lA G A T T GA GT GT GA GT GT + BA G GBA
2539 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
2540 6A CA PA CA C C A T tT PA P P C CBA + BA
2541 6O CA PBA CA C C A tT T PA P P CBA C BA +
2544 "+" identifies entries where 'from' and 'to' are the same.
2545 "-" means the transformation is not supported.
2546 "." means nothing is necessary (a tRNS chunk can just be ignored).
2547 "t" means the transformation is obtained by png_set_tRNS.
2548 "A" means the transformation is obtained by png_set_add_alpha().
2549 "X" means the transformation is obtained by png_set_expand().
2550 "1" means the transformation is obtained by
2551 png_set_expand_gray_1_2_4_to_8() (and by png_set_expand() if there
2552 is no transparency in the original or the final format).
2553 "C" means the transformation is obtained by png_set_gray_to_rgb().
2554 "G" means the transformation is obtained by png_set_rgb_to_gray().
2555 "P" means the transformation is obtained by
2556 png_set_expand_palette_to_rgb().
2557 "p" means the transformation is obtained by png_set_packing().
2558 "Q" means the transformation is obtained by png_set_quantize().
2559 "T" means the transformation is obtained by png_set_tRNS_to_alpha().
2560 "B" means the transformation is obtained by png_set_background(), or
2563 When an entry has multiple transforms listed all are required to cause the
2564 right overall transformation. When two transforms are separated by a comma
2565 either will do the job. When transforms are enclosed in [] the transform should
2566 do the job but this is currently unimplemented - a different format will result
2567 if the suggested transformations are used.
2569 In PNG files, the alpha channel in an image
2570 is the level of opacity. If you need the alpha channel in an image to
2571 be the level of transparency instead of opacity, you can invert the
2572 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
2573 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
2574 images) is fully transparent, with
2576 png_set_invert_alpha(png_ptr);
2578 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2579 they can, resulting in, for example, 8 pixels per byte for 1 bit
2580 files. This code expands to 1 pixel per byte without changing the
2581 values of the pixels:
2584 png_set_packing(png_ptr);
2586 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
2587 stored in a PNG image have been "scaled" or "shifted" up to the next
2588 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
2589 to 8 bits/sample in the range [0, 255]). However, it is also possible
2590 to convert the PNG pixel data back to the original bit depth of the
2591 image. This call reduces the pixels back down to the original bit depth:
2593 png_color_8p sig_bit;
2595 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
2596 png_set_shift(png_ptr, sig_bit);
2598 PNG files store 3-color pixels in red, green, blue order. This code
2599 changes the storage of the pixels to blue, green, red:
2601 if (color_type == PNG_COLOR_TYPE_RGB ||
2602 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2603 png_set_bgr(png_ptr);
2605 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
2606 into 4 or 8 bytes for windowing systems that need them in this format:
2608 if (color_type == PNG_COLOR_TYPE_RGB)
2609 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
2611 where "filler" is the 8 or 16-bit number to fill with, and the location is
2612 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
2613 you want the filler before the RGB or after. This transformation
2614 does not affect images that already have full alpha channels. To add an
2615 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
2616 will generate RGBA pixels.
2618 Note that png_set_filler() does not change the color type. If you want
2619 to do that, you can add a true alpha channel with
2621 if (color_type == PNG_COLOR_TYPE_RGB ||
2622 color_type == PNG_COLOR_TYPE_GRAY)
2623 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
2625 where "filler" contains the alpha value to assign to each pixel.
2626 This function was added in libpng-1.2.7.
2628 If you are reading an image with an alpha channel, and you need the
2629 data as ARGB instead of the normal PNG format RGBA:
2631 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2632 png_set_swap_alpha(png_ptr);
2634 For some uses, you may want a grayscale image to be represented as
2635 RGB. This code will do that conversion:
2637 if (color_type == PNG_COLOR_TYPE_GRAY ||
2638 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2639 png_set_gray_to_rgb(png_ptr);
2641 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
2644 if (color_type == PNG_COLOR_TYPE_RGB ||
2645 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2646 png_set_rgb_to_gray(png_ptr, error_action, double red_weight,
2647 double green_weight);
2649 error_action = 1: silently do the conversion
2651 error_action = 2: issue a warning if the original
2652 image has any pixel where
2653 red != green or red != blue
2655 error_action = 3: issue an error and abort the
2656 conversion if the original
2657 image has any pixel where
2658 red != green or red != blue
2660 red_weight: weight of red component
2662 green_weight: weight of green component
2663 If either weight is negative, default
2666 In the corresponding fixed point API the red_weight and green_weight values are
2667 simply scaled by 100,000:
2669 png_set_rgb_to_gray(png_ptr, error_action, png_fixed_point red_weight,
2670 png_fixed_point green_weight);
2672 If you have set error_action = 1 or 2, you can
2673 later check whether the image really was gray, after processing
2674 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
2675 It will return a png_byte that is zero if the image was gray or
2676 1 if there were any non-gray pixels. Background and sBIT data
2677 will be silently converted to grayscale, using the green channel
2678 data for sBIT, regardless of the error_action setting.
2680 The default values come from the PNG file cHRM chunk if present; otherwise, the
2681 defaults correspond to the ITU-R recommendation 709, and also the sRGB color
2682 space, as recommended in the Charles Poynton's Colour FAQ,
2683 <http://www.poynton.com/>, in section 9:
2685 <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
2687 Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
2689 Previous versions of this document, 1998 through 2002, recommended a slightly
2692 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
2694 Libpng uses an integer approximation:
2696 Y = (6968 * R + 23434 * G + 2366 * B)/32768
2698 The calculation is done in a linear colorspace, if the image gamma
2701 The png_set_background() function has been described already; it tells libpng to
2702 composite images with alpha or simple transparency against the supplied
2703 background color. For compatibility with versions of libpng earlier than
2704 libpng-1.5.4 it is recommended that you call the function after reading the file
2705 header, even if you don't want to use the color in a bKGD chunk, if one exists.
2707 If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
2708 you may use this color, or supply another color more suitable for
2709 the current display (e.g., the background color from a web page). You
2710 need to tell libpng how the color is represented, both the format of the
2711 component values in the color (the number of bits) and the gamma encoding of the
2712 color. The function takes two arguments, background_gamma_mode and need_expand
2713 to convey this information, however only two combinations are likely to be
2716 png_color_16 my_background;
2717 png_color_16p image_background;
2719 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
2720 png_set_background(png_ptr, image_background,
2721 PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
2723 png_set_background(png_ptr, &my_background,
2724 PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
2726 The second call was described above - my_background is in the format of the
2727 final, display, output produced by libpng. Because you now know the format of
2728 the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
2729 output and to retain palette images (the palette colors will be modified
2730 appropriately and the tRNS chunk removed.) However, if you are doing this,
2731 take great care not to ask for transformations without checking first that
2734 In the first call the background color has the original bit depth and color type
2735 of the PNG file. So, for palette images the color is supplied as a palette
2736 index and for low bit greyscale images the color is a reduced bit value in
2737 image_background->gray.
2739 If you didn't call png_set_gamma() before reading the file header, for example
2740 if you need your code to remain compatible with older versions of libpng prior
2741 to libpng-1.5.4, this is the place to call it.
2743 Do not call it if you called png_set_alpha_mode(); doing so will damage the
2744 settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
2745 supported then you can certainly do png_set_gamma() before reading the PNG
2748 This API unconditionally sets the screen and file gamma values, so it will
2749 override the value in the PNG file unless it is called before the PNG file
2750 reading starts. For this reason you must always call it with the PNG file
2751 value when you call it in this position:
2753 if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
2754 png_set_gamma(png_ptr, screen_gamma, file_gamma);
2757 png_set_gamma(png_ptr, screen_gamma, 0.45455);
2759 If you need to reduce an RGB file to a paletted file, or if a paletted
2760 file has more entries then will fit on your screen, png_set_quantize()
2761 will do that. Note that this is a simple match quantization that merely
2762 finds the closest color available. This should work fairly well with
2763 optimized palettes, but fairly badly with linear color cubes. If you
2764 pass a palette that is larger than maximum_colors, the file will
2765 reduce the number of colors in the palette so it will fit into
2766 maximum_colors. If there is a histogram, libpng will use it to make
2767 more intelligent choices when reducing the palette. If there is no
2768 histogram, it may not do as good a job.
2770 if (color_type & PNG_COLOR_MASK_COLOR)
2772 if (png_get_valid(png_ptr, info_ptr,
2775 png_uint_16p histogram = NULL;
2777 png_get_hIST(png_ptr, info_ptr,
2779 png_set_quantize(png_ptr, palette, num_palette,
2780 max_screen_colors, histogram, 1);
2785 png_color std_color_cube[MAX_SCREEN_COLORS] =
2788 png_set_quantize(png_ptr, std_color_cube,
2789 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
2794 PNG files describe monochrome as black being zero and white being one.
2795 The following code will reverse this (make black be one and white be
2798 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
2799 png_set_invert_mono(png_ptr);
2801 This function can also be used to invert grayscale and gray-alpha images:
2803 if (color_type == PNG_COLOR_TYPE_GRAY ||
2804 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2805 png_set_invert_mono(png_ptr);
2807 PNG files store 16-bit pixels in network byte order (big-endian,
2808 ie. most significant bits first). This code changes the storage to the
2809 other way (little-endian, i.e. least significant bits first, the
2810 way PCs store them):
2812 if (bit_depth == 16)
2813 png_set_swap(png_ptr);
2815 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2816 need to change the order the pixels are packed into bytes, you can use:
2819 png_set_packswap(png_ptr);
2821 Finally, you can write your own transformation function if none of
2822 the existing ones meets your needs. This is done by setting a callback
2825 png_set_read_user_transform_fn(png_ptr,
2828 You must supply the function
2830 void read_transform_fn(png_structp png_ptr, png_row_infop
2831 row_info, png_bytep data)
2833 See pngtest.c for a working example. Your function will be called
2834 after all of the other transformations have been processed. Take care with
2835 interlaced images if you do the interlace yourself - the width of the row is the
2836 width in 'row_info', not the overall image width.
2838 If supported, libpng provides two information routines that you can use to find
2839 where you are in processing the image:
2841 png_get_current_pass_number(png_structp png_ptr);
2842 png_get_current_row_number(png_structp png_ptr);
2844 Don't try using these outside a transform callback - firstly they are only
2845 supported if user transforms are supported, secondly they may well return
2846 unexpected results unless the row is actually being processed at the moment they
2850 images the value returned is the row in the input sub-image image. Use
2851 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
2852 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
2854 The discussion of interlace handling above contains more information on how to
2857 You can also set up a pointer to a user structure for use by your
2858 callback function, and you can inform libpng that your transform
2859 function will change the number of channels or bit depth with the
2862 png_set_user_transform_info(png_ptr, user_ptr,
2863 user_depth, user_channels);
2865 The user's application, not libpng, is responsible for allocating and
2866 freeing any memory required for the user structure.
2868 You can retrieve the pointer via the function
2869 png_get_user_transform_ptr(). For example:
2871 voidp read_user_transform_ptr =
2872 png_get_user_transform_ptr(png_ptr);
2874 The last thing to handle is interlacing; this is covered in detail below,
2875 but you must call the function here if you want libpng to handle expansion
2876 of the interlaced image.
2878 number_of_passes = png_set_interlace_handling(png_ptr);
2880 After setting the transformations, libpng can update your png_info
2881 structure to reflect any transformations you've requested with this
2884 png_read_update_info(png_ptr, info_ptr);
2886 This is most useful to update the info structure's rowbytes
2887 field so you can use it to allocate your image memory. This function
2888 will also update your palette with the correct screen_gamma and
2889 background if these have been given with the calls above. You may
2890 only call png_read_update_info() once with a particular info_ptr.
2892 After you call png_read_update_info(), you can allocate any
2893 memory you need to hold the image. The row data is simply
2894 raw byte data for all forms of images. As the actual allocation
2895 varies among applications, no example will be given. If you
2896 are allocating one large chunk, you will need to build an
2897 array of pointers to each row, as it will be needed for some
2898 of the functions below.
2900 Remember: Before you call png_read_update_info(), the png_get_*()
2901 functions return the values corresponding to the original PNG image.
2902 After you call png_read_update_info the values refer to the image
2903 that libpng will output. Consequently you must call all the png_set_
2904 functions before you call png_read_update_info(). This is particularly
2905 important for png_set_interlace_handling() - if you are going to call
2906 png_read_update_info() you must call png_set_interlace_handling() before
2907 it unless you want to receive interlaced output.
2909 .SS Reading image data
2911 After you've allocated memory, you can read the image data.
2912 The simplest way to do this is in one function call. If you are
2913 allocating enough memory to hold the whole image, you can just
2914 call png_read_image() and libpng will read in all the image data
2915 and put it in the memory area supplied. You will need to pass in
2916 an array of pointers to each row.
2918 This function automatically handles interlacing, so you don't
2919 need to call png_set_interlace_handling() (unless you call
2920 png_read_update_info()) or call this function multiple times, or any
2921 of that other stuff necessary with png_read_rows().
2923 png_read_image(png_ptr, row_pointers);
2925 where row_pointers is:
2927 png_bytep row_pointers[height];
2929 You can point to void or char or whatever you use for pixels.
2931 If you don't want to read in the whole image at once, you can
2932 use png_read_rows() instead. If there is no interlacing (check
2933 interlace_type == PNG_INTERLACE_NONE), this is simple:
2935 png_read_rows(png_ptr, row_pointers, NULL,
2938 where row_pointers is the same as in the png_read_image() call.
2940 If you are doing this just one row at a time, you can do this with
2941 a single row_pointer instead of an array of row_pointers:
2943 png_bytep row_pointer = row;
2944 png_read_row(png_ptr, row_pointer, NULL);
2946 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2947 get somewhat harder. The only current (PNG Specification version 1.2)
2948 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
2949 a somewhat complicated 2D interlace scheme, known as Adam7, that
2950 breaks down an image into seven smaller images of varying size, based
2951 on an 8x8 grid. This number is defined (from libpng 1.5) as
2952 PNG_INTERLACE_ADAM7_PASSES in png.h
2954 libpng can fill out those images or it can give them to you "as is".
2955 It is almost always better to have libpng handle the interlacing for you.
2956 If you want the images filled out, there are two ways to do that. The one
2957 mentioned in the PNG specification is to expand each pixel to cover
2958 those pixels that have not been read yet (the "rectangle" method).
2959 This results in a blocky image for the first pass, which gradually
2960 smooths out as more pixels are read. The other method is the "sparkle"
2961 method, where pixels are drawn only in their final locations, with the
2962 rest of the image remaining whatever colors they were initialized to
2963 before the start of the read. The first method usually looks better,
2964 but tends to be slower, as there are more pixels to put in the rows.
2966 If, as is likely, you want libpng to expand the images, call this before
2967 calling png_start_read_image() or png_read_update_info():
2969 if (interlace_type == PNG_INTERLACE_ADAM7)
2971 = png_set_interlace_handling(png_ptr);
2973 This will return the number of passes needed. Currently, this is seven,
2974 but may change if another interlace type is added. This function can be
2975 called even if the file is not interlaced, where it will return one pass.
2976 You then need to read the whole image 'number_of_passes' times. Each time
2977 will distribute the pixels from the current pass to the correct place in
2978 the output image, so you need to supply the same rows to png_read_rows in
2981 If you are not going to display the image after each pass, but are
2982 going to wait until the entire image is read in, use the sparkle
2983 effect. This effect is faster and the end result of either method
2984 is exactly the same. If you are planning on displaying the image
2985 after each pass, the "rectangle" effect is generally considered the
2988 If you only want the "sparkle" effect, just call png_read_rows() as
2989 normal, with the third parameter NULL. Make sure you make pass over
2990 the image number_of_passes times, and you don't change the data in the
2991 rows between calls. You can change the locations of the data, just
2992 not the data. Each pass only writes the pixels appropriate for that
2993 pass, and assumes the data from previous passes is still valid.
2995 png_read_rows(png_ptr, row_pointers, NULL,
2998 If you only want the first effect (the rectangles), do the same as
2999 before except pass the row buffer in the third parameter, and leave
3000 the second parameter NULL.
3002 png_read_rows(png_ptr, NULL, row_pointers,
3005 If you don't want libpng to handle the interlacing details, just call
3006 png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
3007 Each of the images is a valid image by itself, however you will almost
3008 certainly need to distribute the pixels from each sub-image to the
3009 correct place. This is where everything gets very tricky.
3011 If you want to retrieve the separate images you must pass the correct
3012 number of rows to each successive call of png_read_rows(). The calculation
3013 gets pretty complicated for small images, where some sub-images may
3014 not even exist because either their width or height ends up zero.
3015 libpng provides two macros to help you in 1.5 and later versions:
3017 png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
3018 png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
3020 Respectively these tell you the width and height of the sub-image
3021 corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
3022 this can be confusing because the specification refers to the same passes
3023 as 1 to 7! Be careful, you must check both the width and height before
3024 calling png_read_rows() and not call it for that pass if either is zero.
3026 You can, of course, read each sub-image row by row. If you want to
3027 produce optimal code to make a pixel-by-pixel transformation of an
3028 interlaced image this is the best approach; read each row of each pass,
3029 transform it, and write it out to a new interlaced image.
3031 If you want to de-interlace the image yourself libpng provides further
3032 macros to help that tell you where to place the pixels in the output image.
3033 Because the interlacing scheme is rectangular - sub-image pixels are always
3034 arranged on a rectangular grid - all you need to know for each pass is the
3035 starting column and row in the output image of the first pixel plus the
3036 spacing between each pixel. As of libpng 1.5 there are four macros to
3037 retrieve this information:
3039 png_uint_32 x = PNG_PASS_START_COL(pass);
3040 png_uint_32 y = PNG_PASS_START_ROW(pass);
3041 png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
3042 png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
3044 These allow you to write the obvious loop:
3046 png_uint_32 input_y = 0;
3047 png_uint_32 output_y = PNG_PASS_START_ROW(pass);
3049 while (output_y < output_image_height)
3051 png_uint_32 input_x = 0;
3052 png_uint_32 output_x = PNG_PASS_START_COL(pass);
3054 while (output_x < output_image_width)
3056 image[output_y][output_x] =
3057 subimage[pass][input_y][input_x++];
3066 Notice that the steps between successive output rows and columns are
3067 returned as shifts. This is possible because the pixels in the subimages
3068 are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
3069 image. In practice you may need to directly calculate the output coordinate
3070 given an input coordinate. libpng provides two further macros for this
3073 png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
3074 png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
3076 Finally a pair of macros are provided to tell you if a particular image
3077 row or column appears in a given pass:
3079 int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
3080 int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
3082 Bear in mind that you will probably also need to check the width and height
3083 of the pass in addition to the above to be sure the pass even exists!
3085 With any luck you are convinced by now that you don't want to do your own
3086 interlace handling. In reality normally the only good reason for doing this
3087 is if you are processing PNG files on a pixel-by-pixel basis and don't want
3088 to load the whole file into memory when it is interlaced.
3090 libpng includes a test program, pngvalid, that illustrates reading and
3091 writing of interlaced images. If you can't get interlacing to work in your
3092 code and don't want to leave it to libpng (the recommended approach), see
3093 how pngvalid.c does it.
3095 .SS Finishing a sequential read
3097 After you are finished reading the image through the
3098 low-level interface, you can finish reading the file. If you are
3099 interested in comments or time, which may be stored either before or
3100 after the image data, you should pass the separate png_info struct if
3101 you want to keep the comments from before and after the image
3104 png_infop end_info = png_create_info_struct(png_ptr);
3108 png_destroy_read_struct(&png_ptr, &info_ptr,
3113 png_read_end(png_ptr, end_info);
3115 If you are not interested, you should still call png_read_end()
3116 but you can pass NULL, avoiding the need to create an end_info structure.
3118 png_read_end(png_ptr, (png_infop)NULL);
3120 If you don't call png_read_end(), then your file pointer will be
3121 left pointing to the first chunk after the last IDAT, which is probably
3122 not what you want if you expect to read something beyond the end of
3125 When you are done, you can free all memory allocated by libpng like this:
3127 png_destroy_read_struct(&png_ptr, &info_ptr,
3130 or, if you didn't create an end_info structure,
3132 png_destroy_read_struct(&png_ptr, &info_ptr,
3135 It is also possible to individually free the info_ptr members that
3136 point to libpng-allocated storage with the following function:
3138 png_free_data(png_ptr, info_ptr, mask, seq)
3140 mask - identifies data to be freed, a mask
3141 containing the bitwise OR of one or
3143 PNG_FREE_PLTE, PNG_FREE_TRNS,
3144 PNG_FREE_HIST, PNG_FREE_ICCP,
3145 PNG_FREE_PCAL, PNG_FREE_ROWS,
3146 PNG_FREE_SCAL, PNG_FREE_SPLT,
3147 PNG_FREE_TEXT, PNG_FREE_UNKN,
3148 or simply PNG_FREE_ALL
3150 seq - sequence number of item to be freed
3153 This function may be safely called when the relevant storage has
3154 already been freed, or has not yet been allocated, or was allocated
3155 by the user and not by libpng, and will in those cases do nothing.
3156 The "seq" parameter is ignored if only one item of the selected data
3157 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
3158 are allowed for the data type identified in the mask, such as text or
3159 sPLT, only the n'th item in the structure is freed, where n is "seq".
3161 The default behavior is only to free data that was allocated internally
3162 by libpng. This can be changed, so that libpng will not free the data,
3163 or so that it will free data that was allocated by the user with png_malloc()
3164 or png_zalloc() and passed in via a png_set_*() function, with
3166 png_data_freer(png_ptr, info_ptr, freer, mask)
3169 PNG_DESTROY_WILL_FREE_DATA
3170 PNG_SET_WILL_FREE_DATA
3171 PNG_USER_WILL_FREE_DATA
3173 mask - which data elements are affected
3174 same choices as in png_free_data()
3176 This function only affects data that has already been allocated.
3177 You can call this function after reading the PNG data but before calling
3178 any png_set_*() functions, to control whether the user or the png_set_*()
3179 function is responsible for freeing any existing data that might be present,
3180 and again after the png_set_*() functions to control whether the user
3181 or png_destroy_*() is supposed to free the data. When the user assumes
3182 responsibility for libpng-allocated data, the application must use
3183 png_free() to free it, and when the user transfers responsibility to libpng
3184 for data that the user has allocated, the user must have used png_malloc()
3185 or png_zalloc() to allocate it.
3187 If you allocated your row_pointers in a single block, as suggested above in
3188 the description of the high level read interface, you must not transfer
3189 responsibility for freeing it to the png_set_rows or png_read_destroy function,
3190 because they would also try to free the individual row_pointers[i].
3192 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3193 separately, do not transfer responsibility for freeing text_ptr to libpng,
3194 because when libpng fills a png_text structure it combines these members with
3195 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3196 if you transfer responsibility for free'ing text_ptr from libpng to your
3197 application, your application must not separately free those members.
3199 The png_free_data() function will turn off the "valid" flag for anything
3200 it frees. If you need to turn the flag off for a chunk that was freed by
3201 your application instead of by libpng, you can use
3203 png_set_invalid(png_ptr, info_ptr, mask);
3205 mask - identifies the chunks to be made invalid,
3206 containing the bitwise OR of one or
3208 PNG_INFO_gAMA, PNG_INFO_sBIT,
3209 PNG_INFO_cHRM, PNG_INFO_PLTE,
3210 PNG_INFO_tRNS, PNG_INFO_bKGD,
3211 PNG_INFO_hIST, PNG_INFO_pHYs,
3212 PNG_INFO_oFFs, PNG_INFO_tIME,
3213 PNG_INFO_pCAL, PNG_INFO_sRGB,
3214 PNG_INFO_iCCP, PNG_INFO_sPLT,
3215 PNG_INFO_sCAL, PNG_INFO_IDAT
3217 For a more compact example of reading a PNG image, see the file example.c.
3219 .SS Reading PNG files progressively
3221 The progressive reader is slightly different then the non-progressive
3222 reader. Instead of calling png_read_info(), png_read_rows(), and
3223 png_read_end(), you make one call to png_process_data(), which calls
3224 callbacks when it has the info, a row, or the end of the image. You
3225 set up these callbacks with png_set_progressive_read_fn(). You don't
3226 have to worry about the input/output functions of libpng, as you are
3227 giving the library the data directly in png_process_data(). I will
3228 assume that you have read the section on reading PNG files above,
3229 so I will only highlight the differences (although I will show
3232 png_structp png_ptr;
3235 /* An example code fragment of how you would
3236 initialize the progressive reader in your
3239 initialize_png_reader()
3241 png_ptr = png_create_read_struct
3242 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3243 user_error_fn, user_warning_fn);
3248 info_ptr = png_create_info_struct(png_ptr);
3252 png_destroy_read_struct(&png_ptr,
3253 (png_infopp)NULL, (png_infopp)NULL);
3257 if (setjmp(png_jmpbuf(png_ptr)))
3259 png_destroy_read_struct(&png_ptr, &info_ptr,
3264 /* This one's new. You can provide functions
3265 to be called when the header info is valid,
3266 when each row is completed, and when the image
3267 is finished. If you aren't using all functions,
3268 you can specify NULL parameters. Even when all
3269 three functions are NULL, you need to call
3270 png_set_progressive_read_fn(). You can use
3271 any struct as the user_ptr (cast to a void pointer
3272 for the function call), and retrieve the pointer
3273 from inside the callbacks using the function
3275 png_get_progressive_ptr(png_ptr);
3277 which will return a void pointer, which you have
3278 to cast appropriately.
3280 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
3281 info_callback, row_callback, end_callback);
3286 /* A code fragment that you call as you receive blocks
3289 process_data(png_bytep buffer, png_uint_32 length)
3291 if (setjmp(png_jmpbuf(png_ptr)))
3293 png_destroy_read_struct(&png_ptr, &info_ptr,
3298 /* This one's new also. Simply give it a chunk
3299 of data from the file stream (in order, of
3300 course). On machines with segmented memory
3301 models machines, don't give it any more than
3302 64K. The library seems to run fine with sizes
3303 of 4K. Although you can give it much less if
3304 necessary (I assume you can give it chunks of
3305 1 byte, I haven't tried less then 256 bytes
3306 yet). When this function returns, you may
3307 want to display any rows that were generated
3308 in the row callback if you don't already do
3311 png_process_data(png_ptr, info_ptr, buffer, length);
3313 /* At this point you can call png_process_data_skip if
3314 you want to handle data the library will skip yourself;
3315 it simply returns the number of bytes to skip (and stops
3316 libpng skipping that number of bytes on the next
3317 png_process_data call).
3321 /* This function is called (as set by
3322 png_set_progressive_read_fn() above) when enough data
3323 has been supplied so all of the header has been
3327 info_callback(png_structp png_ptr, png_infop info)
3329 /* Do any setup here, including setting any of
3330 the transformations mentioned in the Reading
3331 PNG files section. For now, you _must_ call
3332 either png_start_read_image() or
3333 png_read_update_info() after all the
3334 transformations are set (even if you don't set
3335 any). You may start getting rows before
3336 png_process_data() returns, so this is your
3337 last chance to prepare for that.
3339 This is where you turn on interlace handling,
3340 assuming you don't want to do it yourself.
3342 If you need to you can stop the processing of
3343 your original input data at this point by calling
3344 png_process_data_pause. This returns the number
3345 of unprocessed bytes from the last png_process_data
3346 call - it is up to you to ensure that the next call
3347 sees these bytes again. If you don't want to bother
3348 with this you can get libpng to cache the unread
3349 bytes by setting the 'save' parameter (see png.h) but
3350 then libpng will have to copy the data internally.
3354 /* This function is called when each row of image
3357 row_callback(png_structp png_ptr, png_bytep new_row,
3358 png_uint_32 row_num, int pass)
3360 /* If the image is interlaced, and you turned
3361 on the interlace handler, this function will
3362 be called for every row in every pass. Some
3363 of these rows will not be changed from the
3364 previous pass. When the row is not changed,
3365 the new_row variable will be NULL. The rows
3366 and passes are called in order, so you don't
3367 really need the row_num and pass, but I'm
3368 supplying them because it may make your life
3371 If you did not turn on interlace handling then
3372 the callback is called for each row of each
3373 sub-image when the image is interlaced. In this
3374 case 'row_num' is the row in the sub-image, not
3375 the row in the output image as it is in all other
3378 For the non-NULL rows of interlaced images when
3379 you have switched on libpng interlace handling,
3380 you must call png_progressive_combine_row()
3381 passing in the row and the old row. You can
3382 call this function for NULL rows (it will just
3383 return) and for non-interlaced images (it just
3384 does the memcpy for you) if it will make the
3385 code easier. Thus, you can just do this for
3386 all cases if you switch on interlace handling;
3389 png_progressive_combine_row(png_ptr, old_row,
3392 /* where old_row is what was displayed for
3393 previously for the row. Note that the first
3394 pass (pass == 0, really) will completely cover
3395 the old row, so the rows do not have to be
3396 initialized. After the first pass (and only
3397 for interlaced images), you will have to pass
3398 the current row, and the function will combine
3399 the old row and the new row.
3401 You can also call png_process_data_pause in this
3402 callback - see above.
3407 end_callback(png_structp png_ptr, png_infop info)
3409 /* This function is called after the whole image
3410 has been read, including any chunks after the
3411 image (up to and including the IEND). You
3412 will usually have the same info chunk as you
3413 had in the header, although some data may have
3414 been added to the comments and time fields.
3416 Most people won't do much here, perhaps setting
3417 a flag that marks the image as finished.
3425 Much of this is very similar to reading. However, everything of
3426 importance is repeated here, so you won't have to constantly look
3427 back up in the reading section to understand writing.
3431 You will want to do the I/O initialization before you get into libpng,
3432 so if it doesn't work, you don't have anything to undo. If you are not
3433 using the standard I/O functions, you will need to replace them with
3434 custom writing functions. See the discussion under Customizing libpng.
3436 FILE *fp = fopen(file_name, "wb");
3441 Next, png_struct and png_info need to be allocated and initialized.
3442 As these can be both relatively large, you may not want to store these
3443 on the stack, unless you have stack space to spare. Of course, you
3444 will want to check if they return NULL. If you are also reading,
3445 you won't want to name your read structure and your write structure
3446 both "png_ptr"; you can call them anything you like, such as
3447 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
3449 png_structp png_ptr = png_create_write_struct
3450 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3451 user_error_fn, user_warning_fn);
3456 png_infop info_ptr = png_create_info_struct(png_ptr);
3459 png_destroy_write_struct(&png_ptr,
3464 If you want to use your own memory allocation routines,
3465 define PNG_USER_MEM_SUPPORTED and use
3466 png_create_write_struct_2() instead of png_create_write_struct():
3468 png_structp png_ptr = png_create_write_struct_2
3469 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3470 user_error_fn, user_warning_fn, (png_voidp)
3471 user_mem_ptr, user_malloc_fn, user_free_fn);
3473 After you have these structures, you will need to set up the
3474 error handling. When libpng encounters an error, it expects to
3475 longjmp() back to your routine. Therefore, you will need to call
3476 setjmp() and pass the png_jmpbuf(png_ptr). If you
3477 write the file from different routines, you will need to update
3478 the png_jmpbuf(png_ptr) every time you enter a new routine that will
3479 call a png_*() function. See your documentation of setjmp/longjmp
3480 for your compiler for more information on setjmp/longjmp. See
3481 the discussion on libpng error handling in the Customizing Libpng
3482 section below for more information on the libpng error handling.
3484 if (setjmp(png_jmpbuf(png_ptr)))
3486 png_destroy_write_struct(&png_ptr, &info_ptr);
3493 If you would rather avoid the complexity of setjmp/longjmp issues,
3494 you can compile libpng with PNG_NO_SETJMP, in which case
3495 errors will result in a call to PNG_ABORT() which defaults to abort().
3497 You can #define PNG_ABORT() to a function that does something
3498 more useful than abort(), as long as your function does not
3501 Now you need to set up the output code. The default for libpng is to
3502 use the C function fwrite(). If you use this, you will need to pass a
3503 valid FILE * in the function png_init_io(). Be sure that the file is
3504 opened in binary mode. Again, if you wish to handle writing data in
3505 another way, see the discussion on libpng I/O handling in the Customizing
3506 Libpng section below.
3508 png_init_io(png_ptr, fp);
3510 If you are embedding your PNG into a datastream such as MNG, and don't
3511 want libpng to write the 8-byte signature, or if you have already
3512 written the signature in your application, use
3514 png_set_sig_bytes(png_ptr, 8);
3516 to inform libpng that it should not write a signature.
3520 At this point, you can set up a callback function that will be
3521 called after each row has been written, which you can use to control
3522 a progress meter or the like. It's demonstrated in pngtest.c.
3523 You must supply a function
3525 void write_row_callback(png_structp png_ptr, png_uint_32 row,
3528 /* put your code here */
3531 (You can give it another name that you like instead of "write_row_callback")
3533 To inform libpng about your function, use
3535 png_set_write_status_fn(png_ptr, write_row_callback);
3537 When this function is called the row has already been completely processed and
3538 it has also been written out. The 'row' and 'pass' refer to the next row to be
3540 non-interlaced case the row that was just handled is simply one less than the
3541 passed in row number, and pass will always be 0. For the interlaced case the
3542 same applies unless the row value is 0, in which case the row just handled was
3543 the last one from one of the preceding passes. Because interlacing may skip a
3544 pass you cannot be sure that the preceding pass is just 'pass-1', if you really
3545 need to know what the last pass is record (row,pass) from the callback and use
3546 the last recorded value each time.
3548 As with the user transform you can find the output row using the
3549 PNG_ROW_FROM_PASS_ROW macro.
3551 You now have the option of modifying how the compression library will
3552 run. The following functions are mainly for testing, but may be useful
3553 in some cases, like if you need to write PNG files extremely fast and
3554 are willing to give up some compression, or if you want to get the
3555 maximum possible compression at the expense of slower writing. If you
3556 have no special needs in this area, let the library do what it wants by
3557 not calling this function at all, as it has been tuned to deliver a good
3558 speed/compression ratio. The second parameter to png_set_filter() is
3559 the filter method, for which the only valid values are 0 (as of the
3560 July 1999 PNG specification, version 1.2) or 64 (if you are writing
3561 a PNG datastream that is to be embedded in a MNG datastream). The third
3562 parameter is a flag that indicates which filter type(s) are to be tested
3563 for each scanline. See the PNG specification for details on the specific
3567 /* turn on or off filtering, and/or choose
3568 specific filters. You can use either a single
3569 PNG_FILTER_VALUE_NAME or the bitwise OR of one
3570 or more PNG_FILTER_NAME masks.
3572 png_set_filter(png_ptr, 0,
3573 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
3574 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
3575 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
3576 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
3577 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
3580 If an application wants to start and stop using particular filters during
3581 compression, it should start out with all of the filters (to ensure that
3582 the previous row of pixels will be stored in case it's needed later),
3583 and then add and remove them after the start of compression.
3585 If you are writing a PNG datastream that is to be embedded in a MNG
3586 datastream, the second parameter can be either 0 or 64.
3588 The png_set_compression_*() functions interface to the zlib compression
3589 library, and should mostly be ignored unless you really know what you are
3590 doing. The only generally useful call is png_set_compression_level()
3591 which changes how much time zlib spends on trying to compress the image
3592 data. See the Compression Library (zlib.h and algorithm.txt, distributed
3593 with zlib) for details on the compression levels.
3597 /* Set the zlib compression level */
3598 png_set_compression_level(png_ptr,
3599 Z_BEST_COMPRESSION);
3601 /* Set other zlib parameters for compressing IDAT */
3602 png_set_compression_mem_level(png_ptr, 8);
3603 png_set_compression_strategy(png_ptr,
3604 Z_DEFAULT_STRATEGY);
3605 png_set_compression_window_bits(png_ptr, 15);
3606 png_set_compression_method(png_ptr, 8);
3607 png_set_compression_buffer_size(png_ptr, 8192)
3609 /* Set zlib parameters for text compression
3610 * If you don't call these, the parameters
3611 * fall back on those defined for IDAT chunks
3613 png_set_text_compression_mem_level(png_ptr, 8);
3614 png_set_text_compression_strategy(png_ptr,
3615 Z_DEFAULT_STRATEGY);
3616 png_set_text_compression_window_bits(png_ptr, 15);
3617 png_set_text_compression_method(png_ptr, 8);
3619 .SS Setting the contents of info for output
3621 You now need to fill in the png_info structure with all the data you
3622 wish to write before the actual image. Note that the only thing you
3623 are allowed to write after the image is the text chunks and the time
3624 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
3625 the latest PNG specification for more information on that. If you
3626 wish to write them before the image, fill them in now, and flag that
3627 data as being valid. If you want to wait until after the data, don't
3628 fill them until png_write_end(). For all the fields in png_info and
3629 their data types, see png.h. For explanations of what the fields
3630 contain, see the PNG specification.
3632 Some of the more important parts of the png_info are:
3634 png_set_IHDR(png_ptr, info_ptr, width, height,
3635 bit_depth, color_type, interlace_type,
3636 compression_type, filter_method)
3638 width - holds the width of the image
3639 in pixels (up to 2^31).
3641 height - holds the height of the image
3642 in pixels (up to 2^31).
3644 bit_depth - holds the bit depth of one of the
3646 (valid values are 1, 2, 4, 8, 16
3647 and depend also on the
3648 color_type. See also significant
3651 color_type - describes which color/alpha
3652 channels are present.
3654 (bit depths 1, 2, 4, 8, 16)
3655 PNG_COLOR_TYPE_GRAY_ALPHA
3657 PNG_COLOR_TYPE_PALETTE
3658 (bit depths 1, 2, 4, 8)
3661 PNG_COLOR_TYPE_RGB_ALPHA
3664 PNG_COLOR_MASK_PALETTE
3665 PNG_COLOR_MASK_COLOR
3666 PNG_COLOR_MASK_ALPHA
3668 interlace_type - PNG_INTERLACE_NONE or
3671 compression_type - (must be
3672 PNG_COMPRESSION_TYPE_DEFAULT)
3674 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
3675 or, if you are writing a PNG to
3676 be embedded in a MNG datastream,
3678 PNG_INTRAPIXEL_DIFFERENCING)
3680 If you call png_set_IHDR(), the call must appear before any of the
3681 other png_set_*() functions, because they might require access to some of
3682 the IHDR settings. The remaining png_set_*() functions can be called
3685 If you wish, you can reset the compression_type, interlace_type, or
3686 filter_method later by calling png_set_IHDR() again; if you do this, the
3687 width, height, bit_depth, and color_type must be the same in each call.
3689 png_set_PLTE(png_ptr, info_ptr, palette,
3692 palette - the palette for the file
3693 (array of png_color)
3694 num_palette - number of entries in the palette
3696 png_set_gAMA(png_ptr, info_ptr, file_gamma);
3697 png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
3699 file_gamma - the gamma at which the image was
3700 created (PNG_INFO_gAMA)
3702 int_file_gamma - 100,000 times the gamma at which
3703 the image was created
3705 png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
3706 green_x, green_y, blue_x, blue_y)
3707 png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
3708 green_Y, green_Z, blue_X, blue_Y, blue_Z)
3709 png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
3710 int_red_x, int_red_y, int_green_x, int_green_y,
3711 int_blue_x, int_blue_y)
3712 png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
3713 int_red_Z, int_green_X, int_green_Y, int_green_Z,
3714 int_blue_X, int_blue_Y, int_blue_Z)
3716 {white,red,green,blue}_{x,y}
3717 A color space encoding specified using the chromaticities
3718 of the end points and the white point.
3720 {red,green,blue}_{X,Y,Z}
3721 A color space encoding specified using the encoding end
3722 points - the CIE tristimulus specification of the intended
3723 color of the red, green and blue channels in the PNG RGB
3724 data. The white point is simply the sum of the three end
3727 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
3729 srgb_intent - the rendering intent
3730 (PNG_INFO_sRGB) The presence of
3731 the sRGB chunk means that the pixel
3732 data is in the sRGB color space.
3733 This chunk also implies specific
3734 values of gAMA and cHRM. Rendering
3735 intent is the CSS-1 property that
3736 has been defined by the International
3738 (http://www.color.org).
3740 PNG_sRGB_INTENT_SATURATION,
3741 PNG_sRGB_INTENT_PERCEPTUAL,
3742 PNG_sRGB_INTENT_ABSOLUTE, or
3743 PNG_sRGB_INTENT_RELATIVE.
3746 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
3749 srgb_intent - the rendering intent
3750 (PNG_INFO_sRGB) The presence of the
3751 sRGB chunk means that the pixel
3752 data is in the sRGB color space.
3753 This function also causes gAMA and
3754 cHRM chunks with the specific values
3755 that are consistent with sRGB to be
3758 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
3761 name - The profile name.
3763 compression_type - The compression type; always
3764 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
3765 You may give NULL to this argument to
3768 profile - International Color Consortium color
3769 profile data. May contain NULs.
3771 proflen - length of profile data in bytes.
3773 png_set_sBIT(png_ptr, info_ptr, sig_bit);
3775 sig_bit - the number of significant bits for
3776 (PNG_INFO_sBIT) each of the gray, red,
3777 green, and blue channels, whichever are
3778 appropriate for the given color type
3781 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
3782 num_trans, trans_color);
3784 trans_alpha - array of alpha (transparency)
3785 entries for palette (PNG_INFO_tRNS)
3787 num_trans - number of transparent entries
3790 trans_color - graylevel or color sample values
3791 (in order red, green, blue) of the
3792 single transparent color for
3793 non-paletted images (PNG_INFO_tRNS)
3795 png_set_hIST(png_ptr, info_ptr, hist);
3797 hist - histogram of palette (array of
3798 png_uint_16) (PNG_INFO_hIST)
3800 png_set_tIME(png_ptr, info_ptr, mod_time);
3802 mod_time - time image was last modified
3805 png_set_bKGD(png_ptr, info_ptr, background);
3807 background - background color (of type
3808 png_color_16p) (PNG_VALID_bKGD)
3810 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
3812 text_ptr - array of png_text holding image
3815 text_ptr[i].compression - type of compression used
3816 on "text" PNG_TEXT_COMPRESSION_NONE
3817 PNG_TEXT_COMPRESSION_zTXt
3818 PNG_ITXT_COMPRESSION_NONE
3819 PNG_ITXT_COMPRESSION_zTXt
3820 text_ptr[i].key - keyword for comment. Must contain
3822 text_ptr[i].text - text comments for current
3823 keyword. Can be NULL or empty.
3824 text_ptr[i].text_length - length of text string,
3825 after decompression, 0 for iTXt
3826 text_ptr[i].itxt_length - length of itxt string,
3827 after decompression, 0 for tEXt/zTXt
3828 text_ptr[i].lang - language of comment (NULL or
3830 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
3831 or empty for unknown).
3833 Note that the itxt_length, lang, and lang_key
3834 members of the text_ptr structure only exist when the
3835 library is built with iTXt chunk support. Prior to
3836 libpng-1.4.0 the library was built by default without
3837 iTXt support. Also note that when iTXt is supported,
3838 they contain NULL pointers when the "compression"
3839 field contains PNG_TEXT_COMPRESSION_NONE or
3840 PNG_TEXT_COMPRESSION_zTXt.
3842 num_text - number of comments
3844 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
3847 palette_ptr - array of png_sPLT_struct structures
3848 to be added to the list of palettes
3849 in the info structure.
3850 num_spalettes - number of palette structures to be
3853 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
3856 offset_x - positive offset from the left
3859 offset_y - positive offset from the top
3862 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
3864 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
3867 res_x - pixels/unit physical resolution
3870 res_y - pixels/unit physical resolution
3873 unit_type - PNG_RESOLUTION_UNKNOWN,
3874 PNG_RESOLUTION_METER
3876 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
3878 unit - physical scale units (an integer)
3880 width - width of a pixel in physical scale units
3882 height - height of a pixel in physical scale units
3883 (width and height are doubles)
3885 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
3887 unit - physical scale units (an integer)
3889 width - width of a pixel in physical scale units
3890 expressed as a string
3892 height - height of a pixel in physical scale units
3893 (width and height are strings like "2.54")
3895 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
3898 unknowns - array of png_unknown_chunk
3899 structures holding unknown chunks
3900 unknowns[i].name - name of unknown chunk
3901 unknowns[i].data - data of unknown chunk
3902 unknowns[i].size - size of unknown chunk's data
3903 unknowns[i].location - position to write chunk in file
3904 0: do not write chunk
3905 PNG_HAVE_IHDR: before PLTE
3906 PNG_HAVE_PLTE: before IDAT
3907 PNG_AFTER_IDAT: after IDAT
3909 The "location" member is set automatically according to
3910 what part of the output file has already been written.
3911 You can change its value after calling png_set_unknown_chunks()
3912 as demonstrated in pngtest.c. Within each of the "locations",
3913 the chunks are sequenced according to their position in the
3914 structure (that is, the value of "i", which is the order in which
3915 the chunk was either read from the input file or defined with
3916 png_set_unknown_chunks).
3918 A quick word about text and num_text. text is an array of png_text
3919 structures. num_text is the number of valid structures in the array.
3920 Each png_text structure holds a language code, a keyword, a text value,
3921 and a compression type.
3923 The compression types have the same valid numbers as the compression
3924 types of the image data. Currently, the only valid number is zero.
3925 However, you can store text either compressed or uncompressed, unlike
3926 images, which always have to be compressed. So if you don't want the
3927 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
3928 Because tEXt and zTXt chunks don't have a language field, if you
3929 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
3930 any language code or translated keyword will not be written out.
3932 Until text gets around a few hundred bytes, it is not worth compressing it.
3933 After the text has been written out to the file, the compression type
3934 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
3935 so that it isn't written out again at the end (in case you are calling
3936 png_write_end() with the same struct).
3938 The keywords that are given in the PNG Specification are:
3940 Title Short (one line) title or
3943 Author Name of image's creator
3945 Description Description of image (possibly long)
3947 Copyright Copyright notice
3949 Creation Time Time of original image creation
3950 (usually RFC 1123 format, see below)
3952 Software Software used to create the image
3954 Disclaimer Legal disclaimer
3956 Warning Warning of nature of content
3958 Source Device used to create the image
3960 Comment Miscellaneous comment; conversion
3961 from other image format
3963 The keyword-text pairs work like this. Keywords should be short
3964 simple descriptions of what the comment is about. Some typical
3965 keywords are found in the PNG specification, as is some recommendations
3966 on keywords. You can repeat keywords in a file. You can even write
3967 some text before the image and some after. For example, you may want
3968 to put a description of the image before the image, but leave the
3969 disclaimer until after, so viewers working over modem connections
3970 don't have to wait for the disclaimer to go over the modem before
3971 they start seeing the image. Finally, keywords should be full
3972 words, not abbreviations. Keywords and text are in the ISO 8859-1
3973 (Latin-1) character set (a superset of regular ASCII) and can not
3974 contain NUL characters, and should not contain control or other
3975 unprintable characters. To make the comments widely readable, stick
3976 with basic ASCII, and avoid machine specific character set extensions
3977 like the IBM-PC character set. The keyword must be present, but
3978 you can leave off the text string on non-compressed pairs.
3979 Compressed pairs must have a text string, as only the text string
3980 is compressed anyway, so the compression would be meaningless.
3982 PNG supports modification time via the png_time structure. Two
3983 conversion routines are provided, png_convert_from_time_t() for
3984 time_t and png_convert_from_struct_tm() for struct tm. The
3985 time_t routine uses gmtime(). You don't have to use either of
3986 these, but if you wish to fill in the png_time structure directly,
3987 you should provide the time in universal time (GMT) if possible
3988 instead of your local time. Note that the year number is the full
3989 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
3990 that months start with 1.
3992 If you want to store the time of the original image creation, you should
3993 use a plain tEXt chunk with the "Creation Time" keyword. This is
3994 necessary because the "creation time" of a PNG image is somewhat vague,
3995 depending on whether you mean the PNG file, the time the image was
3996 created in a non-PNG format, a still photo from which the image was
3997 scanned, or possibly the subject matter itself. In order to facilitate
3998 machine-readable dates, it is recommended that the "Creation Time"
3999 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
4000 although this isn't a requirement. Unlike the tIME chunk, the
4001 "Creation Time" tEXt chunk is not expected to be automatically changed
4002 by the software. To facilitate the use of RFC 1123 dates, a function
4003 png_convert_to_rfc1123(png_timep) is provided to convert from PNG
4004 time to an RFC 1123 format string.
4006 .SS Writing unknown chunks
4008 You can use the png_set_unknown_chunks function to queue up chunks
4009 for writing. You give it a chunk name, raw data, and a size; that's
4010 all there is to it. The chunks will be written by the next following
4011 png_write_info_before_PLTE, png_write_info, or png_write_end function.
4012 Any chunks previously read into the info structure's unknown-chunk
4013 list will also be written out in a sequence that satisfies the PNG
4014 specification's ordering rules.
4016 .SS The high-level write interface
4018 At this point there are two ways to proceed; through the high-level
4019 write interface, or through a sequence of low-level write operations.
4020 You can use the high-level interface if your image data is present
4021 in the info structure. All defined output
4022 transformations are permitted, enabled by the following masks.
4024 PNG_TRANSFORM_IDENTITY No transformation
4025 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
4026 PNG_TRANSFORM_PACKSWAP Change order of packed
4028 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
4029 PNG_TRANSFORM_SHIFT Normalize pixels to the
4031 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
4033 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
4035 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
4037 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
4038 PNG_TRANSFORM_STRIP_FILLER Strip out filler
4040 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
4042 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
4045 If you have valid image data in the info structure (you can use
4046 png_set_rows() to put image data in the info structure), simply do this:
4048 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
4050 where png_transforms is an integer containing the bitwise OR of some set of
4051 transformation flags. This call is equivalent to png_write_info(),
4052 followed the set of transformations indicated by the transform mask,
4053 then png_write_image(), and finally png_write_end().
4055 (The final parameter of this call is not yet used. Someday it might point
4056 to transformation parameters required by some future output transform.)
4058 You must use png_transforms and not call any png_set_transform() functions
4059 when you use png_write_png().
4061 .SS The low-level write interface
4063 If you are going the low-level route instead, you are now ready to
4064 write all the file information up to the actual image data. You do
4065 this with a call to png_write_info().
4067 png_write_info(png_ptr, info_ptr);
4069 Note that there is one transformation you may need to do before
4070 png_write_info(). In PNG files, the alpha channel in an image is the
4071 level of opacity. If your data is supplied as a level of transparency,
4072 you can invert the alpha channel before you write it, so that 0 is
4073 fully transparent and 255 (in 8-bit or paletted images) or 65535
4074 (in 16-bit images) is fully opaque, with
4076 png_set_invert_alpha(png_ptr);
4078 This must appear before png_write_info() instead of later with the
4079 other transformations because in the case of paletted images the tRNS
4080 chunk data has to be inverted before the tRNS chunk is written. If
4081 your image is not a paletted image, the tRNS data (which in such cases
4082 represents a single color to be rendered as transparent) won't need to
4083 be changed, and you can safely do this transformation after your
4084 png_write_info() call.
4086 If you need to write a private chunk that you want to appear before
4087 the PLTE chunk when PLTE is present, you can write the PNG info in
4088 two steps, and insert code to write your own chunk between them:
4090 png_write_info_before_PLTE(png_ptr, info_ptr);
4091 png_set_unknown_chunks(png_ptr, info_ptr, ...);
4092 png_write_info(png_ptr, info_ptr);
4094 After you've written the file information, you can set up the library
4095 to handle any special transformations of the image data. The various
4096 ways to transform the data will be described in the order that they
4097 should occur. This is important, as some of these change the color
4098 type and/or bit depth of the data, and some others only work on
4099 certain color types and bit depths. Even though each transformation
4100 checks to see if it has data that it can do something with, you should
4101 make sure to only enable a transformation if it will be valid for the
4102 data. For example, don't swap red and blue on grayscale data.
4104 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
4105 the library to strip input data that has 4 or 8 bytes per pixel down
4106 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
4109 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
4111 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
4112 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
4113 is stored XRGB or RGBX.
4115 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
4116 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
4117 If the data is supplied at 1 pixel per byte, use this code, which will
4118 correctly pack the pixels into a single byte:
4120 png_set_packing(png_ptr);
4122 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
4123 data is of another bit depth, you can write an sBIT chunk into the
4124 file so that decoders can recover the original data if desired.
4126 /* Set the true bit depth of the image data */
4127 if (color_type & PNG_COLOR_MASK_COLOR)
4129 sig_bit.red = true_bit_depth;
4130 sig_bit.green = true_bit_depth;
4131 sig_bit.blue = true_bit_depth;
4136 sig_bit.gray = true_bit_depth;
4139 if (color_type & PNG_COLOR_MASK_ALPHA)
4141 sig_bit.alpha = true_bit_depth;
4144 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
4146 If the data is stored in the row buffer in a bit depth other than
4147 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
4148 this will scale the values to appear to be the correct bit depth as
4151 png_set_shift(png_ptr, &sig_bit);
4153 PNG files store 16-bit pixels in network byte order (big-endian,
4154 ie. most significant bits first). This code would be used if they are
4155 supplied the other way (little-endian, i.e. least significant bits
4156 first, the way PCs store them):
4159 png_set_swap(png_ptr);
4161 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
4162 need to change the order the pixels are packed into bytes, you can use:
4165 png_set_packswap(png_ptr);
4167 PNG files store 3 color pixels in red, green, blue order. This code
4168 would be used if they are supplied as blue, green, red:
4170 png_set_bgr(png_ptr);
4172 PNG files describe monochrome as black being zero and white being
4173 one. This code would be used if the pixels are supplied with this reversed
4174 (black being one and white being zero):
4176 png_set_invert_mono(png_ptr);
4178 Finally, you can write your own transformation function if none of
4179 the existing ones meets your needs. This is done by setting a callback
4182 png_set_write_user_transform_fn(png_ptr,
4183 write_transform_fn);
4185 You must supply the function
4187 void write_transform_fn(png_structp png_ptr, png_row_infop
4188 row_info, png_bytep data)
4190 See pngtest.c for a working example. Your function will be called
4191 before any of the other transformations are processed. If supported
4192 libpng also supplies an information routine that may be called from
4195 png_get_current_row_number(png_ptr);
4196 png_get_current_pass_number(png_ptr);
4198 This returns the current row passed to the transform. With interlaced
4199 images the value returned is the row in the input sub-image image. Use
4200 PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
4201 find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
4203 The discussion of interlace handling above contains more information on how to
4206 You can also set up a pointer to a user structure for use by your
4209 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
4211 The user_channels and user_depth parameters of this function are ignored
4212 when writing; you can set them to zero as shown.
4214 You can retrieve the pointer via the function png_get_user_transform_ptr().
4217 voidp write_user_transform_ptr =
4218 png_get_user_transform_ptr(png_ptr);
4220 It is possible to have libpng flush any pending output, either manually,
4221 or automatically after a certain number of lines have been written. To
4222 flush the output stream a single time call:
4224 png_write_flush(png_ptr);
4226 and to have libpng flush the output stream periodically after a certain
4227 number of scanlines have been written, call:
4229 png_set_flush(png_ptr, nrows);
4231 Note that the distance between rows is from the last time png_write_flush()
4232 was called, or the first row of the image if it has never been called.
4233 So if you write 50 lines, and then png_set_flush 25, it will flush the
4234 output on the next scanline, and every 25 lines thereafter, unless
4235 png_write_flush() is called before 25 more lines have been written.
4236 If nrows is too small (less than about 10 lines for a 640 pixel wide
4237 RGB image) the image compression may decrease noticeably (although this
4238 may be acceptable for real-time applications). Infrequent flushing will
4239 only degrade the compression performance by a few percent over images
4240 that do not use flushing.
4242 .SS Writing the image data
4244 That's it for the transformations. Now you can write the image data.
4245 The simplest way to do this is in one function call. If you have the
4246 whole image in memory, you can just call png_write_image() and libpng
4247 will write the image. You will need to pass in an array of pointers to
4248 each row. This function automatically handles interlacing, so you don't
4249 need to call png_set_interlace_handling() or call this function multiple
4250 times, or any of that other stuff necessary with png_write_rows().
4252 png_write_image(png_ptr, row_pointers);
4254 where row_pointers is:
4256 png_byte *row_pointers[height];
4258 You can point to void or char or whatever you use for pixels.
4260 If you don't want to write the whole image at once, you can
4261 use png_write_rows() instead. If the file is not interlaced,
4264 png_write_rows(png_ptr, row_pointers,
4267 row_pointers is the same as in the png_write_image() call.
4269 If you are just writing one row at a time, you can do this with
4270 a single row_pointer instead of an array of row_pointers:
4272 png_bytep row_pointer = row;
4274 png_write_row(png_ptr, row_pointer);
4276 When the file is interlaced, things can get a good deal more complicated.
4277 The only currently (as of the PNG Specification version 1.2, dated July
4278 1999) defined interlacing scheme for PNG files is the "Adam7" interlace
4279 scheme, that breaks down an image into seven smaller images of varying
4280 size. libpng will build these images for you, or you can do them
4281 yourself. If you want to build them yourself, see the PNG specification
4282 for details of which pixels to write when.
4284 If you don't want libpng to handle the interlacing details, just
4285 use png_set_interlace_handling() and call png_write_rows() the
4286 correct number of times to write all the sub-images
4287 (png_set_interlace_handling() returns the number of sub-images.)
4289 If you want libpng to build the sub-images, call this before you start
4292 number_of_passes = png_set_interlace_handling(png_ptr);
4294 This will return the number of passes needed. Currently, this is seven,
4295 but may change if another interlace type is added.
4297 Then write the complete image number_of_passes times.
4299 png_write_rows(png_ptr, row_pointers, number_of_rows);
4301 Think carefully before you write an interlaced image. Typically code that
4302 reads such images reads all the image data into memory, uncompressed, before
4303 doing any processing. Only code that can display an image on the fly can
4304 take advantage of the interlacing and even then the image has to be exactly
4305 the correct size for the output device, because scaling an image requires
4306 adjacent pixels and these are not available until all the passes have been
4309 If you do write an interlaced image you will hardly ever need to handle
4310 the interlacing yourself. Call png_set_interlace_handling() and use the
4311 approach described above.
4313 The only time it is conceivable that you will really need to write an
4314 interlaced image pass-by-pass is when you have read one pass by pass and
4315 made some pixel-by-pixel transformation to it, as described in the read
4316 code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
4317 to determine the size of each sub-image in turn and simply write the rows
4318 you obtained from the read code.
4320 .SS Finishing a sequential write
4322 After you are finished writing the image, you should finish writing
4323 the file. If you are interested in writing comments or time, you should
4324 pass an appropriately filled png_info pointer. If you are not interested,
4327 png_write_end(png_ptr, info_ptr);
4329 When you are done, you can free all memory used by libpng like this:
4331 png_destroy_write_struct(&png_ptr, &info_ptr);
4333 It is also possible to individually free the info_ptr members that
4334 point to libpng-allocated storage with the following function:
4336 png_free_data(png_ptr, info_ptr, mask, seq)
4338 mask - identifies data to be freed, a mask
4339 containing the bitwise OR of one or
4341 PNG_FREE_PLTE, PNG_FREE_TRNS,
4342 PNG_FREE_HIST, PNG_FREE_ICCP,
4343 PNG_FREE_PCAL, PNG_FREE_ROWS,
4344 PNG_FREE_SCAL, PNG_FREE_SPLT,
4345 PNG_FREE_TEXT, PNG_FREE_UNKN,
4346 or simply PNG_FREE_ALL
4348 seq - sequence number of item to be freed
4351 This function may be safely called when the relevant storage has
4352 already been freed, or has not yet been allocated, or was allocated
4353 by the user and not by libpng, and will in those cases do nothing.
4354 The "seq" parameter is ignored if only one item of the selected data
4355 type, such as PLTE, is allowed. If "seq" is not -1, and multiple items
4356 are allowed for the data type identified in the mask, such as text or
4357 sPLT, only the n'th item in the structure is freed, where n is "seq".
4359 If you allocated data such as a palette that you passed in to libpng
4360 with png_set_*, you must not free it until just before the call to
4361 png_destroy_write_struct().
4363 The default behavior is only to free data that was allocated internally
4364 by libpng. This can be changed, so that libpng will not free the data,
4365 or so that it will free data that was allocated by the user with png_malloc()
4366 or png_zalloc() and passed in via a png_set_*() function, with
4368 png_data_freer(png_ptr, info_ptr, freer, mask)
4371 PNG_DESTROY_WILL_FREE_DATA
4372 PNG_SET_WILL_FREE_DATA
4373 PNG_USER_WILL_FREE_DATA
4375 mask - which data elements are affected
4376 same choices as in png_free_data()
4378 For example, to transfer responsibility for some data from a read structure
4379 to a write structure, you could use
4381 png_data_freer(read_ptr, read_info_ptr,
4382 PNG_USER_WILL_FREE_DATA,
4383 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
4385 png_data_freer(write_ptr, write_info_ptr,
4386 PNG_DESTROY_WILL_FREE_DATA,
4387 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
4389 thereby briefly reassigning responsibility for freeing to the user but
4390 immediately afterwards reassigning it once more to the write_destroy
4391 function. Having done this, it would then be safe to destroy the read
4392 structure and continue to use the PLTE, tRNS, and hIST data in the write
4395 This function only affects data that has already been allocated.
4396 You can call this function before calling after the png_set_*() functions
4397 to control whether the user or png_destroy_*() is supposed to free the data.
4398 When the user assumes responsibility for libpng-allocated data, the
4399 application must use
4400 png_free() to free it, and when the user transfers responsibility to libpng
4401 for data that the user has allocated, the user must have used png_malloc()
4402 or png_zalloc() to allocate it.
4404 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
4405 separately, do not transfer responsibility for freeing text_ptr to libpng,
4406 because when libpng fills a png_text structure it combines these members with
4407 the key member, and png_free_data() will free only text_ptr.key. Similarly,
4408 if you transfer responsibility for free'ing text_ptr from libpng to your
4409 application, your application must not separately free those members.
4410 For a more compact example of writing a PNG image, see the file example.c.
4412 .SH V. Modifying/Customizing libpng:
4414 There are two issues here. The first is changing how libpng does
4415 standard things like memory allocation, input/output, and error handling.
4416 The second deals with more complicated things like adding new chunks,
4417 adding new transformations, and generally changing how libpng works.
4418 Both of those are compile-time issues; that is, they are generally
4419 determined at the time the code is written, and there is rarely a need
4420 to provide the user with a means of changing them.
4422 Memory allocation, input/output, and error handling
4424 All of the memory allocation, input/output, and error handling in libpng
4425 goes through callbacks that are user-settable. The default routines are
4426 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
4427 these functions, call the appropriate png_set_*_fn() function.
4429 Memory allocation is done through the functions png_malloc(), png_calloc(),
4430 and png_free(). These currently just call the standard C functions.
4431 png_calloc() calls png_malloc() and then clears the newly
4432 allocated memory to zero. There is limited support for certain systems
4433 with segmented memory architectures and the types of pointers declared by
4434 png.h match this; you will have to use appropriate pointers in your
4435 application. Since it is
4436 unlikely that the method of handling memory allocation on a platform
4437 will change between applications, these functions must be modified in
4438 the library at compile time. If you prefer to use a different method
4439 of allocating and freeing data, you can use png_create_read_struct_2() or
4440 png_create_write_struct_2() to register your own functions as described
4441 above. These functions also provide a void pointer that can be retrieved
4444 mem_ptr=png_get_mem_ptr(png_ptr);
4446 Your replacement memory functions must have prototypes as follows:
4448 png_voidp malloc_fn(png_structp png_ptr,
4449 png_alloc_size_t size);
4451 void free_fn(png_structp png_ptr, png_voidp ptr);
4453 Your malloc_fn() must return NULL in case of failure. The png_malloc()
4454 function will normally call png_error() if it receives a NULL from the
4455 system memory allocator or from your replacement malloc_fn().
4457 Your free_fn() will never be called with a NULL ptr, since libpng's
4458 png_free() checks for NULL before calling free_fn().
4460 Input/Output in libpng is done through png_read() and png_write(),
4461 which currently just call fread() and fwrite(). The FILE * is stored in
4462 png_struct and is initialized via png_init_io(). If you wish to change
4463 the method of I/O, the library supplies callbacks that you can set
4464 through the function png_set_read_fn() and png_set_write_fn() at run
4465 time, instead of calling the png_init_io() function. These functions
4466 also provide a void pointer that can be retrieved via the function
4467 png_get_io_ptr(). For example:
4469 png_set_read_fn(png_structp read_ptr,
4470 voidp read_io_ptr, png_rw_ptr read_data_fn)
4472 png_set_write_fn(png_structp write_ptr,
4473 voidp write_io_ptr, png_rw_ptr write_data_fn,
4474 png_flush_ptr output_flush_fn);
4476 voidp read_io_ptr = png_get_io_ptr(read_ptr);
4477 voidp write_io_ptr = png_get_io_ptr(write_ptr);
4479 The replacement I/O functions must have prototypes as follows:
4481 void user_read_data(png_structp png_ptr,
4482 png_bytep data, png_size_t length);
4484 void user_write_data(png_structp png_ptr,
4485 png_bytep data, png_size_t length);
4487 void user_flush_data(png_structp png_ptr);
4489 The user_read_data() function is responsible for detecting and
4490 handling end-of-data errors.
4492 Supplying NULL for the read, write, or flush functions sets them back
4493 to using the default C stream functions, which expect the io_ptr to
4494 point to a standard *FILE structure. It is probably a mistake
4495 to use NULL for one of write_data_fn and output_flush_fn but not both
4496 of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
4497 It is an error to read from a write stream, and vice versa.
4499 Error handling in libpng is done through png_error() and png_warning().
4500 Errors handled through png_error() are fatal, meaning that png_error()
4501 should never return to its caller. Currently, this is handled via
4502 setjmp() and longjmp() (unless you have compiled libpng with
4503 PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
4504 but you could change this to do things like exit() if you should wish,
4505 as long as your function does not return.
4507 On non-fatal errors, png_warning() is called
4508 to print a warning message, and then control returns to the calling code.
4509 By default png_error() and png_warning() print a message on stderr via
4510 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
4511 (because you don't want the messages) or PNG_NO_STDIO defined (because
4512 fprintf() isn't available). If you wish to change the behavior of the error
4513 functions, you will need to set up your own message callbacks. These
4514 functions are normally supplied at the time that the png_struct is created.
4515 It is also possible to redirect errors and warnings to your own replacement
4516 functions after png_create_*_struct() has been called by calling:
4518 png_set_error_fn(png_structp png_ptr,
4519 png_voidp error_ptr, png_error_ptr error_fn,
4520 png_error_ptr warning_fn);
4522 png_voidp error_ptr = png_get_error_ptr(png_ptr);
4524 If NULL is supplied for either error_fn or warning_fn, then the libpng
4525 default function will be used, calling fprintf() and/or longjmp() if a
4526 problem is encountered. The replacement error functions should have
4527 parameters as follows:
4529 void user_error_fn(png_structp png_ptr,
4530 png_const_charp error_msg);
4532 void user_warning_fn(png_structp png_ptr,
4533 png_const_charp warning_msg);
4535 The motivation behind using setjmp() and longjmp() is the C++ throw and
4536 catch exception handling methods. This makes the code much easier to write,
4537 as there is no need to check every return code of every function call.
4538 However, there are some uncertainties about the status of local variables
4539 after a longjmp, so the user may want to be careful about doing anything
4540 after setjmp returns non-zero besides returning itself. Consult your
4541 compiler documentation for more details. For an alternative approach, you
4542 may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net),
4543 which is illustrated in pngvalid.c and in contrib/visupng.
4547 If you need to read or write custom chunks, you may need to get deeper
4548 into the libpng code. The library now has mechanisms for storing
4549 and writing chunks of unknown type; you can even declare callbacks
4550 for custom chunks. However, this may not be good enough if the
4551 library code itself needs to know about interactions between your
4552 chunk and existing `intrinsic' chunks.
4554 If you need to write a new intrinsic chunk, first read the PNG
4555 specification. Acquire a first level of understanding of how it works.
4556 Pay particular attention to the sections that describe chunk names,
4557 and look at how other chunks were designed, so you can do things
4558 similarly. Second, check out the sections of libpng that read and
4559 write chunks. Try to find a chunk that is similar to yours and use
4560 it as a template. More details can be found in the comments inside
4561 the code. It is best to handle private or unknown chunks in a generic method,
4562 via callback functions, instead of by modifying libpng functions. This
4563 is illustrated in pngtest.c, which uses a callback function to handle a
4564 private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
4567 If you wish to write your own transformation for the data, look through
4568 the part of the code that does the transformations, and check out some of
4569 the simpler ones to get an idea of how they work. Try to find a similar
4570 transformation to the one you want to add and copy off of it. More details
4571 can be found in the comments inside the code itself.
4573 .SS Configuring for 16-bit platforms
4575 You will want to look into zconf.h to tell zlib (and thus libpng) that
4576 it cannot allocate more then 64K at a time. Even if you can, the memory
4577 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
4579 .SS Configuring for DOS
4581 For DOS users who only have access to the lower 640K, you will
4582 have to limit zlib's memory usage via a png_set_compression_mem_level()
4583 call. See zlib.h or zconf.h in the zlib library for more information.
4585 .SS Configuring for Medium Model
4587 Libpng's support for medium model has been tested on most of the popular
4588 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
4589 defined, and FAR gets defined to far in pngconf.h, and you should be
4590 all set. Everything in the library (except for zlib's structure) is
4591 expecting far data. You must use the typedefs with the p or pp on
4592 the end for pointers (or at least look at them and be careful). Make
4593 note that the rows of data are defined as png_bytepp, which is
4594 an "unsigned char far * far *".
4596 .SS Configuring for gui/windowing platforms:
4598 You will need to write new error and warning functions that use the GUI
4599 interface, as described previously, and set them to be the error and
4600 warning functions at the time that png_create_*_struct() is called,
4601 in order to have them available during the structure initialization.
4602 They can be changed later via png_set_error_fn(). On some compilers,
4603 you may also have to change the memory allocators (png_malloc, etc.).
4605 .SS Configuring for compiler xxx:
4607 All includes for libpng are in pngconf.h. If you need to add, change
4608 or delete an include, this is the place to do it.
4609 The includes that are not needed outside libpng are placed in pngpriv.h,
4610 which is only used by the routines inside libpng itself.
4611 The files in libpng proper only include pngpriv.h and png.h, which
4612 %14%in turn includes pngconf.h.
4613 in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h.
4614 As of libpng-1.5.0, pngpriv.h also includes three other private header
4615 files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material
4616 that previously appeared in the public headers.
4618 .SS Configuring zlib:
4620 There are special functions to configure the compression. Perhaps the
4621 most useful one changes the compression level, which currently uses
4622 input compression values in the range 0 - 9. The library normally
4623 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
4624 have shown that for a large majority of images, compression values in
4625 the range 3-6 compress nearly as well as higher levels, and do so much
4626 faster. For online applications it may be desirable to have maximum speed
4627 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
4628 specify no compression (Z_NO_COMPRESSION = 0), but this would create
4629 files larger than just storing the raw bitmap. You can specify the
4630 compression level by calling:
4633 png_set_compression_level(png_ptr, level);
4635 Another useful one is to reduce the memory level used by the library.
4636 The memory level defaults to 8, but it can be lowered if you are
4637 short on memory (running DOS, for example, where you only have 640K).
4638 Note that the memory level does have an effect on compression; among
4639 other things, lower levels will result in sections of incompressible
4640 data being emitted in smaller stored blocks, with a correspondingly
4641 larger relative overhead of up to 15% in the worst case.
4644 png_set_compression_mem_level(png_ptr, level);
4646 The other functions are for configuring zlib. They are not recommended
4647 for normal use and may result in writing an invalid PNG file. See
4648 zlib.h for more information on what these mean.
4651 png_set_compression_strategy(png_ptr,
4654 png_set_compression_window_bits(png_ptr,
4657 png_set_compression_method(png_ptr, method);
4659 png_set_compression_buffer_size(png_ptr, size);
4661 As of libpng version 1.5.4, additional APIs became
4662 available to set these separately for non-IDAT
4663 compressed chunks such as zTXt, iTXt, and iCCP:
4666 #if PNG_LIBPNG_VER <= 10504
4667 png_set_text_compression_level(png_ptr, level);
4669 png_set_text_compression_mem_level(png_ptr, level);
4671 png_set_text_compression_strategy(png_ptr,
4674 png_set_text_compression_window_bits(png_ptr,
4677 png_set_text_compression_method(png_ptr, method);
4680 .SS Controlling row filtering
4682 If you want to control whether libpng uses filtering or not, which
4683 filters are used, and how it goes about picking row filters, you
4684 can call one of these functions. The selection and configuration
4685 of row filters can have a significant impact on the size and
4686 encoding speed and a somewhat lesser impact on the decoding speed
4687 of an image. Filtering is enabled by default for RGB and grayscale
4688 images (with and without alpha), but not for paletted images nor
4689 for any images with bit depths less than 8 bits/pixel.
4691 The 'method' parameter sets the main filtering method, which is
4692 currently only '0' in the PNG 1.2 specification. The 'filters'
4693 parameter sets which filter(s), if any, should be used for each
4694 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
4695 to turn filtering on and off, respectively.
4697 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
4698 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
4699 ORed together with '|' to specify one or more filters to use.
4700 These filters are described in more detail in the PNG specification.
4701 If you intend to change the filter type during the course of writing
4702 the image, you should start with flags set for all of the filters
4703 you intend to use so that libpng can initialize its internal
4704 structures appropriately for all of the filter types. (Note that this
4705 means the first row must always be adaptively filtered, because libpng
4706 currently does not allocate the filter buffers until png_write_row()
4707 is called for the first time.)
4709 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
4710 PNG_FILTER_UP | PNG_FILTER_AVG |
4711 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
4713 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
4715 The second parameter can also be
4716 PNG_INTRAPIXEL_DIFFERENCING if you are
4717 writing a PNG to be embedded in a MNG
4718 datastream. This parameter must be the
4719 same as the value of filter_method used
4722 It is also possible to influence how libpng chooses from among the
4723 available filters. This is done in one or both of two ways - by
4724 telling it how important it is to keep the same filter for successive
4725 rows, and by telling it the relative computational costs of the filters.
4727 double weights[3] = {1.5, 1.3, 1.1},
4728 costs[PNG_FILTER_VALUE_LAST] =
4729 {1.0, 1.3, 1.3, 1.5, 1.7};
4731 png_set_filter_heuristics(png_ptr,
4732 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
4735 The weights are multiplying factors that indicate to libpng that the
4736 row filter should be the same for successive rows unless another row filter
4737 is that many times better than the previous filter. In the above example,
4738 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
4739 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
4740 and still be chosen, while the NONE filter could have a sum 1.1 times
4741 higher than other filters and still be chosen. Unspecified weights are
4742 taken to be 1.0, and the specified weights should probably be declining
4743 like those above in order to emphasize recent filters over older filters.
4745 The filter costs specify for each filter type a relative decoding cost
4746 to be considered when selecting row filters. This means that filters
4747 with higher costs are less likely to be chosen over filters with lower
4748 costs, unless their "sum of absolute differences" is that much smaller.
4749 The costs do not necessarily reflect the exact computational speeds of
4750 the various filters, since this would unduly influence the final image
4753 Note that the numbers above were invented purely for this example and
4754 are given only to help explain the function usage. Little testing has
4755 been done to find optimum values for either the costs or the weights.
4757 .SS Removing unwanted object code
4759 There are a bunch of #define's in pngconf.h that control what parts of
4760 libpng are compiled. All the defines end in _SUPPORTED. If you are
4761 never going to use a capability, you can change the #define to #undef
4762 before recompiling libpng and save yourself code and data space, or
4763 you can turn off individual capabilities with defines that begin with
4766 In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
4768 You can also turn all of the transforms and ancillary chunk capabilities
4769 off en masse with compiler directives that define
4770 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
4772 along with directives to turn on any of the capabilities that you do
4773 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
4774 transformations but still leave the library fully capable of reading
4775 and writing PNG files with all known public chunks. Use of the
4776 PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
4777 that is incapable of reading or writing ancillary chunks. If you are
4778 not using the progressive reading capability, you can turn that off
4779 with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
4780 capability, which you'll still have).
4782 All the reading and writing specific code are in separate files, so the
4783 linker should only grab the files it needs. However, if you want to
4784 make sure, or if you are building a stand alone library, all the
4785 reading files start with "pngr" and all the writing files start with "pngw".
4786 The files that don't match either (like png.c, pngtrans.c, etc.)
4787 are used for both reading and writing, and always need to be included.
4788 The progressive reader is in pngpread.c
4790 If you are creating or distributing a dynamically linked library (a .so
4791 or DLL file), you should not remove or disable any parts of the library,
4792 as this will cause applications linked with different versions of the
4793 library to fail if they call functions not available in your library.
4794 The size of the library itself should not be an issue, because only
4795 those sections that are actually used will be loaded into memory.
4797 .SS Requesting debug printout
4799 The macro definition PNG_DEBUG can be used to request debugging
4800 printout. Set it to an integer value in the range 0 to 3. Higher
4801 numbers result in increasing amounts of debugging information. The
4802 information is printed to the "stderr" file, unless another file
4803 name is specified in the PNG_DEBUG_FILE macro definition.
4805 When PNG_DEBUG > 0, the following functions (macros) become available:
4807 png_debug(level, message)
4808 png_debug1(level, message, p1)
4809 png_debug2(level, message, p1, p2)
4811 in which "level" is compared to PNG_DEBUG to decide whether to print
4812 the message, "message" is the formatted string to be printed,
4813 and p1 and p2 are parameters that are to be embedded in the string
4814 according to printf-style formatting directives. For example,
4816 png_debug1(2, "foo=%d\n", foo);
4821 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
4823 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
4824 can still use PNG_DEBUG to control your own debugging:
4830 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
4831 having level = 0 will be printed. There aren't any such statements in
4832 this version of libpng, but if you insert some they will be printed.
4836 The MNG specification (available at http://www.libpng.org/pub/mng) allows
4837 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
4838 Libpng can support some of these extensions. To enable them, use the
4839 png_permit_mng_features() function:
4841 feature_set = png_permit_mng_features(png_ptr, mask)
4843 mask is a png_uint_32 containing the bitwise OR of the
4844 features you want to enable. These include
4845 PNG_FLAG_MNG_EMPTY_PLTE
4846 PNG_FLAG_MNG_FILTER_64
4847 PNG_ALL_MNG_FEATURES
4849 feature_set is a png_uint_32 that is the bitwise AND of
4850 your mask with the set of MNG features that is
4851 supported by the version of libpng that you are using.
4853 It is an error to use this function when reading or writing a standalone
4854 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
4855 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
4856 and the MHDR and MEND chunks. Libpng does not provide support for these
4857 or any other MNG chunks; your application must provide its own support for
4858 them. You may wish to consider using libmng (available at
4859 http://www.libmng.com) instead.
4861 .SH VII. Changes to Libpng from version 0.88
4863 It should be noted that versions of libpng later than 0.96 are not
4864 distributed by the original libpng author, Guy Schalnat, nor by
4865 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
4866 distributed versions 0.89 through 0.96, but rather by another member
4867 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
4868 still alive and well, but they have moved on to other things.
4870 The old libpng functions png_read_init(), png_write_init(),
4871 png_info_init(), png_read_destroy(), and png_write_destroy() have been
4872 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
4873 functions will be removed from libpng version 1.4.0.
4875 The preferred method of creating and initializing the libpng structures is
4876 via the png_create_read_struct(), png_create_write_struct(), and
4877 png_create_info_struct() because they isolate the size of the structures
4878 from the application, allow version error checking, and also allow the
4879 use of custom error handling routines during the initialization, which
4880 the old functions do not. The functions png_read_destroy() and
4881 png_write_destroy() do not actually free the memory that libpng
4882 allocated for these structs, but just reset the data structures, so they
4883 can be used instead of png_destroy_read_struct() and
4884 png_destroy_write_struct() if you feel there is too much system overhead
4885 allocating and freeing the png_struct for each image read.
4887 Setting the error callbacks via png_set_message_fn() before
4888 png_read_init() as was suggested in libpng-0.88 is no longer supported
4889 because this caused applications that do not use custom error functions
4890 to fail if the png_ptr was not initialized to zero. It is still possible
4891 to set the error callbacks AFTER png_read_init(), or to change them with
4892 png_set_error_fn(), which is essentially the same function, but with a new
4893 name to force compilation errors with applications that try to use the old
4896 Starting with version 1.0.7, you can find out which version of the library
4897 you are using at run-time:
4899 png_uint_32 libpng_vn = png_access_version_number();
4901 The number libpng_vn is constructed from the major version, minor
4902 version with leading zero, and release number with leading zero,
4903 (e.g., libpng_vn for version 1.0.7 is 10007).
4905 Note that this function does not take a png_ptr, so you can call it
4906 before you've created one.
4908 You can also check which version of png.h you used when compiling your
4911 png_uint_32 application_vn = PNG_LIBPNG_VER;
4913 .SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
4915 Support for user memory management was enabled by default. To
4916 accomplish this, the functions png_create_read_struct_2(),
4917 png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
4918 png_malloc_default(), and png_free_default() were added.
4920 Support for the iTXt chunk has been enabled by default as of
4923 Support for certain MNG features was enabled.
4925 Support for numbered error messages was added. However, we never got
4926 around to actually numbering the error messages. The function
4927 png_set_strip_error_numbers() was added (Note: the prototype for this
4928 function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
4929 builds of libpng-1.2.15. It was restored in libpng-1.2.36).
4931 The png_malloc_warn() function was added at libpng-1.2.3. This issues
4932 a png_warning and returns NULL instead of aborting when it fails to
4933 acquire the requested memory allocation.
4935 Support for setting user limits on image width and height was enabled
4936 by default. The functions png_set_user_limits(), png_get_user_width_max(),
4937 and png_get_user_height_max() were added at libpng-1.2.6.
4939 The png_set_add_alpha() function was added at libpng-1.2.7.
4941 The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
4942 Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
4943 tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
4946 A number of macro definitions in support of runtime selection of
4947 assembler code features (especially Intel MMX code support) were
4948 added at libpng-1.2.0:
4950 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
4951 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
4952 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
4953 PNG_ASM_FLAG_MMX_READ_INTERLACE
4954 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
4955 PNG_ASM_FLAG_MMX_READ_FILTER_UP
4956 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
4957 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
4958 PNG_ASM_FLAGS_INITIALIZED
4964 We added the following functions in support of runtime
4965 selection of assembler code features:
4967 png_get_mmx_flagmask()
4968 png_set_mmx_thresholds()
4970 png_get_mmx_bitdepth_threshold()
4971 png_get_mmx_rowbytes_threshold()
4974 We replaced all of these functions with simple stubs in libpng-1.2.20,
4975 when the Intel assembler code was removed due to a licensing issue.
4977 These macros are deprecated:
4979 PNG_READ_TRANSFORMS_NOT_SUPPORTED
4980 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
4981 PNG_NO_SEQUENTIAL_READ_SUPPORTED
4982 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
4983 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
4984 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
4986 They have been replaced, respectively, by:
4988 PNG_NO_READ_TRANSFORMS
4989 PNG_NO_PROGRESSIVE_READ
4990 PNG_NO_SEQUENTIAL_READ
4991 PNG_NO_WRITE_TRANSFORMS
4992 PNG_NO_READ_ANCILLARY_CHUNKS
4993 PNG_NO_WRITE_ANCILLARY_CHUNKS
4995 PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
4996 deprecated since libpng-1.0.16 and libpng-1.2.6.
4999 png_check_sig(sig, num)
5001 !png_sig_cmp(sig, 0, num)
5002 It has been deprecated since libpng-0.90.
5005 png_set_gray_1_2_4_to_8()
5006 which also expands tRNS to alpha was replaced with
5007 png_set_expand_gray_1_2_4_to_8()
5008 which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
5010 .SH IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
5012 Private libpng prototypes and macro definitions were moved from
5013 png.h and pngconf.h into a new pngpriv.h header file.
5015 Functions png_set_benign_errors(), png_benign_error(), and
5016 png_chunk_benign_error() were added.
5018 Support for setting the maximum amount of memory that the application
5019 will allocate for reading chunks was added, as a security measure.
5020 The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
5021 were added to the library.
5023 We implemented support for I/O states by adding png_ptr member io_state
5024 and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
5026 We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
5029 Checking for and reporting of errors in the IHDR chunk is more thorough.
5031 Support for global arrays was removed, to improve thread safety.
5033 Some obsolete/deprecated macros and functions have been removed.
5035 Typecasted NULL definitions such as
5036 #define png_voidp_NULL (png_voidp)NULL
5037 were eliminated. If you used these in your application, just use
5040 The png_struct and info_struct members "trans" and "trans_values" were
5041 changed to "trans_alpha" and "trans_color", respectively.
5043 The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
5046 The PNG_1_0_X and PNG_1_2_X macros were eliminated.
5048 The PNG_LEGACY_SUPPORTED macro was eliminated.
5050 Many WIN32_WCE #ifdefs were removed.
5052 The functions png_read_init(info_ptr), png_write_init(info_ptr),
5053 png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
5054 have been removed. They have been deprecated since libpng-0.95.
5056 The png_permit_empty_plte() was removed. It has been deprecated
5057 since libpng-1.0.9. Use png_permit_mng_features() instead.
5059 We removed the obsolete stub functions png_get_mmx_flagmask(),
5060 png_set_mmx_thresholds(), png_get_asm_flags(),
5061 png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
5062 png_set_asm_flags(), and png_mmx_supported()
5064 We removed the obsolete png_check_sig(), png_memcpy_check(), and
5065 png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),
5066 and memset(), respectively.
5068 The function png_set_gray_1_2_4_to_8() was removed. It has been
5069 deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
5070 png_set_expand_gray_1_2_4_to_8() because the former function also
5071 expanded any tRNS chunk to an alpha channel.
5073 Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
5074 were added and are used by default instead of the corresponding
5075 functions. Unfortunately,
5076 from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5077 function) incorrectly returned a value of type png_uint_32.
5079 We changed the prototype for png_malloc() from
5080 png_malloc(png_structp png_ptr, png_uint_32 size)
5082 png_malloc(png_structp png_ptr, png_alloc_size_t size)
5084 This also applies to the prototype for the user replacement malloc_fn().
5086 The png_calloc() function was added and is used in place of
5087 of "png_malloc(); memset();" except in the case in png_read_png()
5088 where the array consists of pointers; in this case a "for" loop is used
5089 after the png_malloc() to set the pointers to NULL, to give robust.
5090 behavior in case the application runs out of memory part-way through
5093 We changed the prototypes of png_get_compression_buffer_size() and
5094 png_set_compression_buffer_size() to work with png_size_t instead of
5097 Support for numbered error messages was removed by default, since we
5098 never got around to actually numbering the error messages. The function
5099 png_set_strip_error_numbers() was removed from the library by default.
5101 The png_zalloc() and png_zfree() functions are no longer exported.
5102 The png_zalloc() function no longer zeroes out the memory that it
5105 Support for dithering was disabled by default in libpng-1.4.0, because
5106 it has not been well tested and doesn't actually "dither".
5108 removed, however, and could be enabled by building libpng with
5109 PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
5110 was reenabled, but the function was renamed png_set_quantize() to
5111 reflect more accurately what it actually does. At the same time,
5112 the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
5113 PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
5114 was renamed to PNG_READ_QUANTIZE_SUPPORTED.
5116 We removed the trailing '.' from the warning and error messages.
5118 .SH X. Changes to Libpng from version 1.4.x to 1.5.x
5120 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5121 function) incorrectly returned a value of type png_uint_32.
5123 A. Changes that affect users of libpng
5125 There are no substantial API changes between the non-deprecated parts of
5126 the 1.4.5 API and the 1.5.0 API, however the ability to directly access
5127 the main libpng control structures, png_struct and png_info, deprecated
5128 in earlier versions of libpng, has been completely removed from
5131 We no longer include zlib.h in png.h. Applications that need access
5132 to information in zlib.h will need to add the '#include "zlib.h"'
5133 directive. It does not matter whether it is placed prior to or after
5134 the '"#include png.h"' directive.
5136 We moved the png_strcpy(), png_strncpy(), png_strlen(), png_memcpy(),
5137 png_memcmp(), png_sprintf, and png_memcpy() macros into a private
5138 header file (pngpriv.h) that is not accessible to applications.
5140 In png_get_iCCP, the type of "profile" was changed from png_charpp
5141 to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
5143 There are changes of form in png.h, including new and changed macros to
5144 declare parts of the API. Some API functions with arguments that are
5145 pointers to data not modified within the function have been corrected to
5146 declare these arguments with PNG_CONST.
5148 Much of the internal use of C macros to control the library build has also
5149 changed and some of this is visible in the exported header files, in
5150 particular the use of macros to control data and API elements visible
5151 during application compilation may require significant revision to
5152 application code. (It is extremely rare for an application to do this.)
5154 Any program that compiled against libpng 1.4 and did not use deprecated
5155 features or access internal library structures should compile and work
5156 against libpng 1.5, except for the change in the prototype for
5157 png_get_iCCP() and png_set_iCCP() API functions mentioned above.
5159 libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
5160 interlaced images. The macros return the number of rows and columns in
5161 each pass and information that can be used to de-interlace and (if
5162 absolutely necessary) interlace an image.
5164 libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
5165 the application-provided png_longjmp_ptr on the internal, but application
5166 initialized, longjmp buffer. It is provided as a convenience to avoid
5167 the need to use the png_jmpbuf macro, which had the unnecessary side
5168 effect of resetting the internal png_longjmp_ptr value.
5170 libpng 1.5.0 includes a complete fixed point API. By default this is
5171 present along with the corresponding floating point API. In general the
5172 fixed point API is faster and smaller than the floating point one because
5173 the PNG file format used fixed point, not floating point. This applies
5174 even if the library uses floating point in internal calculations. A new
5175 macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
5176 uses floating point arithmetic (the default) or fixed point arithmetic
5177 internally for performance critical calculations such as gamma correction.
5178 In some cases, the gamma calculations may produce slightly different
5179 results. This has changed the results in png_rgb_to_gray and in alpha
5180 composition (png_set_background for example). This applies even if the
5181 original image was already linear (gamma == 1.0) and, therefore, it is
5182 not necessary to linearize the image. This is because libpng has *not*
5183 been changed to optimize that case correctly, yet.
5185 Fixed point support for the sCAL chunk comes with an important caveat;
5186 the sCAL specification uses a decimal encoding of floating point values
5187 and the accuracy of PNG fixed point values is insufficient for
5188 representation of these values. Consequently a "string" API
5189 (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
5190 arbitrary sCAL chunks in the absence of either the floating point API or
5191 internal floating point calculations.
5193 Applications no longer need to include the optional distribution header
5194 file pngusr.h or define the corresponding macros during application
5195 build in order to see the correct variant of the libpng API. From 1.5.0
5196 application code can check for the corresponding _SUPPORTED macro:
5198 #ifdef PNG_INCH_CONVERSIONS_SUPPORTED
5199 /* code that uses the inch conversion APIs. */
5202 This macro will only be defined if the inch conversion functions have been
5203 compiled into libpng. The full set of macros, and whether or not support
5204 has been compiled in, are available in the header file pnglibconf.h.
5205 This header file is specific to the libpng build. Notice that prior to
5206 1.5.0 the _SUPPORTED macros would always have the default definition unless
5207 reset by pngusr.h or by explicit settings on the compiler command line.
5208 These settings may produce compiler warnings or errors in 1.5.0 because
5209 of macro redefinition.
5211 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5212 function) incorrectly returned a value of type png_uint_32. libpng 1.5.0
5213 is consistent with the implementation in 1.4.5 and 1.2.x (where the macro
5216 Applications can now choose whether to use these macros or to call the
5217 corresponding function by defining PNG_USE_READ_MACROS or
5218 PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
5219 only supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0
5220 will lead to a link failure.
5222 Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
5223 when compressing the IDAT data and textual data such as zTXt and iCCP.
5224 In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
5225 We added five png_set_text_*() functions for setting the parameters to
5226 use with textual data.
5228 Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
5229 option was off by default, and slightly inaccurate scaling occurred.
5230 This option can no longer be turned off, and the choice of accurate
5231 or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
5232 API for accurate scaling or the old png_set_strip_16_to_8() API for simple
5235 Prior to libpng-1.5.4, the png_set_user_limits() function could only be
5236 used to reduce the width and height limits from the value of
5237 PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
5238 that it could be used to override them. Now this function will reduce or
5239 increase the limits.
5241 B. Changes to the build and configuration of libpng
5243 Details of internal changes to the library code can be found in the CHANGES
5244 file and in the GIT repository logs. These will be of no concern to the vast
5245 majority of library users or builders, however the few who configure libpng
5246 to a non-default feature set may need to change how this is done.
5248 There should be no need for library builders to alter build scripts if
5249 these use the distributed build support - configure or the makefiles -
5250 however users of the makefiles may care to update their build scripts
5251 to build pnglibconf.h where the corresponding makefile does not do so.
5253 Building libpng with a non-default configuration has changed completely.
5254 The old method using pngusr.h should still work correctly even though the
5255 way pngusr.h is used in the build has been changed; however, library
5256 builders will probably want to examine the changes to take advantage of
5257 new capabilities and to simplify their build system.
5259 B.1 Specific changes to library configuration capabilities
5261 The library now supports a complete fixed point implementation and can
5262 thus be used on systems that have no floating point support or very
5263 limited or slow support. Previously gamma correction, an essential part
5264 of complete PNG support, required reasonably fast floating point.
5266 As part of this the choice of internal implementation has been made
5267 independent of the choice of fixed versus floating point APIs and all the
5268 missing fixed point APIs have been implemented.
5270 The exact mechanism used to control attributes of API functions has
5271 changed. A single set of operating system independent macro definitions
5272 is used and operating system specific directives are defined in
5275 As part of this the mechanism used to choose procedure call standards on
5276 those systems that allow a choice has been changed. At present this only
5277 affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems
5278 running on Intel processors. As before, PNGAPI is defined where required
5279 to control the exported API functions; however, two new macros, PNGCBAPI
5280 and PNGCAPI, are used instead for callback functions (PNGCBAPI) and
5281 (PNGCAPI) for functions that must match a C library prototype (currently
5282 only png_longjmp_ptr, which must match the C longjmp function.) The new
5283 approach is documented in pngconf.h
5285 Despite these changes, libpng 1.5.0 only supports the native C function
5286 calling standard on those platforms tested so far (__cdecl on Microsoft
5287 Windows). This is because the support requirements for alternative
5288 calling conventions seem to no longer exist. Developers who find it
5289 necessary to set PNG_API_RULE to 1 should advise the mailing list
5290 (png-mng-implement) of this and library builders who use Openwatcom and
5291 therefore set PNG_API_RULE to 2 should also contact the mailing list.
5293 A new test program, pngvalid, is provided in addition to pngtest.
5294 pngvalid validates the arithmetic accuracy of the gamma correction
5295 calculations and includes a number of validations of the file format.
5296 A subset of the full range of tests is run when "make check" is done
5297 (in the 'configure' build.) pngvalid also allows total allocated memory
5298 usage to be evaluated and performs additional memory overwrite validation.
5300 Many changes to individual feature macros have been made. The following
5301 are the changes most likely to be noticed by library builders who
5304 1) All feature macros now have consistent naming:
5306 #define PNG_NO_feature turns the feature off
5307 #define PNG_feature_SUPPORTED turns the feature on
5309 pnglibconf.h contains one line for each feature macro which is either:
5311 #define PNG_feature_SUPPORTED
5313 if the feature is supported or:
5315 /*#undef PNG_feature_SUPPORTED*/
5317 if it is not. Library code consistently checks for the 'SUPPORTED' macro.
5318 It does not, and libpng applications should not, check for the 'NO' macro
5319 which will not normally be defined even if the feature is not supported.
5320 The 'NO' macros are only used internally for setting or not setting the
5321 corresponding 'SUPPORTED' macros.
5323 Compatibility with the old names is provided as follows:
5325 PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
5327 And the following definitions disable the corresponding feature:
5329 PNG_SETJMP_NOT_SUPPORTED disables SETJMP
5330 PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
5331 PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
5332 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
5333 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
5334 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
5336 Library builders should remove use of the above, inconsistent, names.
5338 2) Warning and error message formatting was previously conditional on
5339 the STDIO feature. The library has been changed to use the
5340 CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
5341 the library no longer uses the printf(3) functions, even though the
5342 default read/write implementations use (FILE) style stdio.h functions.
5344 3) Three feature macros now control the fixed/floating point decisions:
5346 PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
5348 PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
5349 practice these are normally required internally anyway (because the PNG
5350 file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
5351 merely stops the function from being exported.
5353 PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
5354 point implementation or the fixed point one. Typically the fixed point
5355 implementation is larger and slower than the floating point implementation
5356 on a system that supports floating point, however it may be faster on a
5357 system which lacks floating point hardware and therefore uses a software
5360 4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
5361 functions to read and write ints to be disabled independently of
5362 PNG_USE_READ_MACROS, which allows libpng to be built with the functions
5363 even though the default is to use the macros - this allows applications
5364 to choose at app buildtime whether or not to use macros (previously
5365 impossible because the functions weren't in the default build.)
5367 B.2 Changes to the configuration mechanism
5369 Prior to libpng-1.5.0 library builders who needed to configure libpng
5370 had either to modify the exported pngconf.h header file to add system
5371 specific configuration or had to write feature selection macros into
5372 pngusr.h and cause this to be included into pngconf.h by defining
5373 PNG_USER_CONFIG. The latter mechanism had the disadvantage that an
5374 application built without PNG_USER_CONFIG defined would see the
5375 unmodified, default, libpng API and thus would probably fail to link.
5377 These mechanisms still work in the configure build and in any makefile
5378 build that builds pnglibconf.h, although the feature selection macros
5379 have changed somewhat as described above. In 1.5.0, however, pngusr.h is
5380 processed only once, when the exported header file pnglibconf.h is built.
5381 pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the
5382 build of pnglibconf.h and it is never included in an application build.
5384 The rarely used alternative of adding a list of feature macros to the
5385 CFLAGS setting in the build also still works, however the macros will be
5386 copied to pnglibconf.h and this may produce macro redefinition warnings
5387 when the individual C files are compiled.
5389 All configuration now only works if pnglibconf.h is built from
5390 scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan
5391 (the original author of awk) maintains C source code of that awk and this
5392 and all known later implementations (often called by subtly different
5393 names - nawk and gawk for example) are adequate to build pnglibconf.h.
5394 The Sun Microsystems (now Oracle) program 'awk' is an earlier version
5395 and does not work; this may also apply to other systems that have a
5396 functioning awk called 'nawk'.
5398 Configuration options are now documented in scripts/pnglibconf.dfa. This
5399 file also includes dependency information that ensures a configuration is
5400 consistent; that is, if a feature is switched off dependent features are
5401 also removed. As a recommended alternative to using feature macros in
5402 pngusr.h a system builder may also define equivalent options in pngusr.dfa
5403 (or, indeed, any file) and add that to the configuration by setting
5404 DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate
5405 how to do this, and a case where pngusr.h is still required.
5407 .SH XI. Detecting libpng
5409 The png_get_io_ptr() function has been present since libpng-0.88, has never
5410 changed, and is unaffected by conditional compilation macros. It is the
5411 best choice for use in configure scripts for detecting the presence of any
5412 libpng version since 0.88. In an autoconf "configure.in" you could use
5414 AC_CHECK_LIB(png, png_get_io_ptr, ...
5416 .SH XII. Source code repository
5418 Since about February 2009, version 1.2.34, libpng has been under "git" source
5419 control. The git repository was built from old libpng-x.y.z.tar.gz files
5420 going back to version 0.70. You can access the git repository (read only)
5423 git://libpng.git.sourceforge.net/gitroot/libpng
5425 or you can browse it via "gitweb" at
5427 http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
5429 Patches can be sent to glennrp at users.sourceforge.net or to
5430 png-mng-implement at lists.sourceforge.net or you can upload them to
5431 the libpng bug tracker at
5433 http://libpng.sourceforge.net
5435 We also accept patches built from the tar or zip distributions, and
5436 simple verbal discriptions of bug fixes, reported either to the
5437 SourceForge bug tracker, to the png-mng-implement at lists.sf.net
5438 mailing list, or directly to glennrp.
5440 .SH XIII. Coding style
5442 Our coding style is similar to the "Allman" style, with curly
5443 braces on separate lines:
5450 else if (another condition)
5455 The braces can be omitted from simple one-line actions:
5460 We use 3-space indentation, except for continued statements which
5461 are usually indented the same as the first line of the statement
5462 plus four more spaces.
5464 For macro definitions we use 2-space indentation, always leaving the "#"
5465 in the first column.
5467 #ifndef PNG_NO_FEATURE
5468 # ifndef PNG_FEATURE_SUPPORTED
5469 # define PNG_FEATURE_SUPPORTED
5473 Comments appear with the leading "/*" at the same indentation as
5474 the statement that follows the comment:
5476 /* Single-line comment */
5479 /* This is a multiple-line
5484 Very short comments can be placed after the end of the statement
5485 to which they pertain:
5487 statement; /* comment */
5489 We don't use C++ style ("//") comments. We have, however,
5490 used them in the past in some now-abandoned MMX assembler
5493 Functions and their curly braces are not indented, and
5494 exported functions are marked with PNGAPI:
5496 /* This is a public function that is visible to
5497 * application programmers. It does thus-and-so.
5500 png_exported_function(png_ptr, png_info, foo)
5505 The prototypes for all exported functions appear in png.h,
5506 above the comment that says
5508 /* Maintainer: Put new public prototypes here ... */
5510 We mark all non-exported functions with "/* PRIVATE */"":
5513 png_non_exported_function(png_ptr, png_info, foo)
5518 The prototypes for non-exported functions (except for those in
5521 above the comment that says
5523 /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */
5525 To avoid polluting the global namespace, the names of all exported
5526 functions and variables begin with "png_", and all publicly visible C
5527 preprocessor macros begin with "PNG_". We request that applications that
5528 use libpng *not* begin any of their own symbols with either of these strings.
5530 We put a space after each comma and after each semicolon
5531 in "for" statements, and we put spaces before and after each
5532 C binary operator and after "for" or "while", and before
5533 "?". We don't put a space between a typecast and the expression
5534 being cast, nor do we put one between a function name and the
5535 left parenthesis that follows it:
5537 for (i = 2; i > 0; --i)
5538 y[i] = a(x) + (int)b;
5540 We prefer #ifdef and #ifndef to #if defined() and if !defined()
5541 when there is only one macro being tested.
5543 We prefer to express integers that are used as bit masks in hex format,
5544 with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100).
5546 We do not use the TAB character for indentation in the C sources.
5548 Lines do not exceed 80 characters.
5550 Other rules can be inferred by inspecting the libpng source.
5552 .SH XIV. Y2K Compliance in libpng
5556 Since the PNG Development group is an ad-hoc body, we can't make
5557 an official declaration.
5559 This is your unofficial assurance that libpng from version 0.71 and
5560 upward through 1.5.7 are Y2K compliant. It is my belief that earlier
5561 versions were also Y2K compliant.
5563 Libpng only has three year fields. One is a 2-byte unsigned integer that
5564 will hold years up to 65535. The other two hold the date in text
5565 format, and will hold years up to 9999.
5568 "png_uint_16 year" in png_time_struct.
5571 "png_charp time_buffer" in png_struct and
5572 "near_time_buffer", which is a local character string in png.c.
5574 There are seven time-related functions:
5576 png_convert_to_rfc_1123() in png.c
5577 (formerly png_convert_to_rfc_1152() in error)
5578 png_convert_from_struct_tm() in pngwrite.c, called
5580 png_convert_from_time_t() in pngwrite.c
5581 png_get_tIME() in pngget.c
5582 png_handle_tIME() in pngrutil.c, called in pngread.c
5583 png_set_tIME() in pngset.c
5584 png_write_tIME() in pngwutil.c, called in pngwrite.c
5586 All appear to handle dates properly in a Y2K environment. The
5587 png_convert_from_time_t() function calls gmtime() to convert from system
5588 clock time, which returns (year - 1900), which we properly convert to
5589 the full 4-digit year. There is a possibility that applications using
5590 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
5591 function, or that they are incorrectly passing only a 2-digit year
5592 instead of "year - 1900" into the png_convert_from_struct_tm() function,
5593 but this is not under our control. The libpng documentation has always
5594 stated that it works with 4-digit years, and the APIs have been
5597 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
5598 integer to hold the year, and can hold years as large as 65535.
5600 zlib, upon which libpng depends, is also Y2K compliant. It contains
5601 no date-related code.
5604 Glenn Randers-Pehrson
5606 PNG Development Group
5610 Note about libpng version numbers:
5612 Due to various miscommunications, unforeseen code incompatibilities
5613 and occasional factors outside the authors' control, version numbering
5614 on the library has not always been consistent and straightforward.
5615 The following table summarizes matters since version 0.89c, which was
5616 the first widely used release:
5618 source png.h png.h shared-lib
5619 version string int version
5620 ------- ------ ----- ----------
5621 0.89c ("beta 3") 0.89 89 1.0.89
5622 0.90 ("beta 4") 0.90 90 0.90
5623 0.95 ("beta 5") 0.95 95 0.95
5624 0.96 ("beta 6") 0.96 96 0.96
5625 0.97b ("beta 7") 1.00.97 97 1.0.1
5626 0.97c 0.97 97 2.0.97
5629 0.99a-m 0.99 99 2.0.99
5631 1.0.0 1.0.0 100 2.1.0
5632 1.0.0 (from here on, the 100 2.1.0
5633 1.0.1 png.h string is 10001 2.1.0
5634 1.0.1a-e identical to the 10002 from here on, the
5635 1.0.2 source version) 10002 shared library is 2.V
5636 1.0.2a-b 10003 where V is the source
5637 1.0.1 10001 code version except as
5638 1.0.1a-e 10002 2.1.0.1a-e noted.
5640 1.0.2a-b 10003 2.1.0.2a-b
5642 1.0.3a-d 10004 2.1.0.3a-d
5644 1.0.4a-f 10005 2.1.0.4a-f
5645 1.0.5 (+ 2 patches) 10005 2.1.0.5
5646 1.0.5a-d 10006 2.1.0.5a-d
5647 1.0.5e-r 10100 2.1.0.5e-r
5648 1.0.5s-v 10006 2.1.0.5s-v
5649 1.0.6 (+ 3 patches) 10006 2.1.0.6
5650 1.0.6d-g 10007 2.1.0.6d-g
5653 1.0.6j 10007 2.1.0.6j
5654 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
5655 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
5656 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
5657 1.0.7 1 10007 2.1.0.7
5658 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
5659 1.0.8rc1 1 10008 2.1.0.8rc1
5660 1.0.8 1 10008 2.1.0.8
5661 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
5662 1.0.9rc1 1 10009 2.1.0.9rc1
5663 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
5664 1.0.9rc2 1 10009 2.1.0.9rc2
5665 1.0.9 1 10009 2.1.0.9
5666 1.0.10beta1 1 10010 2.1.0.10beta1
5667 1.0.10rc1 1 10010 2.1.0.10rc1
5668 1.0.10 1 10010 2.1.0.10
5669 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
5670 1.0.11rc1 1 10011 2.1.0.11rc1
5671 1.0.11 1 10011 2.1.0.11
5672 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
5673 1.0.12rc1 2 10012 2.1.0.12rc1
5674 1.0.12 2 10012 2.1.0.12
5675 1.1.0a-f - 10100 2.1.1.0a-f abandoned
5676 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
5677 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
5678 1.2.0rc1 3 10200 3.1.2.0rc1
5679 1.2.0 3 10200 3.1.2.0
5680 1.2.1beta-4 3 10201 3.1.2.1beta1-4
5681 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
5682 1.2.1 3 10201 3.1.2.1
5683 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
5684 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
5685 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
5686 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
5687 1.0.13 10 10013 10.so.0.1.0.13
5688 1.2.2 12 10202 12.so.0.1.2.2
5689 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
5690 1.2.3 12 10203 12.so.0.1.2.3
5691 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
5692 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
5693 1.0.14 10 10014 10.so.0.1.0.14
5694 1.2.4 13 10204 12.so.0.1.2.4
5695 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
5696 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
5697 1.0.15 10 10015 10.so.0.1.0.15
5698 1.2.5 13 10205 12.so.0.1.2.5
5699 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
5700 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
5701 1.0.16 10 10016 10.so.0.1.0.16
5702 1.2.6 13 10206 12.so.0.1.2.6
5703 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
5704 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
5705 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
5706 1.0.17 10 10017 12.so.0.1.0.17
5707 1.2.7 13 10207 12.so.0.1.2.7
5708 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
5709 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
5710 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
5711 1.0.18 10 10018 12.so.0.1.0.18
5712 1.2.8 13 10208 12.so.0.1.2.8
5713 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
5714 1.2.9beta4-11 13 10209 12.so.0.9[.0]
5715 1.2.9rc1 13 10209 12.so.0.9[.0]
5716 1.2.9 13 10209 12.so.0.9[.0]
5717 1.2.10beta1-7 13 10210 12.so.0.10[.0]
5718 1.2.10rc1-2 13 10210 12.so.0.10[.0]
5719 1.2.10 13 10210 12.so.0.10[.0]
5720 1.4.0beta1-6 14 10400 14.so.0.0[.0]
5721 1.2.11beta1-4 13 10210 12.so.0.11[.0]
5722 1.4.0beta7-8 14 10400 14.so.0.0[.0]
5723 1.2.11 13 10211 12.so.0.11[.0]
5724 1.2.12 13 10212 12.so.0.12[.0]
5725 1.4.0beta9-14 14 10400 14.so.0.0[.0]
5726 1.2.13 13 10213 12.so.0.13[.0]
5727 1.4.0beta15-36 14 10400 14.so.0.0[.0]
5728 1.4.0beta37-87 14 10400 14.so.14.0[.0]
5729 1.4.0rc01 14 10400 14.so.14.0[.0]
5730 1.4.0beta88-109 14 10400 14.so.14.0[.0]
5731 1.4.0rc02-08 14 10400 14.so.14.0[.0]
5732 1.4.0 14 10400 14.so.14.0[.0]
5733 1.4.1beta01-03 14 10401 14.so.14.1[.0]
5734 1.4.1rc01 14 10401 14.so.14.1[.0]
5735 1.4.1beta04-12 14 10401 14.so.14.1[.0]
5736 1.4.1 14 10401 14.so.14.1[.0]
5737 1.4.2 14 10402 14.so.14.2[.0]
5738 1.4.3 14 10403 14.so.14.3[.0]
5739 1.4.4 14 10404 14.so.14.4[.0]
5740 1.5.0beta01-58 15 10500 15.so.15.0[.0]
5741 1.5.0rc01-07 15 10500 15.so.15.0[.0]
5742 1.5.0 15 10500 15.so.15.0[.0]
5743 1.5.1beta01-11 15 10501 15.so.15.1[.0]
5744 1.5.1rc01-02 15 10501 15.so.15.1[.0]
5745 1.5.1 15 10501 15.so.15.1[.0]
5746 1.5.2beta01-03 15 10502 15.so.15.2[.0]
5747 1.5.2rc01-03 15 10502 15.so.15.2[.0]
5748 1.5.2 15 10502 15.so.15.2[.0]
5749 1.5.3beta01-10 15 10503 15.so.15.3[.0]
5750 1.5.3rc01-02 15 10503 15.so.15.3[.0]
5751 1.5.3beta11 15 10503 15.so.15.3[.0]
5753 1.5.4beta01-08 15 10504 15.so.15.4[.0]
5754 1.5.4rc01 15 10504 15.so.15.4[.0]
5755 1.5.4 15 10504 15.so.15.4[.0]
5756 1.5.5beta01-08 15 10505 15.so.15.5[.0]
5757 1.5.5rc01 15 10505 15.so.15.5[.0]
5758 1.5.5 15 10505 15.so.15.5[.0]
5759 1.5.6beta01-07 15 10506 15.so.15.6[.0]
5760 1.5.6rc01-03 15 10506 15.so.15.6[.0]
5761 1.5.6 15 10506 15.so.15.6[.0]
5762 1.5.7beta01-05 15 10507 15.so.15.7[.0]
5763 1.5.7rc01-03 15 10507 15.so.15.7[.0]
5764 1.5.7 15 10507 15.so.15.7[.0]
5766 Henceforth the source version will match the shared-library minor
5767 and patch numbers; the shared-library major version number will be
5768 used for changes in backward compatibility, as it is intended. The
5769 PNG_PNGLIB_VER macro, which is not used within libpng but is available
5770 for applications, is an unsigned integer of the form xyyzz corresponding
5771 to the source version x.y.z (leading zeros in y and z). Beta versions
5772 were given the previous public release number plus a letter, until
5773 version 1.0.6j; from then on they were given the upcoming public
5774 release number plus "betaNN" or "rcN".
5777 .BR "png"(5), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
5782 http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
5783 http://www.libpng.org/pub/png
5788 (generally) at the same location as
5792 ftp://ftp.info-zip.org/pub/infozip/zlib
5795 .IR PNG specification: RFC 2083
5797 (generally) at the same location as
5801 ftp://ds.internic.net/rfc/rfc2083.txt
5803 or (as a W3C Recommendation) at
5805 http://www.w3.org/TR/REC-png.html
5808 In the case of any inconsistency between the PNG specification
5809 and this library, the specification takes precedence.
5812 This man page: Glenn Randers-Pehrson
5813 <glennrp at users.sourceforge.net>
5815 The contributing authors would like to thank all those who helped
5816 with testing, bug fixes, and patience. This wouldn't have been
5817 possible without all of you.
5819 Thanks to Frank J. T. Wojcik for helping with the documentation.
5821 Libpng version 1.5.7 - December 15, 2011:
5822 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
5823 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
5825 Supported by the PNG development group
5827 png-mng-implement at lists.sf.net
5828 (subscription required; visit
5829 png-mng-implement at lists.sourceforge.net (subscription required; visit
5830 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
5833 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
5835 (This copy of the libpng notices is provided for your convenience. In case of
5836 any discrepancy between this copy and the notices in the file png.h that is
5837 included in the libpng distribution, the latter shall prevail.)
5839 If you modify libpng you may insert additional notices immediately following
5842 This code is released under the libpng license.
5844 libpng versions 1.2.6, August 15, 2004, through 1.5.7, December 15, 2011, are
5845 Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
5846 distributed according to the same disclaimer and license as libpng-1.2.5
5847 with the following individual added to the list of Contributing Authors
5851 libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
5852 Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
5853 distributed according to the same disclaimer and license as libpng-1.0.6
5854 with the following individuals added to the list of Contributing Authors
5856 Simon-Pierre Cadieux
5860 and with the following additions to the disclaimer:
5862 There is no warranty against interference with your
5863 enjoyment of the library or against infringement.
5864 There is no warranty that our efforts or the library
5865 will fulfill any of your particular purposes or needs.
5866 This library is provided with all faults, and the entire
5867 risk of satisfactory quality, performance, accuracy, and
5868 effort is with the user.
5870 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
5871 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
5872 Distributed according to the same disclaimer and license as libpng-0.96,
5873 with the following individuals added to the list of Contributing Authors:
5876 Glenn Randers-Pehrson
5879 libpng versions 0.89, June 1996, through 0.96, May 1997, are
5880 Copyright (c) 1996, 1997 Andreas Dilger
5881 Distributed according to the same disclaimer and license as libpng-0.88,
5882 with the following individuals added to the list of Contributing Authors:
5891 libpng versions 0.5, May 1995, through 0.88, January 1996, are
5892 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
5894 For the purposes of this copyright and license, "Contributing Authors"
5895 is defined as the following set of individuals:
5903 The PNG Reference Library is supplied "AS IS". The Contributing Authors
5904 and Group 42, Inc. disclaim all warranties, expressed or implied,
5905 including, without limitation, the warranties of merchantability and of
5906 fitness for any purpose. The Contributing Authors and Group 42, Inc.
5907 assume no liability for direct, indirect, incidental, special, exemplary,
5908 or consequential damages, which may result from the use of the PNG
5909 Reference Library, even if advised of the possibility of such damage.
5911 Permission is hereby granted to use, copy, modify, and distribute this
5912 source code, or portions hereof, for any purpose, without fee, subject
5913 to the following restrictions:
5915 1. The origin of this source code must not be misrepresented.
5917 2. Altered versions must be plainly marked as such and
5918 must not be misrepresented as being the original source.
5920 3. This Copyright notice may not be removed or altered from
5921 any source or altered source distribution.
5923 The Contributing Authors and Group 42, Inc. specifically permit, without
5924 fee, and encourage the use of this source code as a component to
5925 supporting the PNG file format in commercial products. If you use this
5926 source code in a product, acknowledgment is not required but would be
5930 A "png_get_copyright" function is available, for convenient use in "about"
5933 printf("%s",png_get_copyright(NULL));
5935 Also, the PNG logo (in PNG format, of course) is supplied in the
5936 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
5938 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
5939 certification mark of the Open Source Initiative.
5941 Glenn Randers-Pehrson
5942 glennrp at users.sourceforge.net
projects / wxWidgets.git / blob