1 .TH LIBPNG 3 "December 18, 2008"
3 libpng \- Portable Network Graphics (PNG) Reference Library 1.2.34
11 \fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
15 \fBint png_check_sig (png_bytep \fP\fIsig\fP\fB, int \fInum\fP\fB);\fP
19 \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
23 \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
27 \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
31 \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
35 \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
39 \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
43 \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
47 \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
51 \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
55 \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
59 \fBint png_debug(int \fP\fIlevel\fP\fB, png_const_charp \fImessage\fP\fB);\fP
63 \fBint png_debug1(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fIp1\fP\fB);\fP
67 \fBint png_debug2(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fP\fIp1\fP\fB, \fIp2\fP\fB);\fP
71 \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
75 \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
79 \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
83 \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
87 \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
91 \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
95 \fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
99 \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
103 \fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
107 \fBpng_uint_32 png_get_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
111 \fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
115 \fBpng_uint_32 png_get_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_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
119 \fBpng_uint_32 png_get_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_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
123 \fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
127 \fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
131 \fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
135 \fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
139 \fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
143 \fBpng_uint_32 png_get_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
147 \fBpng_uint_32 png_get_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
151 \fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
155 \fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
159 \fBpng_uint_32 png_get_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
163 \fBpng_uint_32 png_get_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_charpp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
167 \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
171 \fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
175 \fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
179 \fB#if \fI!defined(PNG_1_0_X)
181 \fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
187 \fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
191 \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
195 \fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
199 \fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
203 \fBpng_uint_32 png_get_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_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
207 \fBpng_uint_32 png_get_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_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
211 \fBpng_uint_32 png_get_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_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
215 \fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
219 \fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
223 \fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
227 \fBpng_uint_32 png_get_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
231 \fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
233 \fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
237 \fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
241 \fBpng_uint_32 png_get_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
245 \fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
249 \fBpng_uint_32 png_get_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
253 \fBpng_uint_32 png_get_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fI*intent\fP\fB);\fP
257 \fBpng_uint_32 png_get_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
261 \fBpng_uint_32 png_get_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
265 \fBpng_uint_32 png_get_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_values\fP\fB);\fP
269 \fB#if \fI!defined(PNG_1_0_X)
271 \fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
275 \fBpng_uint_32 png_get_uint_31 (png_bytep \fIbuf\fP\fB);\fP
279 \fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
285 \fBpng_uint_32 png_get_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
289 \fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
293 \fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
297 \fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
301 \fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
305 \fBpng_uint_32 png_get_valid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
309 \fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
313 \fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
317 \fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
321 \fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
325 \fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
329 \fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
333 \fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
337 \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
341 \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
345 \fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
349 \fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
353 \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
357 \fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
361 \fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
365 \fBpng_voidp png_memcpy_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
369 \fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
373 \fBpng_voidp png_memset_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
377 \fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
381 \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
385 \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
389 \fBvoid png_read_destroy (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_infop \fIend_info_ptr\fP\fB);\fP
393 \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
397 \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
401 \fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
405 \fBDEPRECATED: void png_read_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
409 \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
413 \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
417 \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
421 \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
425 \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
429 \fB#if \fI!defined(PNG_1_0_X)
431 \fBpng_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
435 \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
439 \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
443 \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
449 \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
453 \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
457 \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
461 \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
465 \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
469 \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
473 \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
477 \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
481 \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
485 \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
489 \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
493 \fBvoid png_set_dither (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_dither\fP\fB);\fP
497 \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
501 \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
505 \fBvoid png_set_expand_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
509 \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
513 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
517 \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
521 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
525 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
529 \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
533 \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
537 \fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
541 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
545 \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
549 \fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_charp \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
553 \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
557 \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
561 \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
565 \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
569 \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
573 \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
577 \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
581 \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
585 \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
589 \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
593 \fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
597 \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
601 \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
605 \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
609 \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
613 \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
617 \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
621 \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
625 \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
629 \fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_fixed_point \fP\fIred\fP\fB, png_fixed_point \fIgreen\fP\fB);\fP
633 \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
637 \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
641 \fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
645 \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
649 \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
653 \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
657 \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
661 \fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
665 \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
669 \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
673 \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
677 \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
681 \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
685 \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
689 \fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_values\fP\fB);\fP
693 \fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
697 \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
701 \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
705 \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
709 \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
713 \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
717 \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
721 \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
725 \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
729 \fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
733 \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
737 \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
741 \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
745 \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
749 \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
753 \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
757 \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
761 \fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
765 \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
769 \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
773 \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
777 \fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
781 \fBDEPRECATED: void png_write_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
785 \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
789 \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
793 \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
797 \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
801 \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
805 \fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
809 \fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
816 library supports encoding, decoding, and various manipulations of
817 the Portable Network Graphics (PNG) format image files. It uses the
820 Following is a copy of the libpng.txt file that accompanies libpng.
822 libpng.txt - A description on how to use and modify libpng
824 libpng version 1.2.34 - December 18, 2008
825 Updated and distributed by Glenn Randers-Pehrson
826 <glennrp at users.sourceforge.net>
827 Copyright (c) 1998-2008 Glenn Randers-Pehrson
828 For conditions of distribution and use, see copyright
833 libpng versions 0.97, January 1998, through 1.2.34 - December 18, 2008
834 Updated and distributed by Glenn Randers-Pehrson
835 Copyright (c) 1998-2008 Glenn Randers-Pehrson
837 libpng 1.0 beta 6 version 0.96 May 28, 1997
838 Updated and distributed by Andreas Dilger
839 Copyright (c) 1996, 1997 Andreas Dilger
841 libpng 1.0 beta 2 - version 0.88 January 26, 1996
842 For conditions of distribution and use, see copyright
843 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
844 Schalnat, Group 42, Inc.
846 Updated/rewritten per request in the libpng FAQ
847 Copyright (c) 1995, 1996 Frank J. T. Wojcik
848 December 18, 1995 & January 20, 1996
852 This file describes how to use and modify the PNG reference library
853 (known as libpng) for your own use. There are five sections to this
854 file: introduction, structures, reading, writing, and modification and
855 configuration notes for various special platforms. In addition to this
856 file, example.c is a good starting point for using the library, as
857 it is heavily commented and should include everything most people
858 will need. We assume that libpng is already installed; see the
859 INSTALL file for instructions on how to install libpng.
861 For examples of libpng usage, see the files "example.c", "pngtest.c",
862 and the files in the "contrib" directory, all of which are included in the
865 Libpng was written as a companion to the PNG specification, as a way
866 of reducing the amount of time and effort it takes to support the PNG
867 file format in application programs.
869 The PNG specification (second edition), November 2003, is available as
870 a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
871 <http://www.w3.org/TR/2003/REC-PNG-20031110/
872 The W3C and ISO documents have identical technical content.
874 The PNG-1.2 specification is available at
875 <http://www.libpng.org/pub/png/documents/>. It is technically equivalent
876 to the PNG specification (second edition) but has some additional material.
878 The PNG-1.0 specification is available
879 as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
880 W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
882 Some additional chunks are described in the special-purpose public chunks
883 documents at <http://www.libpng.org/pub/png/documents/>.
886 about PNG, and the latest version of libpng, can be found at the PNG home
887 page, <http://www.libpng.org/pub/png/>.
889 Most users will not have to modify the library significantly; advanced
890 users may want to modify it more. All attempts were made to make it as
891 complete as possible, while keeping the code easy to understand.
892 Currently, this library only supports C. Support for other languages
895 Libpng has been designed to handle multiple sessions at one time,
896 to be easily modifiable, to be portable to the vast majority of
897 machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
898 to use. The ultimate goal of libpng is to promote the acceptance of
899 the PNG file format in whatever way possible. While there is still
900 work to be done (see the TODO file), libpng should cover the
901 majority of the needs of its users.
903 Libpng uses zlib for its compression and decompression of PNG files.
904 Further information about zlib, and the latest version of zlib, can
905 be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
906 The zlib compression utility is a general purpose utility that is
907 useful for more than PNG files, and can be used without libpng.
908 See the documentation delivered with zlib for more details.
909 You can usually find the source files for the zlib utility wherever you
910 find the libpng source files.
912 Libpng is thread safe, provided the threads are using different
913 instances of the structures. Each thread should have its own
914 png_struct and png_info instances, and thus its own image.
915 Libpng does not protect itself against two threads using the
916 same instance of a structure.
920 There are two main structures that are important to libpng, png_struct
921 and png_info. The first, png_struct, is an internal structure that
922 will not, for the most part, be used by a user except as the first
923 variable passed to every libpng function call.
925 The png_info structure is designed to provide information about the
926 PNG file. At one time, the fields of png_info were intended to be
927 directly accessible to the user. However, this tended to cause problems
928 with applications using dynamically loaded libraries, and as a result
929 a set of interface functions for png_info (the png_get_*() and png_set_*()
930 functions) was developed. The fields of png_info are still available for
931 older applications, but it is suggested that applications use the new
932 interfaces if at all possible.
934 Applications that do make direct access to the members of png_struct (except
935 for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
936 and applications that make direct access to the members of png_info must
937 be recompiled if they were compiled or loaded with libpng version 1.0.6,
938 in which the members were in a different order. In version 1.0.7, the
939 members of the png_info structure reverted to the old order, as they were
940 in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
941 structures are going to be hidden, and the contents of the structures will
942 only be accessible through the png_get/png_set functions.
944 The png.h header file is an invaluable reference for programming with libpng.
945 And while I'm on the topic, make sure you include the libpng header file:
951 We'll now walk you through the possible functions to call when reading
952 in a PNG file sequentially, briefly explaining the syntax and purpose
953 of each one. See example.c and png.h for more detail. While
954 progressive reading is covered in the next section, you will still
955 need some of the functions discussed in this section to read a PNG
960 You will want to do the I/O initialization(*) before you get into libpng,
961 so if it doesn't work, you don't have much to undo. Of course, you
962 will also want to insure that you are, in fact, dealing with a PNG
963 file. Libpng provides a simple check to see if a file is a PNG file.
964 To use it, pass in the first 1 to 8 bytes of the file to the function
965 png_sig_cmp(), and it will return 0 if the bytes match the corresponding
966 bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
967 you pass in, the greater the accuracy of the prediction.
969 If you are intending to keep the file pointer open for use in libpng,
970 you must ensure you don't read more than 8 bytes from the beginning
971 of the file, and you also have to make a call to png_set_sig_bytes_read()
972 with the number of bytes you read from the beginning. Libpng will
973 then only check the bytes (if any) that your program didn't read.
975 (*): If you are not using the standard I/O functions, you will need
976 to replace them with custom functions. See the discussion under
980 FILE *fp = fopen(file_name, "rb");
985 fread(header, 1, number, fp);
986 is_png = !png_sig_cmp(header, 0, number);
993 Next, png_struct and png_info need to be allocated and initialized. In
994 order to ensure that the size of these structures is correct even with a
995 dynamically linked libpng, there are functions to initialize and
996 allocate the structures. We also pass the library version, optional
997 pointers to error handling functions, and a pointer to a data struct for
998 use by the error functions, if necessary (the pointer and functions can
999 be NULL if the default error handlers are to be used). See the section
1000 on Changes to Libpng below regarding the old initialization functions.
1001 The structure allocation functions quietly return NULL if they fail to
1002 create the structure, so your application should check for that.
1004 png_structp png_ptr = png_create_read_struct
1005 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1006 user_error_fn, user_warning_fn);
1010 png_infop info_ptr = png_create_info_struct(png_ptr);
1013 png_destroy_read_struct(&png_ptr,
1014 (png_infopp)NULL, (png_infopp)NULL);
1018 png_infop end_info = png_create_info_struct(png_ptr);
1021 png_destroy_read_struct(&png_ptr, &info_ptr,
1026 If you want to use your own memory allocation routines,
1027 define PNG_USER_MEM_SUPPORTED and use
1028 png_create_read_struct_2() instead of png_create_read_struct():
1030 png_structp png_ptr = png_create_read_struct_2
1031 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
1032 user_error_fn, user_warning_fn, (png_voidp)
1033 user_mem_ptr, user_malloc_fn, user_free_fn);
1035 The error handling routines passed to png_create_read_struct()
1036 and the memory alloc/free routines passed to png_create_struct_2()
1037 are only necessary if you are not using the libpng supplied error
1038 handling and memory alloc/free functions.
1040 When libpng encounters an error, it expects to longjmp back
1041 to your routine. Therefore, you will need to call setjmp and pass
1042 your png_jmpbuf(png_ptr). If you read the file from different
1043 routines, you will need to update the jmpbuf field every time you enter
1044 a new routine that will call a png_*() function.
1046 See your documentation of setjmp/longjmp for your compiler for more
1047 information on setjmp/longjmp. See the discussion on libpng error
1048 handling in the Customizing Libpng section below for more information
1049 on the libpng error handling. If an error occurs, and libpng longjmp's
1050 back to your setjmp, you will want to call png_destroy_read_struct() to
1053 if (setjmp(png_jmpbuf(png_ptr)))
1055 png_destroy_read_struct(&png_ptr, &info_ptr,
1061 If you would rather avoid the complexity of setjmp/longjmp issues,
1062 you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
1063 errors will result in a call to PNG_ABORT() which defaults to abort().
1065 Now you need to set up the input code. The default for libpng is to
1066 use the C function fread(). If you use this, you will need to pass a
1067 valid FILE * in the function png_init_io(). Be sure that the file is
1068 opened in binary mode. If you wish to handle reading data in another
1069 way, you need not call the png_init_io() function, but you must then
1070 implement the libpng I/O methods discussed in the Customizing Libpng
1073 png_init_io(png_ptr, fp);
1075 If you had previously opened the file and read any of the signature from
1076 the beginning in order to see if this was a PNG file, you need to let
1077 libpng know that there are some bytes missing from the start of the file.
1079 png_set_sig_bytes(png_ptr, number);
1081 .SS Setting up callback code
1083 You can set up a callback function to handle any unknown chunks in the
1084 input stream. You must supply the function
1086 read_chunk_callback(png_ptr ptr,
1087 png_unknown_chunkp chunk);
1089 /* The unknown chunk structure contains your
1090 chunk data, along with similar data for any other
1097 /* Note that libpng has already taken care of
1100 /* put your code here. Search for your chunk in the
1101 unknown chunk structure, process it, and return one
1102 of the following: */
1104 return (-n); /* chunk had an error */
1105 return (0); /* did not recognize */
1106 return (n); /* success */
1109 (You can give your function another name that you like instead of
1110 "read_chunk_callback")
1112 To inform libpng about your function, use
1114 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1115 read_chunk_callback);
1117 This names not only the callback function, but also a user pointer that
1118 you can retrieve with
1120 png_get_user_chunk_ptr(png_ptr);
1122 If you call the png_set_read_user_chunk_fn() function, then all unknown
1123 chunks will be saved when read, in case your callback function will need
1124 one or more of them. This behavior can be changed with the
1125 png_set_keep_unknown_chunks() function, described below.
1127 At this point, you can set up a callback function that will be
1128 called after each row has been read, which you can use to control
1129 a progress meter or the like. It's demonstrated in pngtest.c.
1130 You must supply a function
1132 void read_row_callback(png_ptr ptr, png_uint_32 row,
1135 /* put your code here */
1138 (You can give it another name that you like instead of "read_row_callback")
1140 To inform libpng about your function, use
1142 png_set_read_status_fn(png_ptr, read_row_callback);
1144 .SS Width and height limits
1146 The PNG specification allows the width and height of an image to be as
1147 large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
1148 Since very few applications really need to process such large images,
1149 we have imposed an arbitrary 1-million limit on rows and columns.
1150 Larger images will be rejected immediately with a png_error() call. If
1151 you wish to override this limit, you can use
1153 png_set_user_limits(png_ptr, width_max, height_max);
1155 to set your own limits, or use width_max = height_max = 0x7fffffffL
1156 to allow all valid dimensions (libpng may reject some very large images
1157 anyway because of potential buffer overflow conditions).
1159 You should put this statement after you create the PNG structure and
1160 before calling png_read_info(), png_read_png(), or png_process_data().
1161 If you need to retrieve the limits that are being applied, use
1163 width_max = png_get_user_width_max(png_ptr);
1164 height_max = png_get_user_height_max(png_ptr);
1166 .SS Unknown-chunk handling
1168 Now you get to set the way the library processes unknown chunks in the
1169 input PNG stream. Both known and unknown chunks will be read. Normal
1170 behavior is that known chunks will be parsed into information in
1171 various info_ptr members while unknown chunks will be discarded. This
1172 behavior can be wasteful if your application will never use some known
1173 chunk types. To change this, you can call:
1175 png_set_keep_unknown_chunks(png_ptr, keep,
1176 chunk_list, num_chunks);
1177 keep - 0: default unknown chunk handling
1178 1: ignore; do not keep
1179 2: keep only if safe-to-copy
1180 3: keep even if unsafe-to-copy
1181 You can use these definitions:
1182 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1183 PNG_HANDLE_CHUNK_NEVER 1
1184 PNG_HANDLE_CHUNK_IF_SAFE 2
1185 PNG_HANDLE_CHUNK_ALWAYS 3
1186 chunk_list - list of chunks affected (a byte string,
1187 five bytes per chunk, NULL or '\0' if
1189 num_chunks - number of chunks affected; if 0, all
1190 unknown chunks are affected. If nonzero,
1191 only the chunks in the list are affected
1193 Unknown chunks declared in this way will be saved as raw data onto a
1194 list of png_unknown_chunk structures. If a chunk that is normally
1195 known to libpng is named in the list, it will be handled as unknown,
1196 according to the "keep" directive. If a chunk is named in successive
1197 instances of png_set_keep_unknown_chunks(), the final instance will
1198 take precedence. The IHDR and IEND chunks should not be named in
1199 chunk_list; if they are, libpng will process them normally anyway.
1201 Here is an example of the usage of png_set_keep_unknown_chunks(),
1202 where the private "vpAg" chunk will later be processed by a user chunk
1205 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1207 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1208 png_byte unused_chunks[]=
1210 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1211 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1212 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1213 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1214 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1215 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1221 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1222 /* ignore all unknown chunks: */
1223 png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
1224 /* except for vpAg: */
1225 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
1226 /* also ignore unused known chunks: */
1227 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
1228 (int)sizeof(unused_chunks)/5);
1232 .SS The high-level read interface
1234 At this point there are two ways to proceed; through the high-level
1235 read interface, or through a sequence of low-level read operations.
1236 You can use the high-level interface if (a) you are willing to read
1237 the entire image into memory, and (b) the input transformations
1238 you want to do are limited to the following set:
1240 PNG_TRANSFORM_IDENTITY No transformation
1241 PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
1243 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1244 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1246 PNG_TRANSFORM_PACKSWAP Change order of packed
1248 PNG_TRANSFORM_EXPAND Perform set_expand()
1249 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1250 PNG_TRANSFORM_SHIFT Normalize pixels to the
1252 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1254 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1256 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1258 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
1260 (This excludes setting a background color, doing gamma transformation,
1261 dithering, and setting filler.) If this is the case, simply do this:
1263 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1265 where png_transforms is an integer containing the bitwise OR of
1266 some set of transformation flags. This call is equivalent to png_read_info(),
1267 followed the set of transformations indicated by the transform mask,
1268 then png_read_image(), and finally png_read_end().
1270 (The final parameter of this call is not yet used. Someday it might point
1271 to transformation parameters required by some future input transform.)
1273 You must use png_transforms and not call any png_set_transform() functions
1274 when you use png_read_png().
1276 After you have called png_read_png(), you can retrieve the image data
1279 row_pointers = png_get_rows(png_ptr, info_ptr);
1281 where row_pointers is an array of pointers to the pixel data for each row:
1283 png_bytep row_pointers[height];
1285 If you know your image size and pixel size ahead of time, you can allocate
1286 row_pointers prior to calling png_read_png() with
1288 if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
1290 "Image is too tall to process in memory");
1291 if (width > PNG_UINT_32_MAX/pixel_size)
1293 "Image is too wide to process in memory");
1294 row_pointers = png_malloc(png_ptr,
1295 height*png_sizeof(png_bytep));
1296 for (int i=0; i<height, i++)
1297 row_pointers[i]=png_malloc(png_ptr,
1299 png_set_rows(png_ptr, info_ptr, &row_pointers);
1301 Alternatively you could allocate your image in one big block and define
1302 row_pointers[i] to point into the proper places in your block.
1304 If you use png_set_rows(), the application is responsible for freeing
1305 row_pointers (and row_pointers[i], if they were separately allocated).
1307 If you don't allocate row_pointers ahead of time, png_read_png() will
1308 do it, and it'll be free'ed when you call png_destroy_*().
1310 .SS The low-level read interface
1312 If you are going the low-level route, you are now ready to read all
1313 the file information up to the actual image data. You do this with a
1314 call to png_read_info().
1316 png_read_info(png_ptr, info_ptr);
1318 This will process all chunks up to but not including the image data.
1320 .SS Querying the info structure
1322 Functions are used to get the information from the info_ptr once it
1323 has been read. Note that these fields may not be completely filled
1324 in until png_read_end() has read the chunk data following the image.
1326 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1327 &bit_depth, &color_type, &interlace_type,
1328 &compression_type, &filter_method);
1330 width - holds the width of the image
1331 in pixels (up to 2^31).
1332 height - holds the height of the image
1333 in pixels (up to 2^31).
1334 bit_depth - holds the bit depth of one of the
1335 image channels. (valid values are
1336 1, 2, 4, 8, 16 and depend also on
1337 the color_type. See also
1338 significant bits (sBIT) below).
1339 color_type - describes which color/alpha channels
1342 (bit depths 1, 2, 4, 8, 16)
1343 PNG_COLOR_TYPE_GRAY_ALPHA
1345 PNG_COLOR_TYPE_PALETTE
1346 (bit depths 1, 2, 4, 8)
1349 PNG_COLOR_TYPE_RGB_ALPHA
1352 PNG_COLOR_MASK_PALETTE
1353 PNG_COLOR_MASK_COLOR
1354 PNG_COLOR_MASK_ALPHA
1356 filter_method - (must be PNG_FILTER_TYPE_BASE
1357 for PNG 1.0, and can also be
1358 PNG_INTRAPIXEL_DIFFERENCING if
1359 the PNG datastream is embedded in
1360 a MNG-1.0 datastream)
1361 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1363 interlace_type - (PNG_INTERLACE_NONE or
1364 PNG_INTERLACE_ADAM7)
1365 Any or all of interlace_type, compression_type, of
1366 filter_method can be NULL if you are
1367 not interested in their values.
1369 channels = png_get_channels(png_ptr, info_ptr);
1370 channels - number of channels of info for the
1371 color type (valid values are 1 (GRAY,
1372 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1373 4 (RGB_ALPHA or RGB + filler byte))
1374 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
1375 rowbytes - number of bytes needed to hold a row
1377 signature = png_get_signature(png_ptr, info_ptr);
1378 signature - holds the signature read from the
1379 file (if any). The data is kept in
1380 the same offset it would be if the
1381 whole signature were read (i.e. if an
1382 application had already read in 4
1383 bytes of signature before starting
1384 libpng, the remaining 4 bytes would
1385 be in signature[4] through signature[7]
1386 (see png_set_sig_bytes())).
1389 width = png_get_image_width(png_ptr,
1391 height = png_get_image_height(png_ptr,
1393 bit_depth = png_get_bit_depth(png_ptr,
1395 color_type = png_get_color_type(png_ptr,
1397 filter_method = png_get_filter_type(png_ptr,
1399 compression_type = png_get_compression_type(png_ptr,
1401 interlace_type = png_get_interlace_type(png_ptr,
1405 These are also important, but their validity depends on whether the chunk
1406 has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1407 png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1408 data has been read, or zero if it is missing. The parameters to the
1409 png_get_<chunk> are set directly if they are simple data types, or a pointer
1410 into the info_ptr is returned for any complex types.
1412 png_get_PLTE(png_ptr, info_ptr, &palette,
1414 palette - the palette for the file
1415 (array of png_color)
1416 num_palette - number of entries in the palette
1418 png_get_gAMA(png_ptr, info_ptr, &gamma);
1419 gamma - the gamma the file is written
1422 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
1423 srgb_intent - the rendering intent (PNG_INFO_sRGB)
1424 The presence of the sRGB chunk
1425 means that the pixel data is in the
1426 sRGB color space. This chunk also
1427 implies specific values of gAMA and
1430 png_get_iCCP(png_ptr, info_ptr, &name,
1431 &compression_type, &profile, &proflen);
1432 name - The profile name.
1433 compression - The compression type; always
1434 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1435 You may give NULL to this argument to
1437 profile - International Color Consortium color
1438 profile data. May contain NULs.
1439 proflen - length of profile data in bytes.
1441 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
1442 sig_bit - the number of significant bits for
1443 (PNG_INFO_sBIT) each of the gray,
1444 red, green, and blue channels,
1445 whichever are appropriate for the
1446 given color type (png_color_16)
1448 png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
1450 trans - array of transparent entries for
1451 palette (PNG_INFO_tRNS)
1452 trans_values - graylevel or color sample values of
1453 the single transparent color for
1454 non-paletted images (PNG_INFO_tRNS)
1455 num_trans - number of transparent entries
1458 png_get_hIST(png_ptr, info_ptr, &hist);
1460 hist - histogram of palette (array of
1463 png_get_tIME(png_ptr, info_ptr, &mod_time);
1464 mod_time - time image was last modified
1467 png_get_bKGD(png_ptr, info_ptr, &background);
1468 background - background color (PNG_VALID_bKGD)
1469 valid 16-bit red, green and blue
1470 values, regardless of color_type
1472 num_comments = png_get_text(png_ptr, info_ptr,
1473 &text_ptr, &num_text);
1474 num_comments - number of comments
1475 text_ptr - array of png_text holding image
1477 text_ptr[i].compression - type of compression used
1478 on "text" PNG_TEXT_COMPRESSION_NONE
1479 PNG_TEXT_COMPRESSION_zTXt
1480 PNG_ITXT_COMPRESSION_NONE
1481 PNG_ITXT_COMPRESSION_zTXt
1482 text_ptr[i].key - keyword for comment. Must contain
1484 text_ptr[i].text - text comments for current
1485 keyword. Can be empty.
1486 text_ptr[i].text_length - length of text string,
1487 after decompression, 0 for iTXt
1488 text_ptr[i].itxt_length - length of itxt string,
1489 after decompression, 0 for tEXt/zTXt
1490 text_ptr[i].lang - language of comment (empty
1491 string for unknown).
1492 text_ptr[i].lang_key - keyword in UTF-8
1493 (empty string for unknown).
1494 num_text - number of comments (same as
1495 num_comments; you can put NULL here
1496 to avoid the duplication)
1497 Note while png_set_text() will accept text, language,
1498 and translated keywords that can be NULL pointers, the
1499 structure returned by png_get_text will always contain
1500 regular zero-terminated C strings. They might be
1501 empty strings but they will never be NULL pointers.
1503 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
1505 palette_ptr - array of palette structures holding
1506 contents of one or more sPLT chunks
1508 num_spalettes - number of sPLT chunks read.
1510 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
1512 offset_x - positive offset from the left edge
1514 offset_y - positive offset from the top edge
1516 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
1518 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
1520 res_x - pixels/unit physical resolution in
1522 res_y - pixels/unit physical resolution in
1524 unit_type - PNG_RESOLUTION_UNKNOWN,
1525 PNG_RESOLUTION_METER
1527 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
1529 unit - physical scale units (an integer)
1530 width - width of a pixel in physical scale units
1531 height - height of a pixel in physical scale units
1532 (width and height are doubles)
1534 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
1536 unit - physical scale units (an integer)
1537 width - width of a pixel in physical scale units
1538 height - height of a pixel in physical scale units
1539 (width and height are strings like "2.54")
1541 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
1542 info_ptr, &unknowns)
1543 unknowns - array of png_unknown_chunk
1544 structures holding unknown chunks
1545 unknowns[i].name - name of unknown chunk
1546 unknowns[i].data - data of unknown chunk
1547 unknowns[i].size - size of unknown chunk's data
1548 unknowns[i].location - position of chunk in file
1550 The value of "i" corresponds to the order in which the
1551 chunks were read from the PNG file or inserted with the
1552 png_set_unknown_chunks() function.
1554 The data from the pHYs chunk can be retrieved in several convenient
1557 res_x = png_get_x_pixels_per_meter(png_ptr,
1559 res_y = png_get_y_pixels_per_meter(png_ptr,
1561 res_x_and_y = png_get_pixels_per_meter(png_ptr,
1563 res_x = png_get_x_pixels_per_inch(png_ptr,
1565 res_y = png_get_y_pixels_per_inch(png_ptr,
1567 res_x_and_y = png_get_pixels_per_inch(png_ptr,
1569 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
1572 (Each of these returns 0 [signifying "unknown"] if
1573 the data is not present or if res_x is 0;
1574 res_x_and_y is 0 if res_x != res_y)
1576 The data from the oFFs chunk can be retrieved in several convenient
1579 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
1580 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
1581 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
1582 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
1584 (Each of these returns 0 [signifying "unknown" if both
1585 x and y are 0] if the data is not present or if the
1586 chunk is present but the unit is the pixel)
1588 For more information, see the png_info definition in png.h and the
1589 PNG specification for chunk contents. Be careful with trusting
1590 rowbytes, as some of the transformations could increase the space
1591 needed to hold a row (expand, filler, gray_to_rgb, etc.).
1592 See png_read_update_info(), below.
1594 A quick word about text_ptr and num_text. PNG stores comments in
1595 keyword/text pairs, one pair per chunk, with no limit on the number
1596 of text chunks, and a 2^31 byte limit on their size. While there are
1597 suggested keywords, there is no requirement to restrict the use to these
1598 strings. It is strongly suggested that keywords and text be sensible
1599 to humans (that's the point), so don't use abbreviations. Non-printing
1600 symbols are not allowed. See the PNG specification for more details.
1601 There is also no requirement to have text after the keyword.
1603 Keywords should be limited to 79 Latin-1 characters without leading or
1604 trailing spaces, but non-consecutive spaces are allowed within the
1605 keyword. It is possible to have the same keyword any number of times.
1606 The text_ptr is an array of png_text structures, each holding a
1607 pointer to a language string, a pointer to a keyword and a pointer to
1608 a text string. The text string, language code, and translated
1609 keyword may be empty or NULL pointers. The keyword/text
1610 pairs are put into the array in the order that they are received.
1611 However, some or all of the text chunks may be after the image, so, to
1612 make sure you have read all the text chunks, don't mess with these
1613 until after you read the stuff after the image. This will be
1614 mentioned again below in the discussion that goes with png_read_end().
1616 .SS Input transformations
1618 After you've read the header information, you can set up the library
1619 to handle any special transformations of the image data. The various
1620 ways to transform the data will be described in the order that they
1621 should occur. This is important, as some of these change the color
1622 type and/or bit depth of the data, and some others only work on
1623 certain color types and bit depths. Even though each transformation
1624 checks to see if it has data that it can do something with, you should
1625 make sure to only enable a transformation if it will be valid for the
1626 data. For example, don't swap red and blue on grayscale data.
1628 The colors used for the background and transparency values should be
1629 supplied in the same format/depth as the current image data. They
1630 are stored in the same format/depth as the image data in a bKGD or tRNS
1631 chunk, so this is what libpng expects for this data. The colors are
1632 transformed to keep in sync with the image data when an application
1633 calls the png_read_update_info() routine (see below).
1635 Data will be decoded into the supplied row buffers packed into bytes
1636 unless the library has been told to transform it into another format.
1637 For example, 4 bit/pixel paletted or grayscale data will be returned
1638 2 pixels/byte with the leftmost pixel in the high-order bits of the
1639 byte, unless png_set_packing() is called. 8-bit RGB data will be stored
1640 in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
1641 is called to insert filler bytes, either before or after each RGB triplet.
1642 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
1643 byte of the color value first, unless png_set_strip_16() is called to
1644 transform it to regular RGB RGB triplets, or png_set_filler() or
1645 png_set_add alpha() is called to insert filler bytes, either before or
1646 after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
1648 png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
1650 The following code transforms grayscale images of less than 8 to 8 bits,
1651 changes paletted images to RGB, and adds a full alpha channel if there is
1652 transparency information in a tRNS chunk. This is most useful on
1653 grayscale images with bit depths of 2 or 4 or if there is a multiple-image
1654 viewing application that wishes to treat all images in the same way.
1656 if (color_type == PNG_COLOR_TYPE_PALETTE)
1657 png_set_palette_to_rgb(png_ptr);
1659 if (color_type == PNG_COLOR_TYPE_GRAY &&
1660 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
1662 if (png_get_valid(png_ptr, info_ptr,
1663 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
1665 These three functions are actually aliases for png_set_expand(), added
1666 in libpng version 1.0.4, with the function names expanded to improve code
1667 readability. In some future version they may actually do different
1670 As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
1671 added. It expands the sample depth without changing tRNS to alpha.
1672 At the same time, png_set_gray_1_2_4_to_8() was deprecated, and it
1673 will be removed from a future version.
1676 PNG can have files with 16 bits per channel. If you only can handle
1677 8 bits per channel, this will strip the pixels down to 8 bit.
1679 if (bit_depth == 16)
1680 png_set_strip_16(png_ptr);
1682 If, for some reason, you don't need the alpha channel on an image,
1683 and you want to remove it rather than combining it with the background
1684 (but the image author certainly had in mind that you *would* combine
1685 it with the background, so that's what you should probably do):
1687 if (color_type & PNG_COLOR_MASK_ALPHA)
1688 png_set_strip_alpha(png_ptr);
1690 In PNG files, the alpha channel in an image
1691 is the level of opacity. If you need the alpha channel in an image to
1692 be the level of transparency instead of opacity, you can invert the
1693 alpha channel (or the tRNS chunk data) after it's read, so that 0 is
1694 fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
1695 images) is fully transparent, with
1697 png_set_invert_alpha(png_ptr);
1699 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
1700 they can, resulting in, for example, 8 pixels per byte for 1 bit
1701 files. This code expands to 1 pixel per byte without changing the
1702 values of the pixels:
1705 png_set_packing(png_ptr);
1707 PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
1708 stored in a PNG image have been "scaled" or "shifted" up to the next
1709 higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
1710 8 bits/sample in the range [0, 255]). However, it is also possible to
1711 convert the PNG pixel data back to the original bit depth of the image.
1712 This call reduces the pixels back down to the original bit depth:
1714 png_color_8p sig_bit;
1716 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
1717 png_set_shift(png_ptr, sig_bit);
1719 PNG files store 3-color pixels in red, green, blue order. This code
1720 changes the storage of the pixels to blue, green, red:
1722 if (color_type == PNG_COLOR_TYPE_RGB ||
1723 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1724 png_set_bgr(png_ptr);
1726 PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
1727 into 4 or 8 bytes for windowing systems that need them in this format:
1729 if (color_type == PNG_COLOR_TYPE_RGB)
1730 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
1732 where "filler" is the 8 or 16-bit number to fill with, and the location is
1733 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
1734 you want the filler before the RGB or after. This transformation
1735 does not affect images that already have full alpha channels. To add an
1736 opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
1737 will generate RGBA pixels.
1739 Note that png_set_filler() does not change the color type. If you want
1740 to do that, you can add a true alpha channel with
1742 if (color_type == PNG_COLOR_TYPE_RGB ||
1743 color_type == PNG_COLOR_TYPE_GRAY)
1744 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
1746 where "filler" contains the alpha value to assign to each pixel.
1747 This function was added in libpng-1.2.7.
1749 If you are reading an image with an alpha channel, and you need the
1750 data as ARGB instead of the normal PNG format RGBA:
1752 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1753 png_set_swap_alpha(png_ptr);
1755 For some uses, you may want a grayscale image to be represented as
1756 RGB. This code will do that conversion:
1758 if (color_type == PNG_COLOR_TYPE_GRAY ||
1759 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1760 png_set_gray_to_rgb(png_ptr);
1762 Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
1765 if (color_type == PNG_COLOR_TYPE_RGB ||
1766 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
1767 png_set_rgb_to_gray_fixed(png_ptr, error_action,
1768 int red_weight, int green_weight);
1770 error_action = 1: silently do the conversion
1771 error_action = 2: issue a warning if the original
1772 image has any pixel where
1773 red != green or red != blue
1774 error_action = 3: issue an error and abort the
1775 conversion if the original
1776 image has any pixel where
1777 red != green or red != blue
1779 red_weight: weight of red component times 100000
1780 green_weight: weight of green component times 100000
1781 If either weight is negative, default
1782 weights (21268, 71514) are used.
1784 If you have set error_action = 1 or 2, you can
1785 later check whether the image really was gray, after processing
1786 the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
1787 It will return a png_byte that is zero if the image was gray or
1788 1 if there were any non-gray pixels. bKGD and sBIT data
1789 will be silently converted to grayscale, using the green channel
1790 data, regardless of the error_action setting.
1792 With red_weight+green_weight<=100000,
1793 the normalized graylevel is computed:
1795 int rw = red_weight * 65536;
1796 int gw = green_weight * 65536;
1797 int bw = 65536 - (rw + gw);
1798 gray = (rw*red + gw*green + bw*blue)/65536;
1800 The default values approximate those recommended in the Charles
1801 Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
1802 Copyright (c) 1998-01-04 Charles Poynton <poynton at inforamp.net>
1804 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
1806 Libpng approximates this with
1808 Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
1810 which can be expressed with integers as
1812 Y = (6969 * R + 23434 * G + 2365 * B)/32768
1814 The calculation is done in a linear colorspace, if the image gamma
1817 If you have a grayscale and you are using png_set_expand_depth(),
1818 png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
1819 a higher bit-depth, you must either supply the background color as a gray
1820 value at the original file bit-depth (need_expand = 1) or else supply the
1821 background color as an RGB triplet at the final, expanded bit depth
1822 (need_expand = 0). Similarly, if you are reading a paletted image, you
1823 must either supply the background color as a palette index (need_expand = 1)
1824 or as an RGB triplet that may or may not be in the palette (need_expand = 0).
1826 png_color_16 my_background;
1827 png_color_16p image_background;
1829 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
1830 png_set_background(png_ptr, image_background,
1831 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
1833 png_set_background(png_ptr, &my_background,
1834 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
1836 The png_set_background() function tells libpng to composite images
1837 with alpha or simple transparency against the supplied background
1838 color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
1839 you may use this color, or supply another color more suitable for
1840 the current display (e.g., the background color from a web page). You
1841 need to tell libpng whether the color is in the gamma space of the
1842 display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
1843 (PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
1844 that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
1845 know why anyone would use this, but it's here).
1847 To properly display PNG images on any kind of system, the application needs
1848 to know what the display gamma is. Ideally, the user will know this, and
1849 the application will allow them to set it. One method of allowing the user
1850 to set the display gamma separately for each system is to check for a
1851 SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
1854 Note that display_gamma is the overall gamma correction required to produce
1855 pleasing results, which depends on the lighting conditions in the surrounding
1856 environment. In a dim or brightly lit room, no compensation other than
1857 the physical gamma exponent of the monitor is needed, while in a dark room
1858 a slightly smaller exponent is better.
1860 double gamma, screen_gamma;
1862 if (/* We have a user-defined screen
1865 screen_gamma = user_defined_screen_gamma;
1867 /* One way that applications can share the same
1868 screen gamma value */
1869 else if ((gamma_str = getenv("SCREEN_GAMMA"))
1872 screen_gamma = (double)atof(gamma_str);
1874 /* If we don't have another value */
1877 screen_gamma = 2.2; /* A good guess for a
1878 PC monitor in a bright office or a dim room */
1879 screen_gamma = 2.0; /* A good guess for a
1880 PC monitor in a dark room */
1881 screen_gamma = 1.7 or 1.0; /* A good
1882 guess for Mac systems */
1885 The png_set_gamma() function handles gamma transformations of the data.
1886 Pass both the file gamma and the current screen_gamma. If the file does
1887 not have a gamma value, you can pass one anyway if you have an idea what
1888 it is (usually 0.45455 is a good guess for GIF images on PCs). Note
1889 that file gammas are inverted from screen gammas. See the discussions
1890 on gamma in the PNG specification for an excellent description of what
1891 gamma is, and why all applications should support it. It is strongly
1892 recommended that PNG viewers support gamma correction.
1894 if (png_get_gAMA(png_ptr, info_ptr, &gamma))
1895 png_set_gamma(png_ptr, screen_gamma, gamma);
1897 png_set_gamma(png_ptr, screen_gamma, 0.45455);
1899 If you need to reduce an RGB file to a paletted file, or if a paletted
1900 file has more entries then will fit on your screen, png_set_dither()
1901 will do that. Note that this is a simple match dither that merely
1902 finds the closest color available. This should work fairly well with
1903 optimized palettes, and fairly badly with linear color cubes. If you
1904 pass a palette that is larger then maximum_colors, the file will
1905 reduce the number of colors in the palette so it will fit into
1906 maximum_colors. If there is a histogram, it will use it to make
1907 more intelligent choices when reducing the palette. If there is no
1908 histogram, it may not do as good a job.
1910 if (color_type & PNG_COLOR_MASK_COLOR)
1912 if (png_get_valid(png_ptr, info_ptr,
1915 png_uint_16p histogram = NULL;
1917 png_get_hIST(png_ptr, info_ptr,
1919 png_set_dither(png_ptr, palette, num_palette,
1920 max_screen_colors, histogram, 1);
1924 png_color std_color_cube[MAX_SCREEN_COLORS] =
1927 png_set_dither(png_ptr, std_color_cube,
1928 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
1933 PNG files describe monochrome as black being zero and white being one.
1934 The following code will reverse this (make black be one and white be
1937 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
1938 png_set_invert_mono(png_ptr);
1940 This function can also be used to invert grayscale and gray-alpha images:
1942 if (color_type == PNG_COLOR_TYPE_GRAY ||
1943 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
1944 png_set_invert_mono(png_ptr);
1946 PNG files store 16 bit pixels in network byte order (big-endian,
1947 ie. most significant bits first). This code changes the storage to the
1948 other way (little-endian, i.e. least significant bits first, the
1949 way PCs store them):
1951 if (bit_depth == 16)
1952 png_set_swap(png_ptr);
1954 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
1955 need to change the order the pixels are packed into bytes, you can use:
1958 png_set_packswap(png_ptr);
1960 Finally, you can write your own transformation function if none of
1961 the existing ones meets your needs. This is done by setting a callback
1964 png_set_read_user_transform_fn(png_ptr,
1967 You must supply the function
1969 void read_transform_fn(png_ptr ptr, row_info_ptr
1970 row_info, png_bytep data)
1972 See pngtest.c for a working example. Your function will be called
1973 after all of the other transformations have been processed.
1975 You can also set up a pointer to a user structure for use by your
1976 callback function, and you can inform libpng that your transform
1977 function will change the number of channels or bit depth with the
1980 png_set_user_transform_info(png_ptr, user_ptr,
1981 user_depth, user_channels);
1983 The user's application, not libpng, is responsible for allocating and
1984 freeing any memory required for the user structure.
1986 You can retrieve the pointer via the function
1987 png_get_user_transform_ptr(). For example:
1989 voidp read_user_transform_ptr =
1990 png_get_user_transform_ptr(png_ptr);
1992 The last thing to handle is interlacing; this is covered in detail below,
1993 but you must call the function here if you want libpng to handle expansion
1994 of the interlaced image.
1996 number_of_passes = png_set_interlace_handling(png_ptr);
1998 After setting the transformations, libpng can update your png_info
1999 structure to reflect any transformations you've requested with this
2000 call. This is most useful to update the info structure's rowbytes
2001 field so you can use it to allocate your image memory. This function
2002 will also update your palette with the correct screen_gamma and
2003 background if these have been given with the calls above.
2005 png_read_update_info(png_ptr, info_ptr);
2007 After you call png_read_update_info(), you can allocate any
2008 memory you need to hold the image. The row data is simply
2009 raw byte data for all forms of images. As the actual allocation
2010 varies among applications, no example will be given. If you
2011 are allocating one large chunk, you will need to build an
2012 array of pointers to each row, as it will be needed for some
2013 of the functions below.
2015 .SS Reading image data
2017 After you've allocated memory, you can read the image data.
2018 The simplest way to do this is in one function call. If you are
2019 allocating enough memory to hold the whole image, you can just
2020 call png_read_image() and libpng will read in all the image data
2021 and put it in the memory area supplied. You will need to pass in
2022 an array of pointers to each row.
2024 This function automatically handles interlacing, so you don't need
2025 to call png_set_interlace_handling() or call this function multiple
2026 times, or any of that other stuff necessary with png_read_rows().
2028 png_read_image(png_ptr, row_pointers);
2030 where row_pointers is:
2032 png_bytep row_pointers[height];
2034 You can point to void or char or whatever you use for pixels.
2036 If you don't want to read in the whole image at once, you can
2037 use png_read_rows() instead. If there is no interlacing (check
2038 interlace_type == PNG_INTERLACE_NONE), this is simple:
2040 png_read_rows(png_ptr, row_pointers, NULL,
2043 where row_pointers is the same as in the png_read_image() call.
2045 If you are doing this just one row at a time, you can do this with
2046 a single row_pointer instead of an array of row_pointers:
2048 png_bytep row_pointer = row;
2049 png_read_row(png_ptr, row_pointer, NULL);
2051 If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2052 get somewhat harder. The only current (PNG Specification version 1.2)
2053 interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
2054 is a somewhat complicated 2D interlace scheme, known as Adam7, that
2055 breaks down an image into seven smaller images of varying size, based
2058 libpng can fill out those images or it can give them to you "as is".
2059 If you want them filled out, there are two ways to do that. The one
2060 mentioned in the PNG specification is to expand each pixel to cover
2061 those pixels that have not been read yet (the "rectangle" method).
2062 This results in a blocky image for the first pass, which gradually
2063 smooths out as more pixels are read. The other method is the "sparkle"
2064 method, where pixels are drawn only in their final locations, with the
2065 rest of the image remaining whatever colors they were initialized to
2066 before the start of the read. The first method usually looks better,
2067 but tends to be slower, as there are more pixels to put in the rows.
2069 If you don't want libpng to handle the interlacing details, just call
2070 png_read_rows() seven times to read in all seven images. Each of the
2071 images is a valid image by itself, or they can all be combined on an
2072 8x8 grid to form a single image (although if you intend to combine them
2073 you would be far better off using the libpng interlace handling).
2075 The first pass will return an image 1/8 as wide as the entire image
2076 (every 8th column starting in column 0) and 1/8 as high as the original
2077 (every 8th row starting in row 0), the second will be 1/8 as wide
2078 (starting in column 4) and 1/8 as high (also starting in row 0). The
2079 third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
2080 1/8 as high (every 8th row starting in row 4), and the fourth pass will
2081 be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
2082 and every 4th row starting in row 0). The fifth pass will return an
2083 image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
2084 while the sixth pass will be 1/2 as wide and 1/2 as high as the original
2085 (starting in column 1 and row 0). The seventh and final pass will be as
2086 wide as the original, and 1/2 as high, containing all of the odd
2087 numbered scanlines. Phew!
2089 If you want libpng to expand the images, call this before calling
2090 png_start_read_image() or png_read_update_info():
2092 if (interlace_type == PNG_INTERLACE_ADAM7)
2094 = png_set_interlace_handling(png_ptr);
2096 This will return the number of passes needed. Currently, this
2097 is seven, but may change if another interlace type is added.
2098 This function can be called even if the file is not interlaced,
2099 where it will return one pass.
2101 If you are not going to display the image after each pass, but are
2102 going to wait until the entire image is read in, use the sparkle
2103 effect. This effect is faster and the end result of either method
2104 is exactly the same. If you are planning on displaying the image
2105 after each pass, the "rectangle" effect is generally considered the
2108 If you only want the "sparkle" effect, just call png_read_rows() as
2109 normal, with the third parameter NULL. Make sure you make pass over
2110 the image number_of_passes times, and you don't change the data in the
2111 rows between calls. You can change the locations of the data, just
2112 not the data. Each pass only writes the pixels appropriate for that
2113 pass, and assumes the data from previous passes is still valid.
2115 png_read_rows(png_ptr, row_pointers, NULL,
2118 If you only want the first effect (the rectangles), do the same as
2119 before except pass the row buffer in the third parameter, and leave
2120 the second parameter NULL.
2122 png_read_rows(png_ptr, NULL, row_pointers,
2125 .SS Finishing a sequential read
2127 After you are finished reading the image through the
2128 low-level interface, you can finish reading the file. If you are
2129 interested in comments or time, which may be stored either before or
2130 after the image data, you should pass the separate png_info struct if
2131 you want to keep the comments from before and after the image
2132 separate. If you are not interested, you can pass NULL.
2134 png_read_end(png_ptr, end_info);
2136 When you are done, you can free all memory allocated by libpng like this:
2138 png_destroy_read_struct(&png_ptr, &info_ptr,
2141 It is also possible to individually free the info_ptr members that
2142 point to libpng-allocated storage with the following function:
2144 png_free_data(png_ptr, info_ptr, mask, seq)
2145 mask - identifies data to be freed, a mask
2146 containing the bitwise OR of one or
2148 PNG_FREE_PLTE, PNG_FREE_TRNS,
2149 PNG_FREE_HIST, PNG_FREE_ICCP,
2150 PNG_FREE_PCAL, PNG_FREE_ROWS,
2151 PNG_FREE_SCAL, PNG_FREE_SPLT,
2152 PNG_FREE_TEXT, PNG_FREE_UNKN,
2153 or simply PNG_FREE_ALL
2154 seq - sequence number of item to be freed
2157 This function may be safely called when the relevant storage has
2158 already been freed, or has not yet been allocated, or was allocated
2159 by the user and not by libpng, and will in those
2160 cases do nothing. The "seq" parameter is ignored if only one item
2161 of the selected data type, such as PLTE, is allowed. If "seq" is not
2162 -1, and multiple items are allowed for the data type identified in
2163 the mask, such as text or sPLT, only the n'th item in the structure
2164 is freed, where n is "seq".
2166 The default behavior is only to free data that was allocated internally
2167 by libpng. This can be changed, so that libpng will not free the data,
2168 or so that it will free data that was allocated by the user with png_malloc()
2169 or png_zalloc() and passed in via a png_set_*() function, with
2171 png_data_freer(png_ptr, info_ptr, freer, mask)
2172 mask - which data elements are affected
2173 same choices as in png_free_data()
2175 PNG_DESTROY_WILL_FREE_DATA
2176 PNG_SET_WILL_FREE_DATA
2177 PNG_USER_WILL_FREE_DATA
2179 This function only affects data that has already been allocated.
2180 You can call this function after reading the PNG data but before calling
2181 any png_set_*() functions, to control whether the user or the png_set_*()
2182 function is responsible for freeing any existing data that might be present,
2183 and again after the png_set_*() functions to control whether the user
2184 or png_destroy_*() is supposed to free the data. When the user assumes
2185 responsibility for libpng-allocated data, the application must use
2186 png_free() to free it, and when the user transfers responsibility to libpng
2187 for data that the user has allocated, the user must have used png_malloc()
2188 or png_zalloc() to allocate it.
2190 If you allocated your row_pointers in a single block, as suggested above in
2191 the description of the high level read interface, you must not transfer
2192 responsibility for freeing it to the png_set_rows or png_read_destroy function,
2193 because they would also try to free the individual row_pointers[i].
2195 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2196 separately, do not transfer responsibility for freeing text_ptr to libpng,
2197 because when libpng fills a png_text structure it combines these members with
2198 the key member, and png_free_data() will free only text_ptr.key. Similarly,
2199 if you transfer responsibility for free'ing text_ptr from libpng to your
2200 application, your application must not separately free those members.
2202 The png_free_data() function will turn off the "valid" flag for anything
2203 it frees. If you need to turn the flag off for a chunk that was freed by your
2204 application instead of by libpng, you can use
2206 png_set_invalid(png_ptr, info_ptr, mask);
2207 mask - identifies the chunks to be made invalid,
2208 containing the bitwise OR of one or
2210 PNG_INFO_gAMA, PNG_INFO_sBIT,
2211 PNG_INFO_cHRM, PNG_INFO_PLTE,
2212 PNG_INFO_tRNS, PNG_INFO_bKGD,
2213 PNG_INFO_hIST, PNG_INFO_pHYs,
2214 PNG_INFO_oFFs, PNG_INFO_tIME,
2215 PNG_INFO_pCAL, PNG_INFO_sRGB,
2216 PNG_INFO_iCCP, PNG_INFO_sPLT,
2217 PNG_INFO_sCAL, PNG_INFO_IDAT
2219 For a more compact example of reading a PNG image, see the file example.c.
2221 .SS Reading PNG files progressively
2223 The progressive reader is slightly different then the non-progressive
2224 reader. Instead of calling png_read_info(), png_read_rows(), and
2225 png_read_end(), you make one call to png_process_data(), which calls
2226 callbacks when it has the info, a row, or the end of the image. You
2227 set up these callbacks with png_set_progressive_read_fn(). You don't
2228 have to worry about the input/output functions of libpng, as you are
2229 giving the library the data directly in png_process_data(). I will
2230 assume that you have read the section on reading PNG files above,
2231 so I will only highlight the differences (although I will show
2234 png_structp png_ptr;
2237 /* An example code fragment of how you would
2238 initialize the progressive reader in your
2241 initialize_png_reader()
2243 png_ptr = png_create_read_struct
2244 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2245 user_error_fn, user_warning_fn);
2248 info_ptr = png_create_info_struct(png_ptr);
2251 png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
2256 if (setjmp(png_jmpbuf(png_ptr)))
2258 png_destroy_read_struct(&png_ptr, &info_ptr,
2263 /* This one's new. You can provide functions
2264 to be called when the header info is valid,
2265 when each row is completed, and when the image
2266 is finished. If you aren't using all functions,
2267 you can specify NULL parameters. Even when all
2268 three functions are NULL, you need to call
2269 png_set_progressive_read_fn(). You can use
2270 any struct as the user_ptr (cast to a void pointer
2271 for the function call), and retrieve the pointer
2272 from inside the callbacks using the function
2274 png_get_progressive_ptr(png_ptr);
2276 which will return a void pointer, which you have
2277 to cast appropriately.
2279 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
2280 info_callback, row_callback, end_callback);
2285 /* A code fragment that you call as you receive blocks
2288 process_data(png_bytep buffer, png_uint_32 length)
2290 if (setjmp(png_jmpbuf(png_ptr)))
2292 png_destroy_read_struct(&png_ptr, &info_ptr,
2297 /* This one's new also. Simply give it a chunk
2298 of data from the file stream (in order, of
2299 course). On machines with segmented memory
2300 models machines, don't give it any more than
2301 64K. The library seems to run fine with sizes
2302 of 4K. Although you can give it much less if
2303 necessary (I assume you can give it chunks of
2304 1 byte, I haven't tried less then 256 bytes
2305 yet). When this function returns, you may
2306 want to display any rows that were generated
2307 in the row callback if you don't already do
2310 png_process_data(png_ptr, info_ptr, buffer, length);
2314 /* This function is called (as set by
2315 png_set_progressive_read_fn() above) when enough data
2316 has been supplied so all of the header has been
2320 info_callback(png_structp png_ptr, png_infop info)
2322 /* Do any setup here, including setting any of
2323 the transformations mentioned in the Reading
2324 PNG files section. For now, you _must_ call
2325 either png_start_read_image() or
2326 png_read_update_info() after all the
2327 transformations are set (even if you don't set
2328 any). You may start getting rows before
2329 png_process_data() returns, so this is your
2330 last chance to prepare for that.
2334 /* This function is called when each row of image
2337 row_callback(png_structp png_ptr, png_bytep new_row,
2338 png_uint_32 row_num, int pass)
2340 /* If the image is interlaced, and you turned
2341 on the interlace handler, this function will
2342 be called for every row in every pass. Some
2343 of these rows will not be changed from the
2344 previous pass. When the row is not changed,
2345 the new_row variable will be NULL. The rows
2346 and passes are called in order, so you don't
2347 really need the row_num and pass, but I'm
2348 supplying them because it may make your life
2351 For the non-NULL rows of interlaced images,
2352 you must call png_progressive_combine_row()
2353 passing in the row and the old row. You can
2354 call this function for NULL rows (it will just
2355 return) and for non-interlaced images (it just
2356 does the memcpy for you) if it will make the
2357 code easier. Thus, you can just do this for
2361 png_progressive_combine_row(png_ptr, old_row,
2364 /* where old_row is what was displayed for
2365 previously for the row. Note that the first
2366 pass (pass == 0, really) will completely cover
2367 the old row, so the rows do not have to be
2368 initialized. After the first pass (and only
2369 for interlaced images), you will have to pass
2370 the current row, and the function will combine
2371 the old row and the new row.
2376 end_callback(png_structp png_ptr, png_infop info)
2378 /* This function is called after the whole image
2379 has been read, including any chunks after the
2380 image (up to and including the IEND). You
2381 will usually have the same info chunk as you
2382 had in the header, although some data may have
2383 been added to the comments and time fields.
2385 Most people won't do much here, perhaps setting
2386 a flag that marks the image as finished.
2394 Much of this is very similar to reading. However, everything of
2395 importance is repeated here, so you won't have to constantly look
2396 back up in the reading section to understand writing.
2400 You will want to do the I/O initialization before you get into libpng,
2401 so if it doesn't work, you don't have anything to undo. If you are not
2402 using the standard I/O functions, you will need to replace them with
2403 custom writing functions. See the discussion under Customizing libpng.
2405 FILE *fp = fopen(file_name, "wb");
2411 Next, png_struct and png_info need to be allocated and initialized.
2412 As these can be both relatively large, you may not want to store these
2413 on the stack, unless you have stack space to spare. Of course, you
2414 will want to check if they return NULL. If you are also reading,
2415 you won't want to name your read structure and your write structure
2416 both "png_ptr"; you can call them anything you like, such as
2417 "read_ptr" and "write_ptr". Look at pngtest.c, for example.
2419 png_structp png_ptr = png_create_write_struct
2420 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2421 user_error_fn, user_warning_fn);
2425 png_infop info_ptr = png_create_info_struct(png_ptr);
2428 png_destroy_write_struct(&png_ptr,
2433 If you want to use your own memory allocation routines,
2434 define PNG_USER_MEM_SUPPORTED and use
2435 png_create_write_struct_2() instead of png_create_write_struct():
2437 png_structp png_ptr = png_create_write_struct_2
2438 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2439 user_error_fn, user_warning_fn, (png_voidp)
2440 user_mem_ptr, user_malloc_fn, user_free_fn);
2442 After you have these structures, you will need to set up the
2443 error handling. When libpng encounters an error, it expects to
2444 longjmp() back to your routine. Therefore, you will need to call
2445 setjmp() and pass the png_jmpbuf(png_ptr). If you
2446 write the file from different routines, you will need to update
2447 the png_jmpbuf(png_ptr) every time you enter a new routine that will
2448 call a png_*() function. See your documentation of setjmp/longjmp
2449 for your compiler for more information on setjmp/longjmp. See
2450 the discussion on libpng error handling in the Customizing Libpng
2451 section below for more information on the libpng error handling.
2453 if (setjmp(png_jmpbuf(png_ptr)))
2455 png_destroy_write_struct(&png_ptr, &info_ptr);
2462 If you would rather avoid the complexity of setjmp/longjmp issues,
2463 you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
2464 errors will result in a call to PNG_ABORT() which defaults to abort().
2466 Now you need to set up the output code. The default for libpng is to
2467 use the C function fwrite(). If you use this, you will need to pass a
2468 valid FILE * in the function png_init_io(). Be sure that the file is
2469 opened in binary mode. Again, if you wish to handle writing data in
2470 another way, see the discussion on libpng I/O handling in the Customizing
2471 Libpng section below.
2473 png_init_io(png_ptr, fp);
2475 If you are embedding your PNG into a datastream such as MNG, and don't
2476 want libpng to write the 8-byte signature, or if you have already
2477 written the signature in your application, use
2479 png_set_sig_bytes(png_ptr, 8);
2481 to inform libpng that it should not write a signature.
2485 At this point, you can set up a callback function that will be
2486 called after each row has been written, which you can use to control
2487 a progress meter or the like. It's demonstrated in pngtest.c.
2488 You must supply a function
2490 void write_row_callback(png_ptr, png_uint_32 row,
2493 /* put your code here */
2496 (You can give it another name that you like instead of "write_row_callback")
2498 To inform libpng about your function, use
2500 png_set_write_status_fn(png_ptr, write_row_callback);
2502 You now have the option of modifying how the compression library will
2503 run. The following functions are mainly for testing, but may be useful
2504 in some cases, like if you need to write PNG files extremely fast and
2505 are willing to give up some compression, or if you want to get the
2506 maximum possible compression at the expense of slower writing. If you
2507 have no special needs in this area, let the library do what it wants by
2508 not calling this function at all, as it has been tuned to deliver a good
2509 speed/compression ratio. The second parameter to png_set_filter() is
2510 the filter method, for which the only valid values are 0 (as of the
2511 July 1999 PNG specification, version 1.2) or 64 (if you are writing
2512 a PNG datastream that is to be embedded in a MNG datastream). The third
2513 parameter is a flag that indicates which filter type(s) are to be tested
2514 for each scanline. See the PNG specification for details on the specific filter
2518 /* turn on or off filtering, and/or choose
2519 specific filters. You can use either a single
2520 PNG_FILTER_VALUE_NAME or the bitwise OR of one
2521 or more PNG_FILTER_NAME masks. */
2522 png_set_filter(png_ptr, 0,
2523 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
2524 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
2525 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
2526 PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE |
2527 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
2531 wants to start and stop using particular filters during compression,
2532 it should start out with all of the filters (to ensure that the previous
2533 row of pixels will be stored in case it's needed later), and then add
2534 and remove them after the start of compression.
2536 If you are writing a PNG datastream that is to be embedded in a MNG
2537 datastream, the second parameter can be either 0 or 64.
2539 The png_set_compression_*() functions interface to the zlib compression
2540 library, and should mostly be ignored unless you really know what you are
2541 doing. The only generally useful call is png_set_compression_level()
2542 which changes how much time zlib spends on trying to compress the image
2543 data. See the Compression Library (zlib.h and algorithm.txt, distributed
2544 with zlib) for details on the compression levels.
2546 /* set the zlib compression level */
2547 png_set_compression_level(png_ptr,
2548 Z_BEST_COMPRESSION);
2550 /* set other zlib parameters */
2551 png_set_compression_mem_level(png_ptr, 8);
2552 png_set_compression_strategy(png_ptr,
2553 Z_DEFAULT_STRATEGY);
2554 png_set_compression_window_bits(png_ptr, 15);
2555 png_set_compression_method(png_ptr, 8);
2556 png_set_compression_buffer_size(png_ptr, 8192)
2558 extern PNG_EXPORT(void,png_set_zbuf_size)
2560 .SS Setting the contents of info for output
2562 You now need to fill in the png_info structure with all the data you
2563 wish to write before the actual image. Note that the only thing you
2564 are allowed to write after the image is the text chunks and the time
2565 chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
2566 the latest PNG specification for more information on that. If you
2567 wish to write them before the image, fill them in now, and flag that
2568 data as being valid. If you want to wait until after the data, don't
2569 fill them until png_write_end(). For all the fields in png_info and
2570 their data types, see png.h. For explanations of what the fields
2571 contain, see the PNG specification.
2573 Some of the more important parts of the png_info are:
2575 png_set_IHDR(png_ptr, info_ptr, width, height,
2576 bit_depth, color_type, interlace_type,
2577 compression_type, filter_method)
2578 width - holds the width of the image
2579 in pixels (up to 2^31).
2580 height - holds the height of the image
2581 in pixels (up to 2^31).
2582 bit_depth - holds the bit depth of one of the
2584 (valid values are 1, 2, 4, 8, 16
2585 and depend also on the
2586 color_type. See also significant
2588 color_type - describes which color/alpha
2589 channels are present.
2591 (bit depths 1, 2, 4, 8, 16)
2592 PNG_COLOR_TYPE_GRAY_ALPHA
2594 PNG_COLOR_TYPE_PALETTE
2595 (bit depths 1, 2, 4, 8)
2598 PNG_COLOR_TYPE_RGB_ALPHA
2601 PNG_COLOR_MASK_PALETTE
2602 PNG_COLOR_MASK_COLOR
2603 PNG_COLOR_MASK_ALPHA
2605 interlace_type - PNG_INTERLACE_NONE or
2607 compression_type - (must be
2608 PNG_COMPRESSION_TYPE_DEFAULT)
2609 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
2610 or, if you are writing a PNG to
2611 be embedded in a MNG datastream,
2613 PNG_INTRAPIXEL_DIFFERENCING)
2615 If you call png_set_IHDR(), the call must appear before any of the
2616 other png_set_*() functions, which might require access to some of
2617 the IHDR settings. The remaining png_set_*() functions can be called
2620 png_set_PLTE(png_ptr, info_ptr, palette,
2622 palette - the palette for the file
2623 (array of png_color)
2624 num_palette - number of entries in the palette
2626 png_set_gAMA(png_ptr, info_ptr, gamma);
2627 gamma - the gamma the image was created
2630 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
2631 srgb_intent - the rendering intent
2632 (PNG_INFO_sRGB) The presence of
2633 the sRGB chunk means that the pixel
2634 data is in the sRGB color space.
2635 This chunk also implies specific
2636 values of gAMA and cHRM. Rendering
2637 intent is the CSS-1 property that
2638 has been defined by the International
2640 (http://www.color.org).
2642 PNG_sRGB_INTENT_SATURATION,
2643 PNG_sRGB_INTENT_PERCEPTUAL,
2644 PNG_sRGB_INTENT_ABSOLUTE, or
2645 PNG_sRGB_INTENT_RELATIVE.
2648 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
2650 srgb_intent - the rendering intent
2651 (PNG_INFO_sRGB) The presence of the
2652 sRGB chunk means that the pixel
2653 data is in the sRGB color space.
2654 This function also causes gAMA and
2655 cHRM chunks with the specific values
2656 that are consistent with sRGB to be
2659 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
2661 name - The profile name.
2662 compression - The compression type; always
2663 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
2664 You may give NULL to this argument to
2666 profile - International Color Consortium color
2667 profile data. May contain NULs.
2668 proflen - length of profile data in bytes.
2670 png_set_sBIT(png_ptr, info_ptr, sig_bit);
2671 sig_bit - the number of significant bits for
2672 (PNG_INFO_sBIT) each of the gray, red,
2673 green, and blue channels, whichever are
2674 appropriate for the given color type
2677 png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
2679 trans - array of transparent entries for
2680 palette (PNG_INFO_tRNS)
2681 trans_values - graylevel or color sample values of
2682 the single transparent color for
2683 non-paletted images (PNG_INFO_tRNS)
2684 num_trans - number of transparent entries
2687 png_set_hIST(png_ptr, info_ptr, hist);
2689 hist - histogram of palette (array of
2692 png_set_tIME(png_ptr, info_ptr, mod_time);
2693 mod_time - time image was last modified
2696 png_set_bKGD(png_ptr, info_ptr, background);
2697 background - background color (PNG_VALID_bKGD)
2699 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
2700 text_ptr - array of png_text holding image
2702 text_ptr[i].compression - type of compression used
2703 on "text" PNG_TEXT_COMPRESSION_NONE
2704 PNG_TEXT_COMPRESSION_zTXt
2705 PNG_ITXT_COMPRESSION_NONE
2706 PNG_ITXT_COMPRESSION_zTXt
2707 text_ptr[i].key - keyword for comment. Must contain
2709 text_ptr[i].text - text comments for current
2710 keyword. Can be NULL or empty.
2711 text_ptr[i].text_length - length of text string,
2712 after decompression, 0 for iTXt
2713 text_ptr[i].itxt_length - length of itxt string,
2714 after decompression, 0 for tEXt/zTXt
2715 text_ptr[i].lang - language of comment (NULL or
2717 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
2718 or empty for unknown).
2719 num_text - number of comments
2721 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
2723 palette_ptr - array of png_sPLT_struct structures
2724 to be added to the list of palettes
2725 in the info structure.
2726 num_spalettes - number of palette structures to be
2729 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
2731 offset_x - positive offset from the left
2733 offset_y - positive offset from the top
2735 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2737 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
2739 res_x - pixels/unit physical resolution
2741 res_y - pixels/unit physical resolution
2743 unit_type - PNG_RESOLUTION_UNKNOWN,
2744 PNG_RESOLUTION_METER
2746 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
2747 unit - physical scale units (an integer)
2748 width - width of a pixel in physical scale units
2749 height - height of a pixel in physical scale units
2750 (width and height are doubles)
2752 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
2753 unit - physical scale units (an integer)
2754 width - width of a pixel in physical scale units
2755 height - height of a pixel in physical scale units
2756 (width and height are strings like "2.54")
2758 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
2760 unknowns - array of png_unknown_chunk
2761 structures holding unknown chunks
2762 unknowns[i].name - name of unknown chunk
2763 unknowns[i].data - data of unknown chunk
2764 unknowns[i].size - size of unknown chunk's data
2765 unknowns[i].location - position to write chunk in file
2766 0: do not write chunk
2767 PNG_HAVE_IHDR: before PLTE
2768 PNG_HAVE_PLTE: before IDAT
2769 PNG_AFTER_IDAT: after IDAT
2771 The "location" member is set automatically according to
2772 what part of the output file has already been written.
2773 You can change its value after calling png_set_unknown_chunks()
2774 as demonstrated in pngtest.c. Within each of the "locations",
2775 the chunks are sequenced according to their position in the
2776 structure (that is, the value of "i", which is the order in which
2777 the chunk was either read from the input file or defined with
2778 png_set_unknown_chunks).
2780 A quick word about text and num_text. text is an array of png_text
2781 structures. num_text is the number of valid structures in the array.
2782 Each png_text structure holds a language code, a keyword, a text value,
2783 and a compression type.
2785 The compression types have the same valid numbers as the compression
2786 types of the image data. Currently, the only valid number is zero.
2787 However, you can store text either compressed or uncompressed, unlike
2788 images, which always have to be compressed. So if you don't want the
2789 text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
2790 Because tEXt and zTXt chunks don't have a language field, if you
2791 specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
2792 any language code or translated keyword will not be written out.
2794 Until text gets around 1000 bytes, it is not worth compressing it.
2795 After the text has been written out to the file, the compression type
2796 is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
2797 so that it isn't written out again at the end (in case you are calling
2798 png_write_end() with the same struct.
2800 The keywords that are given in the PNG Specification are:
2802 Title Short (one line) title or
2804 Author Name of image's creator
2805 Description Description of image (possibly long)
2806 Copyright Copyright notice
2807 Creation Time Time of original image creation
2808 (usually RFC 1123 format, see below)
2809 Software Software used to create the image
2810 Disclaimer Legal disclaimer
2811 Warning Warning of nature of content
2812 Source Device used to create the image
2813 Comment Miscellaneous comment; conversion
2814 from other image format
2816 The keyword-text pairs work like this. Keywords should be short
2817 simple descriptions of what the comment is about. Some typical
2818 keywords are found in the PNG specification, as is some recommendations
2819 on keywords. You can repeat keywords in a file. You can even write
2820 some text before the image and some after. For example, you may want
2821 to put a description of the image before the image, but leave the
2822 disclaimer until after, so viewers working over modem connections
2823 don't have to wait for the disclaimer to go over the modem before
2824 they start seeing the image. Finally, keywords should be full
2825 words, not abbreviations. Keywords and text are in the ISO 8859-1
2826 (Latin-1) character set (a superset of regular ASCII) and can not
2827 contain NUL characters, and should not contain control or other
2828 unprintable characters. To make the comments widely readable, stick
2829 with basic ASCII, and avoid machine specific character set extensions
2830 like the IBM-PC character set. The keyword must be present, but
2831 you can leave off the text string on non-compressed pairs.
2832 Compressed pairs must have a text string, as only the text string
2833 is compressed anyway, so the compression would be meaningless.
2835 PNG supports modification time via the png_time structure. Two
2836 conversion routines are provided, png_convert_from_time_t() for
2837 time_t and png_convert_from_struct_tm() for struct tm. The
2838 time_t routine uses gmtime(). You don't have to use either of
2839 these, but if you wish to fill in the png_time structure directly,
2840 you should provide the time in universal time (GMT) if possible
2841 instead of your local time. Note that the year number is the full
2842 year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
2843 that months start with 1.
2845 If you want to store the time of the original image creation, you should
2846 use a plain tEXt chunk with the "Creation Time" keyword. This is
2847 necessary because the "creation time" of a PNG image is somewhat vague,
2848 depending on whether you mean the PNG file, the time the image was
2849 created in a non-PNG format, a still photo from which the image was
2850 scanned, or possibly the subject matter itself. In order to facilitate
2851 machine-readable dates, it is recommended that the "Creation Time"
2852 tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
2853 although this isn't a requirement. Unlike the tIME chunk, the
2854 "Creation Time" tEXt chunk is not expected to be automatically changed
2855 by the software. To facilitate the use of RFC 1123 dates, a function
2856 png_convert_to_rfc1123(png_timep) is provided to convert from PNG
2857 time to an RFC 1123 format string.
2859 .SS Writing unknown chunks
2861 You can use the png_set_unknown_chunks function to queue up chunks
2862 for writing. You give it a chunk name, raw data, and a size; that's
2863 all there is to it. The chunks will be written by the next following
2864 png_write_info_before_PLTE, png_write_info, or png_write_end function.
2865 Any chunks previously read into the info structure's unknown-chunk
2866 list will also be written out in a sequence that satisfies the PNG
2867 specification's ordering rules.
2869 .SS The high-level write interface
2871 At this point there are two ways to proceed; through the high-level
2872 write interface, or through a sequence of low-level write operations.
2873 You can use the high-level interface if your image data is present
2874 in the info structure. All defined output
2875 transformations are permitted, enabled by the following masks.
2877 PNG_TRANSFORM_IDENTITY No transformation
2878 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
2879 PNG_TRANSFORM_PACKSWAP Change order of packed
2881 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
2882 PNG_TRANSFORM_SHIFT Normalize pixels to the
2884 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
2886 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
2888 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
2890 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
2891 PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes.
2893 If you have valid image data in the info structure (you can use
2894 png_set_rows() to put image data in the info structure), simply do this:
2896 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
2898 where png_transforms is an integer containing the bitwise OR of some set of
2899 transformation flags. This call is equivalent to png_write_info(),
2900 followed the set of transformations indicated by the transform mask,
2901 then png_write_image(), and finally png_write_end().
2903 (The final parameter of this call is not yet used. Someday it might point
2904 to transformation parameters required by some future output transform.)
2906 You must use png_transforms and not call any png_set_transform() functions
2907 when you use png_write_png().
2909 .SS The low-level write interface
2911 If you are going the low-level route instead, you are now ready to
2912 write all the file information up to the actual image data. You do
2913 this with a call to png_write_info().
2915 png_write_info(png_ptr, info_ptr);
2917 Note that there is one transformation you may need to do before
2918 png_write_info(). In PNG files, the alpha channel in an image is the
2919 level of opacity. If your data is supplied as a level of
2920 transparency, you can invert the alpha channel before you write it, so
2921 that 0 is fully transparent and 255 (in 8-bit or paletted images) or
2922 65535 (in 16-bit images) is fully opaque, with
2924 png_set_invert_alpha(png_ptr);
2926 This must appear before png_write_info() instead of later with the
2927 other transformations because in the case of paletted images the tRNS
2928 chunk data has to be inverted before the tRNS chunk is written. If
2929 your image is not a paletted image, the tRNS data (which in such cases
2930 represents a single color to be rendered as transparent) won't need to
2931 be changed, and you can safely do this transformation after your
2932 png_write_info() call.
2934 If you need to write a private chunk that you want to appear before
2935 the PLTE chunk when PLTE is present, you can write the PNG info in
2936 two steps, and insert code to write your own chunk between them:
2938 png_write_info_before_PLTE(png_ptr, info_ptr);
2939 png_set_unknown_chunks(png_ptr, info_ptr, ...);
2940 png_write_info(png_ptr, info_ptr);
2942 After you've written the file information, you can set up the library
2943 to handle any special transformations of the image data. The various
2944 ways to transform the data will be described in the order that they
2945 should occur. This is important, as some of these change the color
2946 type and/or bit depth of the data, and some others only work on
2947 certain color types and bit depths. Even though each transformation
2948 checks to see if it has data that it can do something with, you should
2949 make sure to only enable a transformation if it will be valid for the
2950 data. For example, don't swap red and blue on grayscale data.
2952 PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
2953 the library to strip input data that has 4 or 8 bytes per pixel down
2954 to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
2957 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
2959 where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
2960 PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
2961 is stored XRGB or RGBX.
2963 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2964 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
2965 If the data is supplied at 1 pixel per byte, use this code, which will
2966 correctly pack the pixels into a single byte:
2968 png_set_packing(png_ptr);
2970 PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
2971 data is of another bit depth, you can write an sBIT chunk into the
2972 file so that decoders can recover the original data if desired.
2974 /* Set the true bit depth of the image data */
2975 if (color_type & PNG_COLOR_MASK_COLOR)
2977 sig_bit.red = true_bit_depth;
2978 sig_bit.green = true_bit_depth;
2979 sig_bit.blue = true_bit_depth;
2983 sig_bit.gray = true_bit_depth;
2985 if (color_type & PNG_COLOR_MASK_ALPHA)
2987 sig_bit.alpha = true_bit_depth;
2990 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
2992 If the data is stored in the row buffer in a bit depth other than
2993 one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
2994 this will scale the values to appear to be the correct bit depth as
2997 png_set_shift(png_ptr, &sig_bit);
2999 PNG files store 16 bit pixels in network byte order (big-endian,
3000 ie. most significant bits first). This code would be used if they are
3001 supplied the other way (little-endian, i.e. least significant bits
3002 first, the way PCs store them):
3005 png_set_swap(png_ptr);
3007 If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
3008 need to change the order the pixels are packed into bytes, you can use:
3011 png_set_packswap(png_ptr);
3013 PNG files store 3 color pixels in red, green, blue order. This code
3014 would be used if they are supplied as blue, green, red:
3016 png_set_bgr(png_ptr);
3018 PNG files describe monochrome as black being zero and white being
3019 one. This code would be used if the pixels are supplied with this reversed
3020 (black being one and white being zero):
3022 png_set_invert_mono(png_ptr);
3024 Finally, you can write your own transformation function if none of
3025 the existing ones meets your needs. This is done by setting a callback
3028 png_set_write_user_transform_fn(png_ptr,
3029 write_transform_fn);
3031 You must supply the function
3033 void write_transform_fn(png_ptr ptr, row_info_ptr
3034 row_info, png_bytep data)
3036 See pngtest.c for a working example. Your function will be called
3037 before any of the other transformations are processed.
3039 You can also set up a pointer to a user structure for use by your
3042 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
3044 The user_channels and user_depth parameters of this function are ignored
3045 when writing; you can set them to zero as shown.
3047 You can retrieve the pointer via the function png_get_user_transform_ptr().
3050 voidp write_user_transform_ptr =
3051 png_get_user_transform_ptr(png_ptr);
3053 It is possible to have libpng flush any pending output, either manually,
3054 or automatically after a certain number of lines have been written. To
3055 flush the output stream a single time call:
3057 png_write_flush(png_ptr);
3059 and to have libpng flush the output stream periodically after a certain
3060 number of scanlines have been written, call:
3062 png_set_flush(png_ptr, nrows);
3064 Note that the distance between rows is from the last time png_write_flush()
3065 was called, or the first row of the image if it has never been called.
3066 So if you write 50 lines, and then png_set_flush 25, it will flush the
3067 output on the next scanline, and every 25 lines thereafter, unless
3068 png_write_flush() is called before 25 more lines have been written.
3069 If nrows is too small (less than about 10 lines for a 640 pixel wide
3070 RGB image) the image compression may decrease noticeably (although this
3071 may be acceptable for real-time applications). Infrequent flushing will
3072 only degrade the compression performance by a few percent over images
3073 that do not use flushing.
3075 .SS Writing the image data
3077 That's it for the transformations. Now you can write the image data.
3078 The simplest way to do this is in one function call. If you have the
3079 whole image in memory, you can just call png_write_image() and libpng
3080 will write the image. You will need to pass in an array of pointers to
3081 each row. This function automatically handles interlacing, so you don't
3082 need to call png_set_interlace_handling() or call this function multiple
3083 times, or any of that other stuff necessary with png_write_rows().
3085 png_write_image(png_ptr, row_pointers);
3087 where row_pointers is:
3089 png_byte *row_pointers[height];
3091 You can point to void or char or whatever you use for pixels.
3093 If you don't want to write the whole image at once, you can
3094 use png_write_rows() instead. If the file is not interlaced,
3097 png_write_rows(png_ptr, row_pointers,
3100 row_pointers is the same as in the png_write_image() call.
3102 If you are just writing one row at a time, you can do this with
3103 a single row_pointer instead of an array of row_pointers:
3105 png_bytep row_pointer = row;
3107 png_write_row(png_ptr, row_pointer);
3109 When the file is interlaced, things can get a good deal more
3110 complicated. The only currently (as of the PNG Specification
3111 version 1.2, dated July 1999) defined interlacing scheme for PNG files
3112 is the "Adam7" interlace scheme, that breaks down an
3113 image into seven smaller images of varying size. libpng will build
3114 these images for you, or you can do them yourself. If you want to
3115 build them yourself, see the PNG specification for details of which
3116 pixels to write when.
3118 If you don't want libpng to handle the interlacing details, just
3119 use png_set_interlace_handling() and call png_write_rows() the
3120 correct number of times to write all seven sub-images.
3122 If you want libpng to build the sub-images, call this before you start
3126 png_set_interlace_handling(png_ptr);
3128 This will return the number of passes needed. Currently, this
3129 is seven, but may change if another interlace type is added.
3131 Then write the complete image number_of_passes times.
3133 png_write_rows(png_ptr, row_pointers,
3136 As some of these rows are not used, and thus return immediately,
3137 you may want to read about interlacing in the PNG specification,
3138 and only update the rows that are actually used.
3140 .SS Finishing a sequential write
3142 After you are finished writing the image, you should finish writing
3143 the file. If you are interested in writing comments or time, you should
3144 pass an appropriately filled png_info pointer. If you are not interested,
3147 png_write_end(png_ptr, info_ptr);
3149 When you are done, you can free all memory used by libpng like this:
3151 png_destroy_write_struct(&png_ptr, &info_ptr);
3153 It is also possible to individually free the info_ptr members that
3154 point to libpng-allocated storage with the following function:
3156 png_free_data(png_ptr, info_ptr, mask, seq)
3157 mask - identifies data to be freed, a mask
3158 containing the bitwise OR of one or
3160 PNG_FREE_PLTE, PNG_FREE_TRNS,
3161 PNG_FREE_HIST, PNG_FREE_ICCP,
3162 PNG_FREE_PCAL, PNG_FREE_ROWS,
3163 PNG_FREE_SCAL, PNG_FREE_SPLT,
3164 PNG_FREE_TEXT, PNG_FREE_UNKN,
3165 or simply PNG_FREE_ALL
3166 seq - sequence number of item to be freed
3169 This function may be safely called when the relevant storage has
3170 already been freed, or has not yet been allocated, or was allocated
3171 by the user and not by libpng, and will in those
3172 cases do nothing. The "seq" parameter is ignored if only one item
3173 of the selected data type, such as PLTE, is allowed. If "seq" is not
3174 -1, and multiple items are allowed for the data type identified in
3175 the mask, such as text or sPLT, only the n'th item in the structure
3176 is freed, where n is "seq".
3178 If you allocated data such as a palette that you passed
3179 in to libpng with png_set_*, you must not free it until just before the call to
3180 png_destroy_write_struct().
3182 The default behavior is only to free data that was allocated internally
3183 by libpng. This can be changed, so that libpng will not free the data,
3184 or so that it will free data that was allocated by the user with png_malloc()
3185 or png_zalloc() and passed in via a png_set_*() function, with
3187 png_data_freer(png_ptr, info_ptr, freer, mask)
3188 mask - which data elements are affected
3189 same choices as in png_free_data()
3191 PNG_DESTROY_WILL_FREE_DATA
3192 PNG_SET_WILL_FREE_DATA
3193 PNG_USER_WILL_FREE_DATA
3195 For example, to transfer responsibility for some data from a read structure
3196 to a write structure, you could use
3198 png_data_freer(read_ptr, read_info_ptr,
3199 PNG_USER_WILL_FREE_DATA,
3200 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3201 png_data_freer(write_ptr, write_info_ptr,
3202 PNG_DESTROY_WILL_FREE_DATA,
3203 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
3205 thereby briefly reassigning responsibility for freeing to the user but
3206 immediately afterwards reassigning it once more to the write_destroy
3207 function. Having done this, it would then be safe to destroy the read
3208 structure and continue to use the PLTE, tRNS, and hIST data in the write
3211 This function only affects data that has already been allocated.
3212 You can call this function before calling after the png_set_*() functions
3213 to control whether the user or png_destroy_*() is supposed to free the data.
3214 When the user assumes responsibility for libpng-allocated data, the
3215 application must use
3216 png_free() to free it, and when the user transfers responsibility to libpng
3217 for data that the user has allocated, the user must have used png_malloc()
3218 or png_zalloc() to allocate it.
3220 If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
3221 separately, do not transfer responsibility for freeing text_ptr to libpng,
3222 because when libpng fills a png_text structure it combines these members with
3223 the key member, and png_free_data() will free only text_ptr.key. Similarly,
3224 if you transfer responsibility for free'ing text_ptr from libpng to your
3225 application, your application must not separately free those members.
3226 For a more compact example of writing a PNG image, see the file example.c.
3228 .SH V. Modifying/Customizing libpng:
3230 There are two issues here. The first is changing how libpng does
3231 standard things like memory allocation, input/output, and error handling.
3232 The second deals with more complicated things like adding new chunks,
3233 adding new transformations, and generally changing how libpng works.
3234 Both of those are compile-time issues; that is, they are generally
3235 determined at the time the code is written, and there is rarely a need
3236 to provide the user with a means of changing them.
3238 Memory allocation, input/output, and error handling
3240 All of the memory allocation, input/output, and error handling in libpng
3241 goes through callbacks that are user-settable. The default routines are
3242 in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
3243 these functions, call the appropriate png_set_*_fn() function.
3245 Memory allocation is done through the functions png_malloc()
3246 and png_free(). These currently just call the standard C functions. If
3247 your pointers can't access more then 64K at a time, you will want to set
3248 MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
3249 memory allocation on a platform will change between applications, these
3250 functions must be modified in the library at compile time. If you prefer
3251 to use a different method of allocating and freeing data, you can use
3252 png_create_read_struct_2() or png_create_write_struct_2() to register
3253 your own functions as described above.
3254 These functions also provide a void pointer that can be retrieved via
3256 mem_ptr=png_get_mem_ptr(png_ptr);
3258 Your replacement memory functions must have prototypes as follows:
3260 png_voidp malloc_fn(png_structp png_ptr,
3262 void free_fn(png_structp png_ptr, png_voidp ptr);
3264 Your malloc_fn() must return NULL in case of failure. The png_malloc()
3265 function will normally call png_error() if it receives a NULL from the
3266 system memory allocator or from your replacement malloc_fn().
3268 Your free_fn() will never be called with a NULL ptr, since libpng's
3269 png_free() checks for NULL before calling free_fn().
3271 Input/Output in libpng is done through png_read() and png_write(),
3272 which currently just call fread() and fwrite(). The FILE * is stored in
3273 png_struct and is initialized via png_init_io(). If you wish to change
3274 the method of I/O, the library supplies callbacks that you can set
3275 through the function png_set_read_fn() and png_set_write_fn() at run
3276 time, instead of calling the png_init_io() function. These functions
3277 also provide a void pointer that can be retrieved via the function
3278 png_get_io_ptr(). For example:
3280 png_set_read_fn(png_structp read_ptr,
3281 voidp read_io_ptr, png_rw_ptr read_data_fn)
3283 png_set_write_fn(png_structp write_ptr,
3284 voidp write_io_ptr, png_rw_ptr write_data_fn,
3285 png_flush_ptr output_flush_fn);
3287 voidp read_io_ptr = png_get_io_ptr(read_ptr);
3288 voidp write_io_ptr = png_get_io_ptr(write_ptr);
3290 The replacement I/O functions must have prototypes as follows:
3292 void user_read_data(png_structp png_ptr,
3293 png_bytep data, png_size_t length);
3294 void user_write_data(png_structp png_ptr,
3295 png_bytep data, png_size_t length);
3296 void user_flush_data(png_structp png_ptr);
3298 Supplying NULL for the read, write, or flush functions sets them back
3299 to using the default C stream functions. It is an error to read from
3300 a write stream, and vice versa.
3302 Error handling in libpng is done through png_error() and png_warning().
3303 Errors handled through png_error() are fatal, meaning that png_error()
3304 should never return to its caller. Currently, this is handled via
3305 setjmp() and longjmp() (unless you have compiled libpng with
3306 PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
3307 but you could change this to do things like exit() if you should wish.
3309 On non-fatal errors, png_warning() is called
3310 to print a warning message, and then control returns to the calling code.
3311 By default png_error() and png_warning() print a message on stderr via
3312 fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
3313 (because you don't want the messages) or PNG_NO_STDIO defined (because
3314 fprintf() isn't available). If you wish to change the behavior of the error
3315 functions, you will need to set up your own message callbacks. These
3316 functions are normally supplied at the time that the png_struct is created.
3317 It is also possible to redirect errors and warnings to your own replacement
3318 functions after png_create_*_struct() has been called by calling:
3320 png_set_error_fn(png_structp png_ptr,
3321 png_voidp error_ptr, png_error_ptr error_fn,
3322 png_error_ptr warning_fn);
3324 png_voidp error_ptr = png_get_error_ptr(png_ptr);
3326 If NULL is supplied for either error_fn or warning_fn, then the libpng
3327 default function will be used, calling fprintf() and/or longjmp() if a
3328 problem is encountered. The replacement error functions should have
3329 parameters as follows:
3331 void user_error_fn(png_structp png_ptr,
3332 png_const_charp error_msg);
3333 void user_warning_fn(png_structp png_ptr,
3334 png_const_charp warning_msg);
3336 The motivation behind using setjmp() and longjmp() is the C++ throw and
3337 catch exception handling methods. This makes the code much easier to write,
3338 as there is no need to check every return code of every function call.
3339 However, there are some uncertainties about the status of local variables
3340 after a longjmp, so the user may want to be careful about doing anything after
3341 setjmp returns non-zero besides returning itself. Consult your compiler
3342 documentation for more details. For an alternative approach, you may wish
3343 to use the "cexcept" facility (see http://cexcept.sourceforge.net).
3347 If you need to read or write custom chunks, you may need to get deeper
3348 into the libpng code. The library now has mechanisms for storing
3349 and writing chunks of unknown type; you can even declare callbacks
3350 for custom chunks. However, this may not be good enough if the
3351 library code itself needs to know about interactions between your
3352 chunk and existing `intrinsic' chunks.
3354 If you need to write a new intrinsic chunk, first read the PNG
3355 specification. Acquire a first level of
3356 understanding of how it works. Pay particular attention to the
3357 sections that describe chunk names, and look at how other chunks were
3358 designed, so you can do things similarly. Second, check out the
3359 sections of libpng that read and write chunks. Try to find a chunk
3360 that is similar to yours and use it as a template. More details can
3361 be found in the comments inside the code. It is best to handle unknown
3362 chunks in a generic method, via callback functions, instead of by
3363 modifying libpng functions.
3365 If you wish to write your own transformation for the data, look through
3366 the part of the code that does the transformations, and check out some of
3367 the simpler ones to get an idea of how they work. Try to find a similar
3368 transformation to the one you want to add and copy off of it. More details
3369 can be found in the comments inside the code itself.
3371 .SS Configuring for 16 bit platforms
3373 You will want to look into zconf.h to tell zlib (and thus libpng) that
3374 it cannot allocate more then 64K at a time. Even if you can, the memory
3375 won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
3377 .SS Configuring for DOS
3379 For DOS users who only have access to the lower 640K, you will
3380 have to limit zlib's memory usage via a png_set_compression_mem_level()
3381 call. See zlib.h or zconf.h in the zlib library for more information.
3383 .SS Configuring for Medium Model
3385 Libpng's support for medium model has been tested on most of the popular
3386 compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
3387 defined, and FAR gets defined to far in pngconf.h, and you should be
3388 all set. Everything in the library (except for zlib's structure) is
3389 expecting far data. You must use the typedefs with the p or pp on
3390 the end for pointers (or at least look at them and be careful). Make
3391 note that the rows of data are defined as png_bytepp, which is an
3392 unsigned char far * far *.
3394 .SS Configuring for gui/windowing platforms:
3396 You will need to write new error and warning functions that use the GUI
3397 interface, as described previously, and set them to be the error and
3398 warning functions at the time that png_create_*_struct() is called,
3399 in order to have them available during the structure initialization.
3400 They can be changed later via png_set_error_fn(). On some compilers,
3401 you may also have to change the memory allocators (png_malloc, etc.).
3403 .SS Configuring for compiler xxx:
3405 All includes for libpng are in pngconf.h. If you need to add/change/delete
3406 an include, this is the place to do it. The includes that are not
3407 needed outside libpng are protected by the PNG_INTERNAL definition,
3408 which is only defined for those routines inside libpng itself. The
3409 files in libpng proper only include png.h, which includes pngconf.h.
3411 .SS Configuring zlib:
3413 There are special functions to configure the compression. Perhaps the
3414 most useful one changes the compression level, which currently uses
3415 input compression values in the range 0 - 9. The library normally
3416 uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
3417 have shown that for a large majority of images, compression values in
3418 the range 3-6 compress nearly as well as higher levels, and do so much
3419 faster. For online applications it may be desirable to have maximum speed
3420 (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
3421 specify no compression (Z_NO_COMPRESSION = 0), but this would create
3422 files larger than just storing the raw bitmap. You can specify the
3423 compression level by calling:
3425 png_set_compression_level(png_ptr, level);
3427 Another useful one is to reduce the memory level used by the library.
3428 The memory level defaults to 8, but it can be lowered if you are
3429 short on memory (running DOS, for example, where you only have 640K).
3430 Note that the memory level does have an effect on compression; among
3431 other things, lower levels will result in sections of incompressible
3432 data being emitted in smaller stored blocks, with a correspondingly
3433 larger relative overhead of up to 15% in the worst case.
3435 png_set_compression_mem_level(png_ptr, level);
3437 The other functions are for configuring zlib. They are not recommended
3438 for normal use and may result in writing an invalid PNG file. See
3439 zlib.h for more information on what these mean.
3441 png_set_compression_strategy(png_ptr,
3443 png_set_compression_window_bits(png_ptr,
3445 png_set_compression_method(png_ptr, method);
3446 png_set_compression_buffer_size(png_ptr, size);
3448 .SS Controlling row filtering
3450 If you want to control whether libpng uses filtering or not, which
3451 filters are used, and how it goes about picking row filters, you
3452 can call one of these functions. The selection and configuration
3453 of row filters can have a significant impact on the size and
3454 encoding speed and a somewhat lesser impact on the decoding speed
3455 of an image. Filtering is enabled by default for RGB and grayscale
3456 images (with and without alpha), but not for paletted images nor
3457 for any images with bit depths less than 8 bits/pixel.
3459 The 'method' parameter sets the main filtering method, which is
3460 currently only '0' in the PNG 1.2 specification. The 'filters'
3461 parameter sets which filter(s), if any, should be used for each
3462 scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
3463 to turn filtering on and off, respectively.
3465 Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
3466 PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
3467 ORed together with '|' to specify one or more filters to use.
3468 These filters are described in more detail in the PNG specification.
3469 If you intend to change the filter type during the course of writing
3470 the image, you should start with flags set for all of the filters
3471 you intend to use so that libpng can initialize its internal
3472 structures appropriately for all of the filter types. (Note that this
3473 means the first row must always be adaptively filtered, because libpng
3474 currently does not allocate the filter buffers until png_write_row()
3475 is called for the first time.)
3477 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
3478 PNG_FILTER_UP | PNG_FILTER_AVE |
3479 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
3481 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
3483 The second parameter can also be
3484 PNG_INTRAPIXEL_DIFFERENCING if you are
3485 writing a PNG to be embedded in a MNG
3486 datastream. This parameter must be the
3487 same as the value of filter_method used
3490 It is also possible to influence how libpng chooses from among the
3491 available filters. This is done in one or both of two ways - by
3492 telling it how important it is to keep the same filter for successive
3493 rows, and by telling it the relative computational costs of the filters.
3495 double weights[3] = {1.5, 1.3, 1.1},
3496 costs[PNG_FILTER_VALUE_LAST] =
3497 {1.0, 1.3, 1.3, 1.5, 1.7};
3499 png_set_filter_heuristics(png_ptr,
3500 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
3503 The weights are multiplying factors that indicate to libpng that the
3504 row filter should be the same for successive rows unless another row filter
3505 is that many times better than the previous filter. In the above example,
3506 if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
3507 "sum of absolute differences" 1.5 x 1.3 times higher than other filters
3508 and still be chosen, while the NONE filter could have a sum 1.1 times
3509 higher than other filters and still be chosen. Unspecified weights are
3510 taken to be 1.0, and the specified weights should probably be declining
3511 like those above in order to emphasize recent filters over older filters.
3513 The filter costs specify for each filter type a relative decoding cost
3514 to be considered when selecting row filters. This means that filters
3515 with higher costs are less likely to be chosen over filters with lower
3516 costs, unless their "sum of absolute differences" is that much smaller.
3517 The costs do not necessarily reflect the exact computational speeds of
3518 the various filters, since this would unduly influence the final image
3521 Note that the numbers above were invented purely for this example and
3522 are given only to help explain the function usage. Little testing has
3523 been done to find optimum values for either the costs or the weights.
3525 .SS Removing unwanted object code
3527 There are a bunch of #define's in pngconf.h that control what parts of
3528 libpng are compiled. All the defines end in _SUPPORTED. If you are
3529 never going to use a capability, you can change the #define to #undef
3530 before recompiling libpng and save yourself code and data space, or
3531 you can turn off individual capabilities with defines that begin with
3534 You can also turn all of the transforms and ancillary chunk capabilities
3535 off en masse with compiler directives that define
3536 PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
3538 along with directives to turn on any of the capabilities that you do
3539 want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
3540 the extra transformations but still leave the library fully capable of reading
3541 and writing PNG files with all known public chunks
3542 Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
3543 produces a library that is incapable of reading or writing ancillary chunks.
3544 If you are not using the progressive reading capability, you can
3545 turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
3546 this with the INTERLACING capability, which you'll still have).
3548 All the reading and writing specific code are in separate files, so the
3549 linker should only grab the files it needs. However, if you want to
3550 make sure, or if you are building a stand alone library, all the
3551 reading files start with pngr and all the writing files start with
3552 pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
3553 are used for both reading and writing, and always need to be included.
3554 The progressive reader is in pngpread.c
3556 If you are creating or distributing a dynamically linked library (a .so
3557 or DLL file), you should not remove or disable any parts of the library,
3558 as this will cause applications linked with different versions of the
3559 library to fail if they call functions not available in your library.
3560 The size of the library itself should not be an issue, because only
3561 those sections that are actually used will be loaded into memory.
3563 .SS Requesting debug printout
3565 The macro definition PNG_DEBUG can be used to request debugging
3566 printout. Set it to an integer value in the range 0 to 3. Higher
3567 numbers result in increasing amounts of debugging information. The
3568 information is printed to the "stderr" file, unless another file
3569 name is specified in the PNG_DEBUG_FILE macro definition.
3571 When PNG_DEBUG > 0, the following functions (macros) become available:
3573 png_debug(level, message)
3574 png_debug1(level, message, p1)
3575 png_debug2(level, message, p1, p2)
3577 in which "level" is compared to PNG_DEBUG to decide whether to print
3578 the message, "message" is the formatted string to be printed,
3579 and p1 and p2 are parameters that are to be embedded in the string
3580 according to printf-style formatting directives. For example,
3582 png_debug1(2, "foo=%d\n", foo);
3587 fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
3589 When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
3590 can still use PNG_DEBUG to control your own debugging:
3596 When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
3597 having level = 0 will be printed. There aren't any such statements in
3598 this version of libpng, but if you insert some they will be printed.
3600 .SH VII. MNG support
3602 The MNG specification (available at http://www.libpng.org/pub/mng) allows
3603 certain extensions to PNG for PNG images that are embedded in MNG datastreams.
3604 Libpng can support some of these extensions. To enable them, use the
3605 png_permit_mng_features() function:
3607 feature_set = png_permit_mng_features(png_ptr, mask)
3608 mask is a png_uint_32 containing the bitwise OR of the
3609 features you want to enable. These include
3610 PNG_FLAG_MNG_EMPTY_PLTE
3611 PNG_FLAG_MNG_FILTER_64
3612 PNG_ALL_MNG_FEATURES
3613 feature_set is a png_uint_32 that is the bitwise AND of
3614 your mask with the set of MNG features that is
3615 supported by the version of libpng that you are using.
3617 It is an error to use this function when reading or writing a standalone
3618 PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
3619 in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
3620 and the MHDR and MEND chunks. Libpng does not provide support for these
3621 or any other MNG chunks; your application must provide its own support for
3622 them. You may wish to consider using libmng (available at
3623 http://www.libmng.com) instead.
3625 .SH VIII. Changes to Libpng from version 0.88
3627 It should be noted that versions of libpng later than 0.96 are not
3628 distributed by the original libpng author, Guy Schalnat, nor by
3629 Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
3630 distributed versions 0.89 through 0.96, but rather by another member
3631 of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
3632 still alive and well, but they have moved on to other things.
3634 The old libpng functions png_read_init(), png_write_init(),
3635 png_info_init(), png_read_destroy(), and png_write_destroy() have been
3636 moved to PNG_INTERNAL in version 0.95 to discourage their use. These
3637 functions will be removed from libpng version 2.0.0.
3639 The preferred method of creating and initializing the libpng structures is
3640 via the png_create_read_struct(), png_create_write_struct(), and
3641 png_create_info_struct() because they isolate the size of the structures
3642 from the application, allow version error checking, and also allow the
3643 use of custom error handling routines during the initialization, which
3644 the old functions do not. The functions png_read_destroy() and
3645 png_write_destroy() do not actually free the memory that libpng
3646 allocated for these structs, but just reset the data structures, so they
3647 can be used instead of png_destroy_read_struct() and
3648 png_destroy_write_struct() if you feel there is too much system overhead
3649 allocating and freeing the png_struct for each image read.
3651 Setting the error callbacks via png_set_message_fn() before
3652 png_read_init() as was suggested in libpng-0.88 is no longer supported
3653 because this caused applications that do not use custom error functions
3654 to fail if the png_ptr was not initialized to zero. It is still possible
3655 to set the error callbacks AFTER png_read_init(), or to change them with
3656 png_set_error_fn(), which is essentially the same function, but with a new
3657 name to force compilation errors with applications that try to use the old
3660 Starting with version 1.0.7, you can find out which version of the library
3661 you are using at run-time:
3663 png_uint_32 libpng_vn = png_access_version_number();
3665 The number libpng_vn is constructed from the major version, minor
3666 version with leading zero, and release number with leading zero,
3667 (e.g., libpng_vn for version 1.0.7 is 10007).
3669 You can also check which version of png.h you used when compiling your
3672 png_uint_32 application_vn = PNG_LIBPNG_VER;
3674 .SH IX. Y2K Compliance in libpng
3678 Since the PNG Development group is an ad-hoc body, we can't make
3679 an official declaration.
3681 This is your unofficial assurance that libpng from version 0.71 and
3682 upward through 1.2.34 are Y2K compliant. It is my belief that earlier
3683 versions were also Y2K compliant.
3685 Libpng only has three year fields. One is a 2-byte unsigned integer that
3686 will hold years up to 65535. The other two hold the date in text
3687 format, and will hold years up to 9999.
3690 "png_uint_16 year" in png_time_struct.
3693 "png_charp time_buffer" in png_struct and
3694 "near_time_buffer", which is a local character string in png.c.
3696 There are seven time-related functions:
3698 png_convert_to_rfc_1123() in png.c
3699 (formerly png_convert_to_rfc_1152() in error)
3700 png_convert_from_struct_tm() in pngwrite.c, called
3702 png_convert_from_time_t() in pngwrite.c
3703 png_get_tIME() in pngget.c
3704 png_handle_tIME() in pngrutil.c, called in pngread.c
3705 png_set_tIME() in pngset.c
3706 png_write_tIME() in pngwutil.c, called in pngwrite.c
3708 All appear to handle dates properly in a Y2K environment. The
3709 png_convert_from_time_t() function calls gmtime() to convert from system
3710 clock time, which returns (year - 1900), which we properly convert to
3711 the full 4-digit year. There is a possibility that applications using
3712 libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
3713 function, or that they are incorrectly passing only a 2-digit year
3714 instead of "year - 1900" into the png_convert_from_struct_tm() function,
3715 but this is not under our control. The libpng documentation has always
3716 stated that it works with 4-digit years, and the APIs have been
3719 The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
3720 integer to hold the year, and can hold years as large as 65535.
3722 zlib, upon which libpng depends, is also Y2K compliant. It contains
3723 no date-related code.
3726 Glenn Randers-Pehrson
3728 PNG Development Group
3732 Note about libpng version numbers:
3734 Due to various miscommunications, unforeseen code incompatibilities
3735 and occasional factors outside the authors' control, version numbering
3736 on the library has not always been consistent and straightforward.
3737 The following table summarizes matters since version 0.89c, which was
3738 the first widely used release:
3740 source png.h png.h shared-lib
3741 version string int version
3742 ------- ------ ----- ----------
3743 0.89c ("beta 3") 0.89 89 1.0.89
3744 0.90 ("beta 4") 0.90 90 0.90
3745 0.95 ("beta 5") 0.95 95 0.95
3746 0.96 ("beta 6") 0.96 96 0.96
3747 0.97b ("beta 7") 1.00.97 97 1.0.1
3748 0.97c 0.97 97 2.0.97
3751 0.99a-m 0.99 99 2.0.99
3753 1.0.0 1.0.0 100 2.1.0
3754 1.0.0 (from here on, the 100 2.1.0
3755 1.0.1 png.h string is 10001 2.1.0
3756 1.0.1a-e identical to the 10002 from here on, the
3757 1.0.2 source version) 10002 shared library is 2.V
3758 1.0.2a-b 10003 where V is the source
3759 1.0.1 10001 code version except as
3760 1.0.1a-e 10002 2.1.0.1a-e noted.
3762 1.0.2a-b 10003 2.1.0.2a-b
3764 1.0.3a-d 10004 2.1.0.3a-d
3766 1.0.4a-f 10005 2.1.0.4a-f
3767 1.0.5 (+ 2 patches) 10005 2.1.0.5
3768 1.0.5a-d 10006 2.1.0.5a-d
3769 1.0.5e-r 10100 2.1.0.5e-r
3770 1.0.5s-v 10006 2.1.0.5s-v
3771 1.0.6 (+ 3 patches) 10006 2.1.0.6
3772 1.0.6d-g 10007 2.1.0.6d-g
3775 1.0.6j 10007 2.1.0.6j
3776 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
3777 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
3778 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
3779 1.0.7 1 10007 2.1.0.7
3780 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
3781 1.0.8rc1 1 10008 2.1.0.8rc1
3782 1.0.8 1 10008 2.1.0.8
3783 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
3784 1.0.9rc1 1 10009 2.1.0.9rc1
3785 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
3786 1.0.9rc2 1 10009 2.1.0.9rc2
3787 1.0.9 1 10009 2.1.0.9
3788 1.0.10beta1 1 10010 2.1.0.10beta1
3789 1.0.10rc1 1 10010 2.1.0.10rc1
3790 1.0.10 1 10010 2.1.0.10
3791 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
3792 1.0.11rc1 1 10011 2.1.0.11rc1
3793 1.0.11 1 10011 2.1.0.11
3794 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
3795 1.0.12rc1 2 10012 2.1.0.12rc1
3796 1.0.12 2 10012 2.1.0.12
3797 1.1.0a-f - 10100 2.1.1.0a-f abandoned
3798 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
3799 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
3800 1.2.0rc1 3 10200 3.1.2.0rc1
3801 1.2.0 3 10200 3.1.2.0
3802 1.2.1beta-4 3 10201 3.1.2.1beta1-4
3803 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
3804 1.2.1 3 10201 3.1.2.1
3805 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
3806 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
3807 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
3808 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
3809 1.0.13 10 10013 10.so.0.1.0.13
3810 1.2.2 12 10202 12.so.0.1.2.2
3811 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
3812 1.2.3 12 10203 12.so.0.1.2.3
3813 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
3814 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
3815 1.0.14 10 10014 10.so.0.1.0.14
3816 1.2.4 13 10204 12.so.0.1.2.4
3817 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
3818 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
3819 1.0.15 10 10015 10.so.0.1.0.15
3820 1.2.5 13 10205 12.so.0.1.2.5
3821 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
3822 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
3823 1.0.16 10 10016 10.so.0.1.0.16
3824 1.2.6 13 10206 12.so.0.1.2.6
3825 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
3826 1.0.17rc1 10 10017 10.so.0.1.0.17rc1
3827 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
3828 1.0.17 10 10017 10.so.0.1.0.17
3829 1.2.7 13 10207 12.so.0.1.2.7
3830 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
3831 1.0.18rc1-5 10 10018 10.so.0.1.0.18rc1-5
3832 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
3833 1.0.18 10 10018 10.so.0.1.0.18
3834 1.2.8 13 10208 12.so.0.1.2.8
3835 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
3836 1.2.9beta4-11 13 10209 12.so.0.9[.0]
3837 1.2.9rc1 13 10209 12.so.0.9[.0]
3838 1.2.9 13 10209 12.so.0.9[.0]
3839 1.2.10beta1-8 13 10210 12.so.0.10[.0]
3840 1.2.10rc1-3 13 10210 12.so.0.10[.0]
3841 1.2.10 13 10210 12.so.0.10[.0]
3842 1.2.11beta1-4 13 10211 12.so.0.11[.0]
3843 1.0.19rc1-5 10 10019 10.so.0.19[.0]
3844 1.2.11rc1-5 13 10211 12.so.0.11[.0]
3845 1.0.19 10 10019 10.so.0.19[.0]
3846 1.2.11 13 10211 12.so.0.11[.0]
3847 1.0.20 10 10020 10.so.0.20[.0]
3848 1.2.12 13 10212 12.so.0.12[.0]
3849 1.2.13beta1 13 10213 12.so.0.13[.0]
3850 1.0.21 10 10021 10.so.0.21[.0]
3851 1.2.13 13 10213 12.so.0.13[.0]
3852 1.2.14beta1-2 13 10214 12.so.0.14[.0]
3853 1.0.22rc1 10 10022 10.so.0.22[.0]
3854 1.2.14rc1 13 10214 12.so.0.14[.0]
3855 1.2.15beta1-6 13 10215 12.so.0.15[.0]
3856 1.0.23rc1-5 10 10023 10.so.0.23[.0]
3857 1.2.15rc1-5 13 10215 12.so.0.15[.0]
3858 1.0.23 10 10023 10.so.0.23[.0]
3859 1.2.15 13 10215 12.so.0.15[.0]
3860 1.2.16beta1-2 13 10216 12.so.0.16[.0]
3861 1.2.16rc1 13 10216 12.so.0.16[.0]
3862 1.0.24 10 10024 10.so.0.24[.0]
3863 1.2.16 13 10216 12.so.0.16[.0]
3864 1.2.17beta1-2 13 10217 12.so.0.17[.0]
3865 1.0.25rc1 10 10025 10.so.0.25[.0]
3866 1.2.17rc1-3 13 10217 12.so.0.17[.0]
3867 1.0.25 10 10025 10.so.0.25[.0]
3868 1.2.17 13 10217 12.so.0.17[.0]
3869 1.0.26 10 10026 10.so.0.26[.0]
3870 1.2.18 13 10218 12.so.0.18[.0]
3871 1.2.19beta1-31 13 10219 12.so.0.19[.0]
3872 1.0.27rc1-6 10 10027 10.so.0.27[.0]
3873 1.2.19rc1-6 13 10219 12.so.0.19[.0]
3874 1.0.27 10 10027 10.so.0.27[.0]
3875 1.2.19 13 10219 12.so.0.19[.0]
3876 1.2.20beta01-04 13 10220 12.so.0.20[.0]
3877 1.0.28rc1-6 10 10028 10.so.0.28[.0]
3878 1.2.20rc1-6 13 10220 12.so.0.20[.0]
3879 1.0.28 10 10028 10.so.0.28[.0]
3880 1.2.20 13 10220 12.so.0.20[.0]
3881 1.2.21beta1-2 13 10221 12.so.0.21[.0]
3882 1.2.21rc1-3 13 10221 12.so.0.21[.0]
3883 1.0.29 10 10029 10.so.0.29[.0]
3884 1.2.21 13 10221 12.so.0.21[.0]
3885 1.2.22beta1-4 13 10222 12.so.0.22[.0]
3886 1.0.30rc1 13 10030 10.so.0.30[.0]
3887 1.2.22rc1 13 10222 12.so.0.22[.0]
3888 1.0.30 10 10030 10.so.0.30[.0]
3889 1.2.22 13 10222 12.so.0.22[.0]
3890 1.2.23beta01-05 13 10223 12.so.0.23[.0]
3891 1.2.23rc01 13 10223 12.so.0.23[.0]
3892 1.2.23 13 10223 12.so.0.23[.0]
3893 1.2.24beta01-02 13 10224 12.so.0.24[.0]
3894 1.2.24rc01 13 10224 12.so.0.24[.0]
3895 1.2.24 13 10224 12.so.0.24[.0]
3896 1.2.25beta01-06 13 10225 12.so.0.25[.0]
3897 1.2.25rc01-02 13 10225 12.so.0.25[.0]
3898 1.0.31 10 10031 10.so.0.31[.0]
3899 1.2.25 13 10225 12.so.0.25[.0]
3900 1.2.26beta01-06 13 10226 12.so.0.26[.0]
3901 1.2.26rc01 13 10226 12.so.0.26[.0]
3902 1.2.26 13 10226 12.so.0.26[.0]
3903 1.0.32 10 10032 10.so.0.32[.0]
3904 1.2.27beta01-06 13 10227 12.so.0.27[.0]
3905 1.2.27rc01 13 10227 12.so.0.27[.0]
3906 1.0.33 10 10033 10.so.0.33[.0]
3907 1.2.27 13 10227 12.so.0.27[.0]
3908 1.0.34 10 10034 10.so.0.34[.0]
3909 1.2.28 13 10228 12.so.0.28[.0]
3910 1.2.29beta01-03 13 10229 12.so.0.29[.0]
3911 1.2.29rc01 13 10229 12.so.0.29[.0]
3912 1.0.35 10 10035 10.so.0.35[.0]
3913 1.2.29 13 10229 12.so.0.29[.0]
3914 1.0.37 10 10037 10.so.0.37[.0]
3915 1.2.30beta01-04 13 10230 12.so.0.30[.0]
3916 1.0.38rc01-08 10 10038 10.so.0.38[.0]
3917 1.2.30rc01-08 13 10230 12.so.0.30[.0]
3918 1.0.38 10 10038 10.so.0.38[.0]
3919 1.2.30 13 10230 12.so.0.30[.0]
3920 1.0.39rc01-03 10 10039 10.so.0.39[.0]
3921 1.2.31rc01-03 13 10231 12.so.0.31[.0]
3922 1.0.39 10 10039 10.so.0.39[.0]
3923 1.2.31 13 10231 12.so.0.31[.0]
3924 1.2.32beta01-02 13 10232 12.so.0.32[.0]
3925 1.0.40rc01 10 10040 10.so.0.40[.0]
3926 1.2.32rc01 13 10232 12.so.0.32[.0]
3927 1.0.40 10 10040 10.so.0.40[.0]
3928 1.2.32 13 10232 12.so.0.32[.0]
3929 1.2.33beta01-02 13 10233 12.so.0.33[.0]
3930 1.2.33rc01-02 13 10233 12.so.0.33[.0]
3931 1.0.41rc01 10 10041 10.so.0.41[.0]
3932 1.2.33 13 10233 12.so.0.33[.0]
3933 1.0.41 10 10041 10.so.0.41[.0]
3934 1.2.34beta01-07 13 10234 12.so.0.34[.0]
3935 1.0.42rc01 10 10042 10.so.0.42[.0]
3936 1.2.34rc01 13 10234 12.so.0.34[.0]
3937 1.0.42 10 10042 10.so.0.42[.0]
3938 1.2.34 13 10234 12.so.0.34[.0]
3940 Henceforth the source version will match the shared-library minor
3941 and patch numbers; the shared-library major version number will be
3942 used for changes in backward compatibility, as it is intended. The
3943 PNG_PNGLIB_VER macro, which is not used within libpng but is available
3944 for applications, is an unsigned integer of the form xyyzz corresponding
3945 to the source version x.y.z (leading zeros in y and z). Beta versions
3946 were given the previous public release number plus a letter, until
3947 version 1.0.6j; from then on they were given the upcoming public
3948 release number plus "betaNN" or "rcN".
3951 .IR libpngpf(3) ", " png(5)
3955 http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
3956 http://www.libpng.org/pub/png
3961 (generally) at the same location as
3965 ftp://ftp.info-zip.org/pub/infozip/zlib
3968 .IR PNG specification: RFC 2083
3970 (generally) at the same location as
3974 ftp://ftp.rfc-editor.org:/in-notes/rfc2083.txt
3976 or (as a W3C Recommendation) at
3978 http://www.w3.org/TR/REC-png.html
3981 In the case of any inconsistency between the PNG specification
3982 and this library, the specification takes precedence.
3985 This man page: Glenn Randers-Pehrson
3986 <glennrp at users.sourceforge.net>
3988 The contributing authors would like to thank all those who helped
3989 with testing, bug fixes, and patience. This wouldn't have been
3990 possible without all of you.
3992 Thanks to Frank J. T. Wojcik for helping with the documentation.
3994 Libpng version 1.2.34 - December 18, 2008:
3995 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
3996 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
3998 Supported by the PNG development group
4000 png-mng-implement at lists.sf.net
4001 (subscription required; visit
4002 png-mng-implement at lists.sourceforge.net (subscription required; visit
4003 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
4006 .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
4008 (This copy of the libpng notices is provided for your convenience. In case of
4009 any discrepancy between this copy and the notices in the file png.h that is
4010 included in the libpng distribution, the latter shall prevail.)
4012 If you modify libpng you may insert additional notices immediately following
4015 libpng versions 1.2.6, August 15, 2004, through 1.2.34, December 18, 2008, are
4016 Copyright (c) 2004,2006-2008 Glenn Randers-Pehrson, and are
4017 distributed according to the same disclaimer and license as libpng-1.2.5
4018 with the following individual added to the list of Contributing Authors
4022 libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
4023 Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
4024 distributed according to the same disclaimer and license as libpng-1.0.6
4025 with the following individuals added to the list of Contributing Authors
4027 Simon-Pierre Cadieux
4031 and with the following additions to the disclaimer:
4033 There is no warranty against interference with your
4034 enjoyment of the library or against infringement.
4035 There is no warranty that our efforts or the library
4036 will fulfill any of your particular purposes or needs.
4037 This library is provided with all faults, and the entire
4038 risk of satisfactory quality, performance, accuracy, and
4039 effort is with the user.
4041 libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
4042 Copyright (c) 1998, 1999 Glenn Randers-Pehrson
4043 Distributed according to the same disclaimer and license as libpng-0.96,
4044 with the following individuals added to the list of Contributing Authors:
4047 Glenn Randers-Pehrson
4050 libpng versions 0.89, June 1996, through 0.96, May 1997, are
4051 Copyright (c) 1996, 1997 Andreas Dilger
4052 Distributed according to the same disclaimer and license as libpng-0.88,
4053 with the following individuals added to the list of Contributing Authors:
4062 libpng versions 0.5, May 1995, through 0.88, January 1996, are
4063 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
4065 For the purposes of this copyright and license, "Contributing Authors"
4066 is defined as the following set of individuals:
4074 The PNG Reference Library is supplied "AS IS". The Contributing Authors
4075 and Group 42, Inc. disclaim all warranties, expressed or implied,
4076 including, without limitation, the warranties of merchantability and of
4077 fitness for any purpose. The Contributing Authors and Group 42, Inc.
4078 assume no liability for direct, indirect, incidental, special, exemplary,
4079 or consequential damages, which may result from the use of the PNG
4080 Reference Library, even if advised of the possibility of such damage.
4082 Permission is hereby granted to use, copy, modify, and distribute this
4083 source code, or portions hereof, for any purpose, without fee, subject
4084 to the following restrictions:
4086 1. The origin of this source code must not be misrepresented.
4088 2. Altered versions must be plainly marked as such and
4089 must not be misrepresented as being the original source.
4091 3. This Copyright notice may not be removed or altered from
4092 any source or altered source distribution.
4094 The Contributing Authors and Group 42, Inc. specifically permit, without
4095 fee, and encourage the use of this source code as a component to
4096 supporting the PNG file format in commercial products. If you use this
4097 source code in a product, acknowledgment is not required but would be
4101 A "png_get_copyright" function is available, for convenient use in "about"
4104 printf("%s",png_get_copyright(NULL));
4106 Also, the PNG logo (in PNG format, of course) is supplied in the
4107 files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
4109 Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
4110 certification mark of the Open Source Initiative.
4112 Glenn Randers-Pehrson
4113 glennrp at users.sourceforge.net
projects / wxWidgets.git / blob