projects / wxWidgets.git / blame
| Commit | Line | Data |
|---|---|---|
| 0272a10d VZ |
1 | .TH LIBPNG 3 "September 8, 2007" |
| 2 | .SH NAME | |
| 3 | libpng \- Portable Network Graphics (PNG) Reference Library 1.2.20 | |
| 4 | .SH SYNOPSIS | |
| 5 | \fB | |
| 6 | #include <png.h>\fP | |
| 7 | ||
| 8 | \fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP | |
| 9 | ||
| 10 | \fBint png_check_sig (png_bytep \fP\fIsig\fP\fB, int \fInum\fP\fB);\fP | |
| 11 | ||
| 12 | \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP | |
| 13 | ||
| 14 | \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP | |
| 15 | ||
| 16 | \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP | |
| 17 | ||
| 18 | \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP | |
| 19 | ||
| 20 | \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP | |
| 21 | ||
| 22 | \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP | |
| 23 | ||
| 24 | \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 | |
| 25 | ||
| 26 | \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 | |
| 27 | ||
| 28 | \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 | |
| 29 | ||
| 30 | \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 | |
| 31 | ||
| 32 | \fBint png_debug(int \fP\fIlevel\fP\fB, png_const_charp \fImessage\fP\fB);\fP | |
| 33 | ||
| 34 | \fBint png_debug1(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fIp1\fP\fB);\fP | |
| 35 | ||
| 36 | \fBint png_debug2(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fP\fIp1\fP\fB, \fIp2\fP\fB);\fP | |
| 37 | ||
| 38 | \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP | |
| 39 | ||
| 40 | \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 | |
| 41 | ||
| 42 | \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP | |
| 43 | ||
| 44 | \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP | |
| 45 | ||
| 46 | \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP | |
| 47 | ||
| 48 | \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP | |
| 49 | ||
| 50 | \fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP | |
| 51 | ||
| 52 | \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP | |
| 53 | ||
| 54 | \fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 55 | ||
| 56 | \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 | |
| 57 | ||
| 58 | \fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 59 | ||
| 60 | \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 | |
| 61 | ||
| 62 | \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 | |
| 63 | ||
| 64 | \fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 65 | ||
| 66 | \fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 67 | ||
| 68 | \fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP | |
| 69 | ||
| 70 | \fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP | |
| 71 | ||
| 72 | \fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 73 | ||
| 74 | \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 | |
| 75 | ||
| 76 | \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 | |
| 77 | ||
| 78 | \fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP | |
| 79 | ||
| 80 | \fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP | |
| 81 | ||
| 82 | \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 | |
| 83 | ||
| 84 | \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 | |
| 85 | ||
| 86 | \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 | |
| 87 | ||
| 88 | \fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 89 | ||
| 90 | \fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 91 | ||
| 92 | \fB#if !defined(PNG_1_0_X) png_int_32 png_get_int_32 (png_bytep buf); \fI#endif | |
| 93 | ||
| 94 | \fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 95 | ||
| 96 | \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP | |
| 97 | ||
| 98 | \fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP | |
| 99 | ||
| 100 | \fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP | |
| 101 | ||
| 102 | \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 | |
| 103 | ||
| 104 | \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 | |
| 105 | ||
| 106 | \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 | |
| 107 | ||
| 108 | \fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 109 | ||
| 110 | \fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 111 | ||
| 112 | \fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP | |
| 113 | ||
| 114 | \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 | |
| 115 | ||
| 116 | \fBpng_byte png_get_rgb_to_gray_status (png_structp png_ptr) png_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 117 | ||
| 118 | \fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 119 | ||
| 120 | \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 | |
| 121 | ||
| 122 | \fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 123 | ||
| 124 | \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 | |
| 125 | ||
| 126 | \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 | |
| 127 | ||
| 128 | \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 | |
| 129 | ||
| 130 | \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 | |
| 131 | ||
| 132 | \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 | |
| 133 | ||
| 134 | \fB#if !defined(PNG_1_0_X) png_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP | |
| 135 | ||
| 136 | \fBpng_uint_32 png_get_uint_31 (png_bytep \fIbuf\fP\fB);\fP | |
| 137 | ||
| 138 | \fBpng_uint_32 png_get_uint_32 (png_bytep buf); \fI#endif | |
| 139 | ||
| 140 | \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 | |
| 141 | ||
| 142 | \fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP | |
| 143 | ||
| 144 | \fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP | |
| 145 | ||
| 146 | \fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP | |
| 147 | ||
| 148 | \fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP | |
| 149 | ||
| 150 | \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 | |
| 151 | ||
| 152 | \fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 153 | ||
| 154 | \fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 155 | ||
| 156 | \fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 157 | ||
| 158 | \fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 159 | ||
| 160 | \fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 161 | ||
| 162 | \fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 163 | ||
| 164 | \fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP | |
| 165 | ||
| 166 | \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP | |
| 167 | ||
| 168 | \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP | |
| 169 | ||
| 170 | \fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP | |
| 171 | ||
| 172 | \fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP | |
| 173 | ||
| 174 | \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP | |
| 175 | ||
| 176 | \fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP | |
| 177 | ||
| 178 | \fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP | |
| 179 | ||
| 180 | \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 | |
| 181 | ||
| 182 | \fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP | |
| 183 | ||
| 184 | \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 | |
| 185 | ||
| 186 | \fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP | |
| 187 | ||
| 188 | \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 | |
| 189 | ||
| 190 | \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 | |
| 191 | ||
| 192 | \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 | |
| 193 | ||
| 194 | \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 195 | ||
| 196 | \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP | |
| 197 | ||
| 198 | \fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP | |
| 199 | ||
| 200 | \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 | |
| 201 | ||
| 202 | \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 203 | ||
| 204 | \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 | |
| 205 | ||
| 206 | \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP | |
| 207 | ||
| 208 | \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 | |
| 209 | ||
| 210 | \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 211 | ||
| 212 | \fB#if !defined(PNG_1_0_X) png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP | |
| 213 | ||
| 214 | \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP | |
| 215 | ||
| 216 | \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP | |
| 217 | ||
| 218 | \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int flags); \fI#endif | |
| 219 | ||
| 220 | \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 | |
| 221 | ||
| 222 | \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP | |
| 223 | ||
| 224 | \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 | |
| 225 | ||
| 226 | \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 | |
| 227 | ||
| 228 | \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 | |
| 229 | ||
| 230 | \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP | |
| 231 | ||
| 232 | \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP | |
| 233 | ||
| 234 | \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP | |
| 235 | ||
| 236 | \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP | |
| 237 | ||
| 238 | \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP | |
| 239 | ||
| 240 | \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP | |
| 241 | ||
| 242 | \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 | |
| 243 | ||
| 244 | \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 | |
| 245 | ||
| 246 | \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP | |
| 247 | ||
| 248 | \fBvoid png_set_expand_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP | |
| 249 | ||
| 250 | \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP | |
| 251 | ||
| 252 | \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP | |
| 253 | ||
| 254 | \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 | |
| 255 | ||
| 256 | \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP | |
| 257 | ||
| 258 | \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP | |
| 259 | ||
| 260 | \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP | |
| 261 | ||
| 262 | \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 | |
| 263 | ||
| 264 | \fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP | |
| 265 | ||
| 266 | \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP | |
| 267 | ||
| 268 | \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 | |
| 269 | ||
| 270 | \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 | |
| 271 | ||
| 272 | \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP | |
| 273 | ||
| 274 | \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP | |
| 275 | ||
| 276 | \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP | |
| 277 | ||
| 278 | \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP | |
| 279 | ||
| 280 | \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 | |
| 281 | ||
| 282 | \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 | |
| 283 | ||
| 284 | \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 | |
| 285 | ||
| 286 | \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 | |
| 287 | ||
| 288 | \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP | |
| 289 | ||
| 290 | \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP | |
| 291 | ||
| 292 | \fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP | |
| 293 | ||
| 294 | \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 | |
| 295 | ||
| 296 | \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 | |
| 297 | ||
| 298 | \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 | |
| 299 | ||
| 300 | \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 | |
| 301 | ||
| 302 | \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 | |
| 303 | ||
| 304 | \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP | |
| 305 | ||
| 306 | \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 | |
| 307 | ||
| 308 | \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 | |
| 309 | ||
| 310 | \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 | |
| 311 | ||
| 312 | \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 | |
| 313 | ||
| 314 | \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 | |
| 315 | ||
| 316 | \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 | |
| 317 | ||
| 318 | \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP | |
| 319 | ||
| 320 | \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP | |
| 321 | ||
| 322 | \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 | |
| 323 | ||
| 324 | \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP | |
| 325 | ||
| 326 | \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 | |
| 327 | ||
| 328 | \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP | |
| 329 | ||
| 330 | \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP | |
| 331 | ||
| 332 | \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP | |
| 333 | ||
| 334 | \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP | |
| 335 | ||
| 336 | \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 | |
| 337 | ||
| 338 | \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 | |
| 339 | ||
| 340 | \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 | |
| 341 | ||
| 342 | \fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP | |
| 343 | ||
| 344 | \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 | |
| 345 | ||
| 346 | \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 | |
| 347 | ||
| 348 | \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 | |
| 349 | ||
| 350 | \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 | |
| 351 | ||
| 352 | \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 | |
| 353 | ||
| 354 | \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 | |
| 355 | ||
| 356 | \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP | |
| 357 | ||
| 358 | \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 | |
| 359 | ||
| 360 | \fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP | |
| 361 | ||
| 362 | \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 | |
| 363 | ||
| 364 | \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP | |
| 365 | ||
| 366 | \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP | |
| 367 | ||
| 368 | \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 | |
| 369 | ||
| 370 | \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 | |
| 371 | ||
| 372 | \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP | |
| 373 | ||
| 374 | \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 | |
| 375 | ||
| 376 | \fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP | |
| 377 | ||
| 378 | \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 379 | ||
| 380 | \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP | |
| 381 | ||
| 382 | \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP | |
| 383 | ||
| 384 | \fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP | |
| 385 | ||
| 386 | \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 | |
| 387 | ||
| 388 | \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 389 | ||
| 390 | \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP | |
| 391 | ||
| 392 | \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 | |
| 393 | ||
| 394 | \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP | |
| 395 | ||
| 396 | \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 | |
| 397 | ||
| 398 | \fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP | |
| 399 | ||
| 400 | \fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP | |
| 401 | ||
| 402 | .SH DESCRIPTION | |
| 403 | The | |
| 404 | .I libpng | |
| 405 | library supports encoding, decoding, and various manipulations of | |
| 406 | the Portable Network Graphics (PNG) format image files. It uses the | |
| 407 | .IR zlib(3) | |
| 408 | compression library. | |
| 409 | Following is a copy of the libpng.txt file that accompanies libpng. | |
| 410 | .SH LIBPNG.TXT | |
| 411 | libpng.txt - A description on how to use and modify libpng | |
| 412 | ||
| 413 | libpng version 1.2.20 - September 8, 2007 | |
| 414 | Updated and distributed by Glenn Randers-Pehrson | |
| 415 | <glennrp at users.sourceforge.net> | |
| 416 | Copyright (c) 1998-2007 Glenn Randers-Pehrson | |
| 417 | For conditions of distribution and use, see copyright | |
| 418 | notice in png.h. | |
| 419 | ||
| 420 | based on: | |
| 421 | ||
| 422 | libpng 1.0 beta 6 version 0.96 May 28, 1997 | |
| 423 | Updated and distributed by Andreas Dilger | |
| 424 | Copyright (c) 1996, 1997 Andreas Dilger | |
| 425 | ||
| 426 | libpng 1.0 beta 2 - version 0.88 January 26, 1996 | |
| 427 | For conditions of distribution and use, see copyright | |
| 428 | notice in png.h. Copyright (c) 1995, 1996 Guy Eric | |
| 429 | Schalnat, Group 42, Inc. | |
| 430 | ||
| 431 | Updated/rewritten per request in the libpng FAQ | |
| 432 | Copyright (c) 1995, 1996 Frank J. T. Wojcik | |
| 433 | December 18, 1995 & January 20, 1996 | |
| 434 | ||
| 435 | .SH I. Introduction | |
| 436 | ||
| 437 | This file describes how to use and modify the PNG reference library | |
| 438 | (known as libpng) for your own use. There are five sections to this | |
| 439 | file: introduction, structures, reading, writing, and modification and | |
| 440 | configuration notes for various special platforms. In addition to this | |
| 441 | file, example.c is a good starting point for using the library, as | |
| 442 | it is heavily commented and should include everything most people | |
| 443 | will need. We assume that libpng is already installed; see the | |
| 444 | INSTALL file for instructions on how to install libpng. | |
| 445 | ||
| 446 | For examples of libpng usage, see the files "example.c", "pngtest.c", | |
| 447 | and the files in the "contrib" directory, all of which are included in the | |
| 448 | libpng distribution. | |
| 449 | ||
| 450 | Libpng was written as a companion to the PNG specification, as a way | |
| 451 | of reducing the amount of time and effort it takes to support the PNG | |
| 452 | file format in application programs. | |
| 453 | ||
| 454 | The PNG specification (second edition), November 2003, is available as | |
| 455 | a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at | |
| 456 | <http://www.w3.org/TR/2003/REC-PNG-20031110/ | |
| 457 | The W3C and ISO documents have identical technical content. | |
| 458 | ||
| 459 | The PNG-1.2 specification is available at | |
| 460 | <http://www.libpng.org/pub/png/documents/> | |
| 461 | ||
| 462 | The PNG-1.0 specification is available | |
| 463 | as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a | |
| 464 | W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some | |
| 465 | additional chunks are described in the special-purpose public chunks | |
| 466 | documents at <http://www.libpng.org/pub/png/documents/>. | |
| 467 | ||
| 468 | Other information | |
| 469 | about PNG, and the latest version of libpng, can be found at the PNG home | |
| 470 | page, <http://www.libpng.org/pub/png/>. | |
| 471 | ||
| 472 | Most users will not have to modify the library significantly; advanced | |
| 473 | users may want to modify it more. All attempts were made to make it as | |
| 474 | complete as possible, while keeping the code easy to understand. | |
| 475 | Currently, this library only supports C. Support for other languages | |
| 476 | is being considered. | |
| 477 | ||
| 478 | Libpng has been designed to handle multiple sessions at one time, | |
| 479 | to be easily modifiable, to be portable to the vast majority of | |
| 480 | machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy | |
| 481 | to use. The ultimate goal of libpng is to promote the acceptance of | |
| 482 | the PNG file format in whatever way possible. While there is still | |
| 483 | work to be done (see the TODO file), libpng should cover the | |
| 484 | majority of the needs of its users. | |
| 485 | ||
| 486 | Libpng uses zlib for its compression and decompression of PNG files. | |
| 487 | Further information about zlib, and the latest version of zlib, can | |
| 488 | be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>. | |
| 489 | The zlib compression utility is a general purpose utility that is | |
| 490 | useful for more than PNG files, and can be used without libpng. | |
| 491 | See the documentation delivered with zlib for more details. | |
| 492 | You can usually find the source files for the zlib utility wherever you | |
| 493 | find the libpng source files. | |
| 494 | ||
| 495 | Libpng is thread safe, provided the threads are using different | |
| 496 | instances of the structures. Each thread should have its own | |
| 497 | png_struct and png_info instances, and thus its own image. | |
| 498 | Libpng does not protect itself against two threads using the | |
| 499 | same instance of a structure. | |
| 500 | ||
| 501 | .SH II. Structures | |
| 502 | ||
| 503 | There are two main structures that are important to libpng, png_struct | |
| 504 | and png_info. The first, png_struct, is an internal structure that | |
| 505 | will not, for the most part, be used by a user except as the first | |
| 506 | variable passed to every libpng function call. | |
| 507 | ||
| 508 | The png_info structure is designed to provide information about the | |
| 509 | PNG file. At one time, the fields of png_info were intended to be | |
| 510 | directly accessible to the user. However, this tended to cause problems | |
| 511 | with applications using dynamically loaded libraries, and as a result | |
| 512 | a set of interface functions for png_info (the png_get_*() and png_set_*() | |
| 513 | functions) was developed. The fields of png_info are still available for | |
| 514 | older applications, but it is suggested that applications use the new | |
| 515 | interfaces if at all possible. | |
| 516 | ||
| 517 | Applications that do make direct access to the members of png_struct (except | |
| 518 | for png_ptr->jmpbuf) must be recompiled whenever the library is updated, | |
| 519 | and applications that make direct access to the members of png_info must | |
| 520 | be recompiled if they were compiled or loaded with libpng version 1.0.6, | |
| 521 | in which the members were in a different order. In version 1.0.7, the | |
| 522 | members of the png_info structure reverted to the old order, as they were | |
| 523 | in versions 0.97c through 1.0.5. Starting with version 2.0.0, both | |
| 524 | structures are going to be hidden, and the contents of the structures will | |
| 525 | only be accessible through the png_get/png_set functions. | |
| 526 | ||
| 527 | The png.h header file is an invaluable reference for programming with libpng. | |
| 528 | And while I'm on the topic, make sure you include the libpng header file: | |
| 529 | ||
| 530 | #include <png.h> | |
| 531 | ||
| 532 | .SH III. Reading | |
| 533 | ||
| 534 | We'll now walk you through the possible functions to call when reading | |
| 535 | in a PNG file sequentially, briefly explaining the syntax and purpose | |
| 536 | of each one. See example.c and png.h for more detail. While | |
| 537 | progressive reading is covered in the next section, you will still | |
| 538 | need some of the functions discussed in this section to read a PNG | |
| 539 | file. | |
| 540 | ||
| 541 | .SS Setup | |
| 542 | ||
| 543 | You will want to do the I/O initialization(*) before you get into libpng, | |
| 544 | so if it doesn't work, you don't have much to undo. Of course, you | |
| 545 | will also want to insure that you are, in fact, dealing with a PNG | |
| 546 | file. Libpng provides a simple check to see if a file is a PNG file. | |
| 547 | To use it, pass in the first 1 to 8 bytes of the file to the function | |
| 548 | png_sig_cmp(), and it will return 0 if the bytes match the corresponding | |
| 549 | bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes | |
| 550 | you pass in, the greater the accuracy of the prediction. | |
| 551 | ||
| 552 | If you are intending to keep the file pointer open for use in libpng, | |
| 553 | you must ensure you don't read more than 8 bytes from the beginning | |
| 554 | of the file, and you also have to make a call to png_set_sig_bytes_read() | |
| 555 | with the number of bytes you read from the beginning. Libpng will | |
| 556 | then only check the bytes (if any) that your program didn't read. | |
| 557 | ||
| 558 | (*): If you are not using the standard I/O functions, you will need | |
| 559 | to replace them with custom functions. See the discussion under | |
| 560 | Customizing libpng. | |
| 561 | ||
| 562 | ||
| 563 | FILE *fp = fopen(file_name, "rb"); | |
| 564 | if (!fp) | |
| 565 | { | |
| 566 | return (ERROR); | |
| 567 | } | |
| 568 | fread(header, 1, number, fp); | |
| 569 | is_png = !png_sig_cmp(header, 0, number); | |
| 570 | if (!is_png) | |
| 571 | { | |
| 572 | return (NOT_PNG); | |
| 573 | } | |
| 574 | ||
| 575 | ||
| 576 | Next, png_struct and png_info need to be allocated and initialized. In | |
| 577 | order to ensure that the size of these structures is correct even with a | |
| 578 | dynamically linked libpng, there are functions to initialize and | |
| 579 | allocate the structures. We also pass the library version, optional | |
| 580 | pointers to error handling functions, and a pointer to a data struct for | |
| 581 | use by the error functions, if necessary (the pointer and functions can | |
| 582 | be NULL if the default error handlers are to be used). See the section | |
| 583 | on Changes to Libpng below regarding the old initialization functions. | |
| 584 | The structure allocation functions quietly return NULL if they fail to | |
| 585 | create the structure, so your application should check for that. | |
| 586 | ||
| 587 | png_structp png_ptr = png_create_read_struct | |
| 588 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, | |
| 589 | user_error_fn, user_warning_fn); | |
| 590 | if (!png_ptr) | |
| 591 | return (ERROR); | |
| 592 | ||
| 593 | png_infop info_ptr = png_create_info_struct(png_ptr); | |
| 594 | if (!info_ptr) | |
| 595 | { | |
| 596 | png_destroy_read_struct(&png_ptr, | |
| 597 | (png_infopp)NULL, (png_infopp)NULL); | |
| 598 | return (ERROR); | |
| 599 | } | |
| 600 | ||
| 601 | png_infop end_info = png_create_info_struct(png_ptr); | |
| 602 | if (!end_info) | |
| 603 | { | |
| 604 | png_destroy_read_struct(&png_ptr, &info_ptr, | |
| 605 | (png_infopp)NULL); | |
| 606 | return (ERROR); | |
| 607 | } | |
| 608 | ||
| 609 | If you want to use your own memory allocation routines, | |
| 610 | define PNG_USER_MEM_SUPPORTED and use | |
| 611 | png_create_read_struct_2() instead of png_create_read_struct(): | |
| 612 | ||
| 613 | png_structp png_ptr = png_create_read_struct_2 | |
| 614 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, | |
| 615 | user_error_fn, user_warning_fn, (png_voidp) | |
| 616 | user_mem_ptr, user_malloc_fn, user_free_fn); | |
| 617 | ||
| 618 | The error handling routines passed to png_create_read_struct() | |
| 619 | and the memory alloc/free routines passed to png_create_struct_2() | |
| 620 | are only necessary if you are not using the libpng supplied error | |
| 621 | handling and memory alloc/free functions. | |
| 622 | ||
| 623 | When libpng encounters an error, it expects to longjmp back | |
| 624 | to your routine. Therefore, you will need to call setjmp and pass | |
| 625 | your png_jmpbuf(png_ptr). If you read the file from different | |
| 626 | routines, you will need to update the jmpbuf field every time you enter | |
| 627 | a new routine that will call a png_*() function. | |
| 628 | ||
| 629 | See your documentation of setjmp/longjmp for your compiler for more | |
| 630 | information on setjmp/longjmp. See the discussion on libpng error | |
| 631 | handling in the Customizing Libpng section below for more information | |
| 632 | on the libpng error handling. If an error occurs, and libpng longjmp's | |
| 633 | back to your setjmp, you will want to call png_destroy_read_struct() to | |
| 634 | free any memory. | |
| 635 | ||
| 636 | if (setjmp(png_jmpbuf(png_ptr))) | |
| 637 | { | |
| 638 | png_destroy_read_struct(&png_ptr, &info_ptr, | |
| 639 | &end_info); | |
| 640 | fclose(fp); | |
| 641 | return (ERROR); | |
| 642 | } | |
| 643 | ||
| 644 | If you would rather avoid the complexity of setjmp/longjmp issues, | |
| 645 | you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case | |
| 646 | errors will result in a call to PNG_ABORT() which defaults to abort(). | |
| 647 | ||
| 648 | Now you need to set up the input code. The default for libpng is to | |
| 649 | use the C function fread(). If you use this, you will need to pass a | |
| 650 | valid FILE * in the function png_init_io(). Be sure that the file is | |
| 651 | opened in binary mode. If you wish to handle reading data in another | |
| 652 | way, you need not call the png_init_io() function, but you must then | |
| 653 | implement the libpng I/O methods discussed in the Customizing Libpng | |
| 654 | section below. | |
| 655 | ||
| 656 | png_init_io(png_ptr, fp); | |
| 657 | ||
| 658 | If you had previously opened the file and read any of the signature from | |
| 659 | the beginning in order to see if this was a PNG file, you need to let | |
| 660 | libpng know that there are some bytes missing from the start of the file. | |
| 661 | ||
| 662 | png_set_sig_bytes(png_ptr, number); | |
| 663 | ||
| 664 | .SS Setting up callback code | |
| 665 | ||
| 666 | You can set up a callback function to handle any unknown chunks in the | |
| 667 | input stream. You must supply the function | |
| 668 | ||
| 669 | read_chunk_callback(png_ptr ptr, | |
| 670 | png_unknown_chunkp chunk); | |
| 671 | { | |
| 672 | /* The unknown chunk structure contains your | |
| 673 | chunk data: */ | |
| 674 | png_byte name[5]; | |
| 675 | png_byte *data; | |
| 676 | png_size_t size; | |
| 677 | /* Note that libpng has already taken care of | |
| 678 | the CRC handling */ | |
| 679 | ||
| 680 | /* put your code here. Return one of the | |
| 681 | following: */ | |
| 682 | ||
| 683 | return (-n); /* chunk had an error */ | |
| 684 | return (0); /* did not recognize */ | |
| 685 | return (n); /* success */ | |
| 686 | } | |
| 687 | ||
| 688 | (You can give your function another name that you like instead of | |
| 689 | "read_chunk_callback") | |
| 690 | ||
| 691 | To inform libpng about your function, use | |
| 692 | ||
| 693 | png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr, | |
| 694 | read_chunk_callback); | |
| 695 | ||
| 696 | This names not only the callback function, but also a user pointer that | |
| 697 | you can retrieve with | |
| 698 | ||
| 699 | png_get_user_chunk_ptr(png_ptr); | |
| 700 | ||
| 701 | At this point, you can set up a callback function that will be | |
| 702 | called after each row has been read, which you can use to control | |
| 703 | a progress meter or the like. It's demonstrated in pngtest.c. | |
| 704 | You must supply a function | |
| 705 | ||
| 706 | void read_row_callback(png_ptr ptr, png_uint_32 row, | |
| 707 | int pass); | |
| 708 | { | |
| 709 | /* put your code here */ | |
| 710 | } | |
| 711 | ||
| 712 | (You can give it another name that you like instead of "read_row_callback") | |
| 713 | ||
| 714 | To inform libpng about your function, use | |
| 715 | ||
| 716 | png_set_read_status_fn(png_ptr, read_row_callback); | |
| 717 | ||
| 718 | .SS Width and height limits | |
| 719 | ||
| 720 | The PNG specification allows the width and height of an image to be as | |
| 721 | large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns. | |
| 722 | Since very few applications really need to process such large images, | |
| 723 | we have imposed an arbitrary 1-million limit on rows and columns. | |
| 724 | Larger images will be rejected immediately with a png_error() call. If | |
| 725 | you wish to override this limit, you can use | |
| 726 | ||
| 727 | png_set_user_limits(png_ptr, width_max, height_max); | |
| 728 | ||
| 729 | to set your own limits, or use width_max = height_max = 0x7fffffffL | |
| 730 | to allow all valid dimensions (libpng may reject some very large images | |
| 731 | anyway because of potential buffer overflow conditions). | |
| 732 | ||
| 733 | You should put this statement after you create the PNG structure and | |
| 734 | before calling png_read_info(), png_read_png(), or png_process_data(). | |
| 735 | If you need to retrieve the limits that are being applied, use | |
| 736 | ||
| 737 | width_max = png_get_user_width_max(png_ptr); | |
| 738 | height_max = png_get_user_height_max(png_ptr); | |
| 739 | ||
| 740 | .SS Unknown-chunk handling | |
| 741 | ||
| 742 | Now you get to set the way the library processes unknown chunks in the | |
| 743 | input PNG stream. Both known and unknown chunks will be read. Normal | |
| 744 | behavior is that known chunks will be parsed into information in | |
| 745 | various info_ptr members; unknown chunks will be discarded. To change | |
| 746 | this, you can call: | |
| 747 | ||
| 748 | png_set_keep_unknown_chunks(png_ptr, keep, | |
| 749 | chunk_list, num_chunks); | |
| 750 | keep - 0: do not handle as unknown | |
| 751 | 1: do not keep | |
| 752 | 2: keep only if safe-to-copy | |
| 753 | 3: keep even if unsafe-to-copy | |
| 754 | You can use these definitions: | |
| 755 | PNG_HANDLE_CHUNK_AS_DEFAULT 0 | |
| 756 | PNG_HANDLE_CHUNK_NEVER 1 | |
| 757 | PNG_HANDLE_CHUNK_IF_SAFE 2 | |
| 758 | PNG_HANDLE_CHUNK_ALWAYS 3 | |
| 759 | chunk_list - list of chunks affected (a byte string, | |
| 760 | five bytes per chunk, NULL or '\0' if | |
| 761 | num_chunks is 0) | |
| 762 | num_chunks - number of chunks affected; if 0, all | |
| 763 | unknown chunks are affected. If nonzero, | |
| 764 | only the chunks in the list are affected | |
| 765 | ||
| 766 | Unknown chunks declared in this way will be saved as raw data onto a | |
| 767 | list of png_unknown_chunk structures. If a chunk that is normally | |
| 768 | known to libpng is named in the list, it will be handled as unknown, | |
| 769 | according to the "keep" directive. If a chunk is named in successive | |
| 770 | instances of png_set_keep_unknown_chunks(), the final instance will | |
| 771 | take precedence. The IHDR and IEND chunks should not be named in | |
| 772 | chunk_list; if they are, libpng will process them normally anyway. | |
| 773 | ||
| 774 | .SS The high-level read interface | |
| 775 | ||
| 776 | At this point there are two ways to proceed; through the high-level | |
| 777 | read interface, or through a sequence of low-level read operations. | |
| 778 | You can use the high-level interface if (a) you are willing to read | |
| 779 | the entire image into memory, and (b) the input transformations | |
| 780 | you want to do are limited to the following set: | |
| 781 | ||
| 782 | PNG_TRANSFORM_IDENTITY No transformation | |
| 783 | PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to | |
| 784 | 8 bits | |
| 785 | PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel | |
| 786 | PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit | |
| 787 | samples to bytes | |
| 788 | PNG_TRANSFORM_PACKSWAP Change order of packed | |
| 789 | pixels to LSB first | |
| 790 | PNG_TRANSFORM_EXPAND Perform set_expand() | |
| 791 | PNG_TRANSFORM_INVERT_MONO Invert monochrome images | |
| 792 | PNG_TRANSFORM_SHIFT Normalize pixels to the | |
| 793 | sBIT depth | |
| 794 | PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA | |
| 795 | to BGRA | |
| 796 | PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA | |
| 797 | to AG | |
| 798 | PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity | |
| 799 | to transparency | |
| 800 | PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples | |
| 801 | ||
| 802 | (This excludes setting a background color, doing gamma transformation, | |
| 803 | dithering, and setting filler.) If this is the case, simply do this: | |
| 804 | ||
| 805 | png_read_png(png_ptr, info_ptr, png_transforms, NULL) | |
| 806 | ||
| 807 | where png_transforms is an integer containing the bitwise OR of | |
| 808 | some set of transformation flags. This call is equivalent to png_read_info(), | |
| 809 | followed the set of transformations indicated by the transform mask, | |
| 810 | then png_read_image(), and finally png_read_end(). | |
| 811 | ||
| 812 | (The final parameter of this call is not yet used. Someday it might point | |
| 813 | to transformation parameters required by some future input transform.) | |
| 814 | ||
| 815 | You must use png_transforms and not call any png_set_transform() functions | |
| 816 | when you use png_read_png(). | |
| 817 | ||
| 818 | After you have called png_read_png(), you can retrieve the image data | |
| 819 | with | |
| 820 | ||
| 821 | row_pointers = png_get_rows(png_ptr, info_ptr); | |
| 822 | ||
| 823 | where row_pointers is an array of pointers to the pixel data for each row: | |
| 824 | ||
| 825 | png_bytep row_pointers[height]; | |
| 826 | ||
| 827 | If you know your image size and pixel size ahead of time, you can allocate | |
| 828 | row_pointers prior to calling png_read_png() with | |
| 829 | ||
| 830 | if (height > PNG_UINT_32_MAX/png_sizeof(png_byte)) | |
| 831 | png_error (png_ptr, | |
| 832 | "Image is too tall to process in memory"); | |
| 833 | if (width > PNG_UINT_32_MAX/pixel_size) | |
| 834 | png_error (png_ptr, | |
| 835 | "Image is too wide to process in memory"); | |
| 836 | row_pointers = png_malloc(png_ptr, | |
| 837 | height*png_sizeof(png_bytep)); | |
| 838 | for (int i=0; i<height, i++) | |
| 839 | row_pointers[i]=png_malloc(png_ptr, | |
| 840 | width*pixel_size); | |
| 841 | png_set_rows(png_ptr, info_ptr, &row_pointers); | |
| 842 | ||
| 843 | Alternatively you could allocate your image in one big block and define | |
| 844 | row_pointers[i] to point into the proper places in your block. | |
| 845 | ||
| 846 | If you use png_set_rows(), the application is responsible for freeing | |
| 847 | row_pointers (and row_pointers[i], if they were separately allocated). | |
| 848 | ||
| 849 | If you don't allocate row_pointers ahead of time, png_read_png() will | |
| 850 | do it, and it'll be free'ed when you call png_destroy_*(). | |
| 851 | ||
| 852 | .SS The low-level read interface | |
| 853 | ||
| 854 | If you are going the low-level route, you are now ready to read all | |
| 855 | the file information up to the actual image data. You do this with a | |
| 856 | call to png_read_info(). | |
| 857 | ||
| 858 | png_read_info(png_ptr, info_ptr); | |
| 859 | ||
| 860 | This will process all chunks up to but not including the image data. | |
| 861 | ||
| 862 | .SS Querying the info structure | |
| 863 | ||
| 864 | Functions are used to get the information from the info_ptr once it | |
| 865 | has been read. Note that these fields may not be completely filled | |
| 866 | in until png_read_end() has read the chunk data following the image. | |
| 867 | ||
| 868 | png_get_IHDR(png_ptr, info_ptr, &width, &height, | |
| 869 | &bit_depth, &color_type, &interlace_type, | |
| 870 | &compression_type, &filter_method); | |
| 871 | ||
| 872 | width - holds the width of the image | |
| 873 | in pixels (up to 2^31). | |
| 874 | height - holds the height of the image | |
| 875 | in pixels (up to 2^31). | |
| 876 | bit_depth - holds the bit depth of one of the | |
| 877 | image channels. (valid values are | |
| 878 | 1, 2, 4, 8, 16 and depend also on | |
| 879 | the color_type. See also | |
| 880 | significant bits (sBIT) below). | |
| 881 | color_type - describes which color/alpha channels | |
| 882 | are present. | |
| 883 | PNG_COLOR_TYPE_GRAY | |
| 884 | (bit depths 1, 2, 4, 8, 16) | |
| 885 | PNG_COLOR_TYPE_GRAY_ALPHA | |
| 886 | (bit depths 8, 16) | |
| 887 | PNG_COLOR_TYPE_PALETTE | |
| 888 | (bit depths 1, 2, 4, 8) | |
| 889 | PNG_COLOR_TYPE_RGB | |
| 890 | (bit_depths 8, 16) | |
| 891 | PNG_COLOR_TYPE_RGB_ALPHA | |
| 892 | (bit_depths 8, 16) | |
| 893 | ||
| 894 | PNG_COLOR_MASK_PALETTE | |
| 895 | PNG_COLOR_MASK_COLOR | |
| 896 | PNG_COLOR_MASK_ALPHA | |
| 897 | ||
| 898 | filter_method - (must be PNG_FILTER_TYPE_BASE | |
| 899 | for PNG 1.0, and can also be | |
| 900 | PNG_INTRAPIXEL_DIFFERENCING if | |
| 901 | the PNG datastream is embedded in | |
| 902 | a MNG-1.0 datastream) | |
| 903 | compression_type - (must be PNG_COMPRESSION_TYPE_BASE | |
| 904 | for PNG 1.0) | |
| 905 | interlace_type - (PNG_INTERLACE_NONE or | |
| 906 | PNG_INTERLACE_ADAM7) | |
| 907 | Any or all of interlace_type, compression_type, of | |
| 908 | filter_method can be NULL if you are | |
| 909 | not interested in their values. | |
| 910 | ||
| 911 | channels = png_get_channels(png_ptr, info_ptr); | |
| 912 | channels - number of channels of info for the | |
| 913 | color type (valid values are 1 (GRAY, | |
| 914 | PALETTE), 2 (GRAY_ALPHA), 3 (RGB), | |
| 915 | 4 (RGB_ALPHA or RGB + filler byte)) | |
| 916 | rowbytes = png_get_rowbytes(png_ptr, info_ptr); | |
| 917 | rowbytes - number of bytes needed to hold a row | |
| 918 | ||
| 919 | signature = png_get_signature(png_ptr, info_ptr); | |
| 920 | signature - holds the signature read from the | |
| 921 | file (if any). The data is kept in | |
| 922 | the same offset it would be if the | |
| 923 | whole signature were read (i.e. if an | |
| 924 | application had already read in 4 | |
| 925 | bytes of signature before starting | |
| 926 | libpng, the remaining 4 bytes would | |
| 927 | be in signature[4] through signature[7] | |
| 928 | (see png_set_sig_bytes())). | |
| 929 | ||
| 930 | ||
| 931 | width = png_get_image_width(png_ptr, | |
| 932 | info_ptr); | |
| 933 | height = png_get_image_height(png_ptr, | |
| 934 | info_ptr); | |
| 935 | bit_depth = png_get_bit_depth(png_ptr, | |
| 936 | info_ptr); | |
| 937 | color_type = png_get_color_type(png_ptr, | |
| 938 | info_ptr); | |
| 939 | filter_method = png_get_filter_type(png_ptr, | |
| 940 | info_ptr); | |
| 941 | compression_type = png_get_compression_type(png_ptr, | |
| 942 | info_ptr); | |
| 943 | interlace_type = png_get_interlace_type(png_ptr, | |
| 944 | info_ptr); | |
| 945 | ||
| 946 | ||
| 947 | These are also important, but their validity depends on whether the chunk | |
| 948 | has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and | |
| 949 | png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the | |
| 950 | data has been read, or zero if it is missing. The parameters to the | |
| 951 | png_get_<chunk> are set directly if they are simple data types, or a pointer | |
| 952 | into the info_ptr is returned for any complex types. | |
| 953 | ||
| 954 | png_get_PLTE(png_ptr, info_ptr, &palette, | |
| 955 | &num_palette); | |
| 956 | palette - the palette for the file | |
| 957 | (array of png_color) | |
| 958 | num_palette - number of entries in the palette | |
| 959 | ||
| 960 | png_get_gAMA(png_ptr, info_ptr, &gamma); | |
| 961 | gamma - the gamma the file is written | |
| 962 | at (PNG_INFO_gAMA) | |
| 963 | ||
| 964 | png_get_sRGB(png_ptr, info_ptr, &srgb_intent); | |
| 965 | srgb_intent - the rendering intent (PNG_INFO_sRGB) | |
| 966 | The presence of the sRGB chunk | |
| 967 | means that the pixel data is in the | |
| 968 | sRGB color space. This chunk also | |
| 969 | implies specific values of gAMA and | |
| 970 | cHRM. | |
| 971 | ||
| 972 | png_get_iCCP(png_ptr, info_ptr, &name, | |
| 973 | &compression_type, &profile, &proflen); | |
| 974 | name - The profile name. | |
| 975 | compression - The compression type; always | |
| 976 | PNG_COMPRESSION_TYPE_BASE for PNG 1.0. | |
| 977 | You may give NULL to this argument to | |
| 978 | ignore it. | |
| 979 | profile - International Color Consortium color | |
| 980 | profile data. May contain NULs. | |
| 981 | proflen - length of profile data in bytes. | |
| 982 | ||
| 983 | png_get_sBIT(png_ptr, info_ptr, &sig_bit); | |
| 984 | sig_bit - the number of significant bits for | |
| 985 | (PNG_INFO_sBIT) each of the gray, | |
| 986 | red, green, and blue channels, | |
| 987 | whichever are appropriate for the | |
| 988 | given color type (png_color_16) | |
| 989 | ||
| 990 | png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans, | |
| 991 | &trans_values); | |
| 992 | trans - array of transparent entries for | |
| 993 | palette (PNG_INFO_tRNS) | |
| 994 | trans_values - graylevel or color sample values of | |
| 995 | the single transparent color for | |
| 996 | non-paletted images (PNG_INFO_tRNS) | |
| 997 | num_trans - number of transparent entries | |
| 998 | (PNG_INFO_tRNS) | |
| 999 | ||
| 1000 | png_get_hIST(png_ptr, info_ptr, &hist); | |
| 1001 | (PNG_INFO_hIST) | |
| 1002 | hist - histogram of palette (array of | |
| 1003 | png_uint_16) | |
| 1004 | ||
| 1005 | png_get_tIME(png_ptr, info_ptr, &mod_time); | |
| 1006 | mod_time - time image was last modified | |
| 1007 | (PNG_VALID_tIME) | |
| 1008 | ||
| 1009 | png_get_bKGD(png_ptr, info_ptr, &background); | |
| 1010 | background - background color (PNG_VALID_bKGD) | |
| 1011 | valid 16-bit red, green and blue | |
| 1012 | values, regardless of color_type | |
| 1013 | ||
| 1014 | num_comments = png_get_text(png_ptr, info_ptr, | |
| 1015 | &text_ptr, &num_text); | |
| 1016 | num_comments - number of comments | |
| 1017 | text_ptr - array of png_text holding image | |
| 1018 | comments | |
| 1019 | text_ptr[i].compression - type of compression used | |
| 1020 | on "text" PNG_TEXT_COMPRESSION_NONE | |
| 1021 | PNG_TEXT_COMPRESSION_zTXt | |
| 1022 | PNG_ITXT_COMPRESSION_NONE | |
| 1023 | PNG_ITXT_COMPRESSION_zTXt | |
| 1024 | text_ptr[i].key - keyword for comment. Must contain | |
| 1025 | 1-79 characters. | |
| 1026 | text_ptr[i].text - text comments for current | |
| 1027 | keyword. Can be empty. | |
| 1028 | text_ptr[i].text_length - length of text string, | |
| 1029 | after decompression, 0 for iTXt | |
| 1030 | text_ptr[i].itxt_length - length of itxt string, | |
| 1031 | after decompression, 0 for tEXt/zTXt | |
| 1032 | text_ptr[i].lang - language of comment (empty | |
| 1033 | string for unknown). | |
| 1034 | text_ptr[i].lang_key - keyword in UTF-8 | |
| 1035 | (empty string for unknown). | |
| 1036 | num_text - number of comments (same as | |
| 1037 | num_comments; you can put NULL here | |
| 1038 | to avoid the duplication) | |
| 1039 | Note while png_set_text() will accept text, language, | |
| 1040 | and translated keywords that can be NULL pointers, the | |
| 1041 | structure returned by png_get_text will always contain | |
| 1042 | regular zero-terminated C strings. They might be | |
| 1043 | empty strings but they will never be NULL pointers. | |
| 1044 | ||
| 1045 | num_spalettes = png_get_sPLT(png_ptr, info_ptr, | |
| 1046 | &palette_ptr); | |
| 1047 | palette_ptr - array of palette structures holding | |
| 1048 | contents of one or more sPLT chunks | |
| 1049 | read. | |
| 1050 | num_spalettes - number of sPLT chunks read. | |
| 1051 | ||
| 1052 | png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y, | |
| 1053 | &unit_type); | |
| 1054 | offset_x - positive offset from the left edge | |
| 1055 | of the screen | |
| 1056 | offset_y - positive offset from the top edge | |
| 1057 | of the screen | |
| 1058 | unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER | |
| 1059 | ||
| 1060 | png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y, | |
| 1061 | &unit_type); | |
| 1062 | res_x - pixels/unit physical resolution in | |
| 1063 | x direction | |
| 1064 | res_y - pixels/unit physical resolution in | |
| 1065 | x direction | |
| 1066 | unit_type - PNG_RESOLUTION_UNKNOWN, | |
| 1067 | PNG_RESOLUTION_METER | |
| 1068 | ||
| 1069 | png_get_sCAL(png_ptr, info_ptr, &unit, &width, | |
| 1070 | &height) | |
| 1071 | unit - physical scale units (an integer) | |
| 1072 | width - width of a pixel in physical scale units | |
| 1073 | height - height of a pixel in physical scale units | |
| 1074 | (width and height are doubles) | |
| 1075 | ||
| 1076 | png_get_sCAL_s(png_ptr, info_ptr, &unit, &width, | |
| 1077 | &height) | |
| 1078 | unit - physical scale units (an integer) | |
| 1079 | width - width of a pixel in physical scale units | |
| 1080 | height - height of a pixel in physical scale units | |
| 1081 | (width and height are strings like "2.54") | |
| 1082 | ||
| 1083 | num_unknown_chunks = png_get_unknown_chunks(png_ptr, | |
| 1084 | info_ptr, &unknowns) | |
| 1085 | unknowns - array of png_unknown_chunk | |
| 1086 | structures holding unknown chunks | |
| 1087 | unknowns[i].name - name of unknown chunk | |
| 1088 | unknowns[i].data - data of unknown chunk | |
| 1089 | unknowns[i].size - size of unknown chunk's data | |
| 1090 | unknowns[i].location - position of chunk in file | |
| 1091 | ||
| 1092 | The value of "i" corresponds to the order in which the | |
| 1093 | chunks were read from the PNG file or inserted with the | |
| 1094 | png_set_unknown_chunks() function. | |
| 1095 | ||
| 1096 | The data from the pHYs chunk can be retrieved in several convenient | |
| 1097 | forms: | |
| 1098 | ||
| 1099 | res_x = png_get_x_pixels_per_meter(png_ptr, | |
| 1100 | info_ptr) | |
| 1101 | res_y = png_get_y_pixels_per_meter(png_ptr, | |
| 1102 | info_ptr) | |
| 1103 | res_x_and_y = png_get_pixels_per_meter(png_ptr, | |
| 1104 | info_ptr) | |
| 1105 | res_x = png_get_x_pixels_per_inch(png_ptr, | |
| 1106 | info_ptr) | |
| 1107 | res_y = png_get_y_pixels_per_inch(png_ptr, | |
| 1108 | info_ptr) | |
| 1109 | res_x_and_y = png_get_pixels_per_inch(png_ptr, | |
| 1110 | info_ptr) | |
| 1111 | aspect_ratio = png_get_pixel_aspect_ratio(png_ptr, | |
| 1112 | info_ptr) | |
| 1113 | ||
| 1114 | (Each of these returns 0 [signifying "unknown"] if | |
| 1115 | the data is not present or if res_x is 0; | |
| 1116 | res_x_and_y is 0 if res_x != res_y) | |
| 1117 | ||
| 1118 | The data from the oFFs chunk can be retrieved in several convenient | |
| 1119 | forms: | |
| 1120 | ||
| 1121 | x_offset = png_get_x_offset_microns(png_ptr, info_ptr); | |
| 1122 | y_offset = png_get_y_offset_microns(png_ptr, info_ptr); | |
| 1123 | x_offset = png_get_x_offset_inches(png_ptr, info_ptr); | |
| 1124 | y_offset = png_get_y_offset_inches(png_ptr, info_ptr); | |
| 1125 | ||
| 1126 | (Each of these returns 0 [signifying "unknown" if both | |
| 1127 | x and y are 0] if the data is not present or if the | |
| 1128 | chunk is present but the unit is the pixel) | |
| 1129 | ||
| 1130 | For more information, see the png_info definition in png.h and the | |
| 1131 | PNG specification for chunk contents. Be careful with trusting | |
| 1132 | rowbytes, as some of the transformations could increase the space | |
| 1133 | needed to hold a row (expand, filler, gray_to_rgb, etc.). | |
| 1134 | See png_read_update_info(), below. | |
| 1135 | ||
| 1136 | A quick word about text_ptr and num_text. PNG stores comments in | |
| 1137 | keyword/text pairs, one pair per chunk, with no limit on the number | |
| 1138 | of text chunks, and a 2^31 byte limit on their size. While there are | |
| 1139 | suggested keywords, there is no requirement to restrict the use to these | |
| 1140 | strings. It is strongly suggested that keywords and text be sensible | |
| 1141 | to humans (that's the point), so don't use abbreviations. Non-printing | |
| 1142 | symbols are not allowed. See the PNG specification for more details. | |
| 1143 | There is also no requirement to have text after the keyword. | |
| 1144 | ||
| 1145 | Keywords should be limited to 79 Latin-1 characters without leading or | |
| 1146 | trailing spaces, but non-consecutive spaces are allowed within the | |
| 1147 | keyword. It is possible to have the same keyword any number of times. | |
| 1148 | The text_ptr is an array of png_text structures, each holding a | |
| 1149 | pointer to a language string, a pointer to a keyword and a pointer to | |
| 1150 | a text string. The text string, language code, and translated | |
| 1151 | keyword may be empty or NULL pointers. The keyword/text | |
| 1152 | pairs are put into the array in the order that they are received. | |
| 1153 | However, some or all of the text chunks may be after the image, so, to | |
| 1154 | make sure you have read all the text chunks, don't mess with these | |
| 1155 | until after you read the stuff after the image. This will be | |
| 1156 | mentioned again below in the discussion that goes with png_read_end(). | |
| 1157 | ||
| 1158 | .SS Input transformations | |
| 1159 | ||
| 1160 | After you've read the header information, you can set up the library | |
| 1161 | to handle any special transformations of the image data. The various | |
| 1162 | ways to transform the data will be described in the order that they | |
| 1163 | should occur. This is important, as some of these change the color | |
| 1164 | type and/or bit depth of the data, and some others only work on | |
| 1165 | certain color types and bit depths. Even though each transformation | |
| 1166 | checks to see if it has data that it can do something with, you should | |
| 1167 | make sure to only enable a transformation if it will be valid for the | |
| 1168 | data. For example, don't swap red and blue on grayscale data. | |
| 1169 | ||
| 1170 | The colors used for the background and transparency values should be | |
| 1171 | supplied in the same format/depth as the current image data. They | |
| 1172 | are stored in the same format/depth as the image data in a bKGD or tRNS | |
| 1173 | chunk, so this is what libpng expects for this data. The colors are | |
| 1174 | transformed to keep in sync with the image data when an application | |
| 1175 | calls the png_read_update_info() routine (see below). | |
| 1176 | ||
| 1177 | Data will be decoded into the supplied row buffers packed into bytes | |
| 1178 | unless the library has been told to transform it into another format. | |
| 1179 | For example, 4 bit/pixel paletted or grayscale data will be returned | |
| 1180 | 2 pixels/byte with the leftmost pixel in the high-order bits of the | |
| 1181 | byte, unless png_set_packing() is called. 8-bit RGB data will be stored | |
| 1182 | in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha() | |
| 1183 | is called to insert filler bytes, either before or after each RGB triplet. | |
| 1184 | 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant | |
| 1185 | byte of the color value first, unless png_set_strip_16() is called to | |
| 1186 | transform it to regular RGB RGB triplets, or png_set_filler() or | |
| 1187 | png_set_add alpha() is called to insert filler bytes, either before or | |
| 1188 | after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can | |
| 1189 | be modified with | |
| 1190 | png_set_filler(), png_set_add_alpha(), or png_set_strip_16(). | |
| 1191 | ||
| 1192 | The following code transforms grayscale images of less than 8 to 8 bits, | |
| 1193 | changes paletted images to RGB, and adds a full alpha channel if there is | |
| 1194 | transparency information in a tRNS chunk. This is most useful on | |
| 1195 | grayscale images with bit depths of 2 or 4 or if there is a multiple-image | |
| 1196 | viewing application that wishes to treat all images in the same way. | |
| 1197 | ||
| 1198 | if (color_type == PNG_COLOR_TYPE_PALETTE) | |
| 1199 | png_set_palette_to_rgb(png_ptr); | |
| 1200 | ||
| 1201 | if (color_type == PNG_COLOR_TYPE_GRAY && | |
| 1202 | bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr); | |
| 1203 | ||
| 1204 | if (png_get_valid(png_ptr, info_ptr, | |
| 1205 | PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr); | |
| 1206 | ||
| 1207 | These three functions are actually aliases for png_set_expand(), added | |
| 1208 | in libpng version 1.0.4, with the function names expanded to improve code | |
| 1209 | readability. In some future version they may actually do different | |
| 1210 | things. | |
| 1211 | ||
| 1212 | As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was | |
| 1213 | added. It expands the sample depth without changing tRNS to alpha. | |
| 1214 | At the same time, png_set_gray_1_2_4_to_8() was deprecated, and it | |
| 1215 | will be removed from a future version. | |
| 1216 | ||
| 1217 | PNG can have files with 16 bits per channel. If you only can handle | |
| 1218 | 8 bits per channel, this will strip the pixels down to 8 bit. | |
| 1219 | ||
| 1220 | if (bit_depth == 16) | |
| 1221 | png_set_strip_16(png_ptr); | |
| 1222 | ||
| 1223 | If, for some reason, you don't need the alpha channel on an image, | |
| 1224 | and you want to remove it rather than combining it with the background | |
| 1225 | (but the image author certainly had in mind that you *would* combine | |
| 1226 | it with the background, so that's what you should probably do): | |
| 1227 | ||
| 1228 | if (color_type & PNG_COLOR_MASK_ALPHA) | |
| 1229 | png_set_strip_alpha(png_ptr); | |
| 1230 | ||
| 1231 | In PNG files, the alpha channel in an image | |
| 1232 | is the level of opacity. If you need the alpha channel in an image to | |
| 1233 | be the level of transparency instead of opacity, you can invert the | |
| 1234 | alpha channel (or the tRNS chunk data) after it's read, so that 0 is | |
| 1235 | fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit | |
| 1236 | images) is fully transparent, with | |
| 1237 | ||
| 1238 | png_set_invert_alpha(png_ptr); | |
| 1239 | ||
| 1240 | PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as | |
| 1241 | they can, resulting in, for example, 8 pixels per byte for 1 bit | |
| 1242 | files. This code expands to 1 pixel per byte without changing the | |
| 1243 | values of the pixels: | |
| 1244 | ||
| 1245 | if (bit_depth < 8) | |
| 1246 | png_set_packing(png_ptr); | |
| 1247 | ||
| 1248 | PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels | |
| 1249 | stored in a PNG image have been "scaled" or "shifted" up to the next | |
| 1250 | higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to | |
| 1251 | 8 bits/sample in the range [0, 255]). However, it is also possible to | |
| 1252 | convert the PNG pixel data back to the original bit depth of the image. | |
| 1253 | This call reduces the pixels back down to the original bit depth: | |
| 1254 | ||
| 1255 | png_color_8p sig_bit; | |
| 1256 | ||
| 1257 | if (png_get_sBIT(png_ptr, info_ptr, &sig_bit)) | |
| 1258 | png_set_shift(png_ptr, sig_bit); | |
| 1259 | ||
| 1260 | PNG files store 3-color pixels in red, green, blue order. This code | |
| 1261 | changes the storage of the pixels to blue, green, red: | |
| 1262 | ||
| 1263 | if (color_type == PNG_COLOR_TYPE_RGB || | |
| 1264 | color_type == PNG_COLOR_TYPE_RGB_ALPHA) | |
| 1265 | png_set_bgr(png_ptr); | |
| 1266 | ||
| 1267 | PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them | |
| 1268 | into 4 or 8 bytes for windowing systems that need them in this format: | |
| 1269 | ||
| 1270 | if (color_type == PNG_COLOR_TYPE_RGB) | |
| 1271 | png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE); | |
| 1272 | ||
| 1273 | where "filler" is the 8 or 16-bit number to fill with, and the location is | |
| 1274 | either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether | |
| 1275 | you want the filler before the RGB or after. This transformation | |
| 1276 | does not affect images that already have full alpha channels. To add an | |
| 1277 | opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which | |
| 1278 | will generate RGBA pixels. | |
| 1279 | ||
| 1280 | Note that png_set_filler() does not change the color type. If you want | |
| 1281 | to do that, you can add a true alpha channel with | |
| 1282 | ||
| 1283 | if (color_type == PNG_COLOR_TYPE_RGB || | |
| 1284 | color_type == PNG_COLOR_TYPE_GRAY) | |
| 1285 | png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER); | |
| 1286 | ||
| 1287 | where "filler" contains the alpha value to assign to each pixel. | |
| 1288 | This function was added in libpng-1.2.7. | |
| 1289 | ||
| 1290 | If you are reading an image with an alpha channel, and you need the | |
| 1291 | data as ARGB instead of the normal PNG format RGBA: | |
| 1292 | ||
| 1293 | if (color_type == PNG_COLOR_TYPE_RGB_ALPHA) | |
| 1294 | png_set_swap_alpha(png_ptr); | |
| 1295 | ||
| 1296 | For some uses, you may want a grayscale image to be represented as | |
| 1297 | RGB. This code will do that conversion: | |
| 1298 | ||
| 1299 | if (color_type == PNG_COLOR_TYPE_GRAY || | |
| 1300 | color_type == PNG_COLOR_TYPE_GRAY_ALPHA) | |
| 1301 | png_set_gray_to_rgb(png_ptr); | |
| 1302 | ||
| 1303 | Conversely, you can convert an RGB or RGBA image to grayscale or grayscale | |
| 1304 | with alpha. | |
| 1305 | ||
| 1306 | if (color_type == PNG_COLOR_TYPE_RGB || | |
| 1307 | color_type == PNG_COLOR_TYPE_RGB_ALPHA) | |
| 1308 | png_set_rgb_to_gray_fixed(png_ptr, error_action, | |
| 1309 | int red_weight, int green_weight); | |
| 1310 | ||
| 1311 | error_action = 1: silently do the conversion | |
| 1312 | error_action = 2: issue a warning if the original | |
| 1313 | image has any pixel where | |
| 1314 | red != green or red != blue | |
| 1315 | error_action = 3: issue an error and abort the | |
| 1316 | conversion if the original | |
| 1317 | image has any pixel where | |
| 1318 | red != green or red != blue | |
| 1319 | ||
| 1320 | red_weight: weight of red component times 100000 | |
| 1321 | green_weight: weight of green component times 100000 | |
| 1322 | If either weight is negative, default | |
| 1323 | weights (21268, 71514) are used. | |
| 1324 | ||
| 1325 | If you have set error_action = 1 or 2, you can | |
| 1326 | later check whether the image really was gray, after processing | |
| 1327 | the image rows, with the png_get_rgb_to_gray_status(png_ptr) function. | |
| 1328 | It will return a png_byte that is zero if the image was gray or | |
| 1329 | 1 if there were any non-gray pixels. bKGD and sBIT data | |
| 1330 | will be silently converted to grayscale, using the green channel | |
| 1331 | data, regardless of the error_action setting. | |
| 1332 | ||
| 1333 | With red_weight+green_weight<=100000, | |
| 1334 | the normalized graylevel is computed: | |
| 1335 | ||
| 1336 | int rw = red_weight * 65536; | |
| 1337 | int gw = green_weight * 65536; | |
| 1338 | int bw = 65536 - (rw + gw); | |
| 1339 | gray = (rw*red + gw*green + bw*blue)/65536; | |
| 1340 | ||
| 1341 | The default values approximate those recommended in the Charles | |
| 1342 | Poynton's Color FAQ, <http://www.inforamp.net/~poynton/> | |
| 1343 | Copyright (c) 1998-01-04 Charles Poynton <poynton at inforamp.net> | |
| 1344 | ||
| 1345 | Y = 0.212671 * R + 0.715160 * G + 0.072169 * B | |
| 1346 | ||
| 1347 | Libpng approximates this with | |
| 1348 | ||
| 1349 | Y = 0.21268 * R + 0.7151 * G + 0.07217 * B | |
| 1350 | ||
| 1351 | which can be expressed with integers as | |
| 1352 | ||
| 1353 | Y = (6969 * R + 23434 * G + 2365 * B)/32768 | |
| 1354 | ||
| 1355 | The calculation is done in a linear colorspace, if the image gamma | |
| 1356 | is known. | |
| 1357 | ||
| 1358 | If you have a grayscale and you are using png_set_expand_depth(), | |
| 1359 | png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to | |
| 1360 | a higher bit-depth, you must either supply the background color as a gray | |
| 1361 | value at the original file bit-depth (need_expand = 1) or else supply the | |
| 1362 | background color as an RGB triplet at the final, expanded bit depth | |
| 1363 | (need_expand = 0). Similarly, if you are reading a paletted image, you | |
| 1364 | must either supply the background color as a palette index (need_expand = 1) | |
| 1365 | or as an RGB triplet that may or may not be in the palette (need_expand = 0). | |
| 1366 | ||
| 1367 | png_color_16 my_background; | |
| 1368 | png_color_16p image_background; | |
| 1369 | ||
| 1370 | if (png_get_bKGD(png_ptr, info_ptr, &image_background)) | |
| 1371 | png_set_background(png_ptr, image_background, | |
| 1372 | PNG_BACKGROUND_GAMMA_FILE, 1, 1.0); | |
| 1373 | else | |
| 1374 | png_set_background(png_ptr, &my_background, | |
| 1375 | PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0); | |
| 1376 | ||
| 1377 | The png_set_background() function tells libpng to composite images | |
| 1378 | with alpha or simple transparency against the supplied background | |
| 1379 | color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid), | |
| 1380 | you may use this color, or supply another color more suitable for | |
| 1381 | the current display (e.g., the background color from a web page). You | |
| 1382 | need to tell libpng whether the color is in the gamma space of the | |
| 1383 | display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file | |
| 1384 | (PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one | |
| 1385 | that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't | |
| 1386 | know why anyone would use this, but it's here). | |
| 1387 | ||
| 1388 | To properly display PNG images on any kind of system, the application needs | |
| 1389 | to know what the display gamma is. Ideally, the user will know this, and | |
| 1390 | the application will allow them to set it. One method of allowing the user | |
| 1391 | to set the display gamma separately for each system is to check for a | |
| 1392 | SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be | |
| 1393 | correctly set. | |
| 1394 | ||
| 1395 | Note that display_gamma is the overall gamma correction required to produce | |
| 1396 | pleasing results, which depends on the lighting conditions in the surrounding | |
| 1397 | environment. In a dim or brightly lit room, no compensation other than | |
| 1398 | the physical gamma exponent of the monitor is needed, while in a dark room | |
| 1399 | a slightly smaller exponent is better. | |
| 1400 | ||
| 1401 | double gamma, screen_gamma; | |
| 1402 | ||
| 1403 | if (/* We have a user-defined screen | |
| 1404 | gamma value */) | |
| 1405 | { | |
| 1406 | screen_gamma = user_defined_screen_gamma; | |
| 1407 | } | |
| 1408 | /* One way that applications can share the same | |
| 1409 | screen gamma value */ | |
| 1410 | else if ((gamma_str = getenv("SCREEN_GAMMA")) | |
| 1411 | != NULL) | |
| 1412 | { | |
| 1413 | screen_gamma = (double)atof(gamma_str); | |
| 1414 | } | |
| 1415 | /* If we don't have another value */ | |
| 1416 | else | |
| 1417 | { | |
| 1418 | screen_gamma = 2.2; /* A good guess for a | |
| 1419 | PC monitor in a bright office or a dim room */ | |
| 1420 | screen_gamma = 2.0; /* A good guess for a | |
| 1421 | PC monitor in a dark room */ | |
| 1422 | screen_gamma = 1.7 or 1.0; /* A good | |
| 1423 | guess for Mac systems */ | |
| 1424 | } | |
| 1425 | ||
| 1426 | The png_set_gamma() function handles gamma transformations of the data. | |
| 1427 | Pass both the file gamma and the current screen_gamma. If the file does | |
| 1428 | not have a gamma value, you can pass one anyway if you have an idea what | |
| 1429 | it is (usually 0.45455 is a good guess for GIF images on PCs). Note | |
| 1430 | that file gammas are inverted from screen gammas. See the discussions | |
| 1431 | on gamma in the PNG specification for an excellent description of what | |
| 1432 | gamma is, and why all applications should support it. It is strongly | |
| 1433 | recommended that PNG viewers support gamma correction. | |
| 1434 | ||
| 1435 | if (png_get_gAMA(png_ptr, info_ptr, &gamma)) | |
| 1436 | png_set_gamma(png_ptr, screen_gamma, gamma); | |
| 1437 | else | |
| 1438 | png_set_gamma(png_ptr, screen_gamma, 0.45455); | |
| 1439 | ||
| 1440 | If you need to reduce an RGB file to a paletted file, or if a paletted | |
| 1441 | file has more entries then will fit on your screen, png_set_dither() | |
| 1442 | will do that. Note that this is a simple match dither that merely | |
| 1443 | finds the closest color available. This should work fairly well with | |
| 1444 | optimized palettes, and fairly badly with linear color cubes. If you | |
| 1445 | pass a palette that is larger then maximum_colors, the file will | |
| 1446 | reduce the number of colors in the palette so it will fit into | |
| 1447 | maximum_colors. If there is a histogram, it will use it to make | |
| 1448 | more intelligent choices when reducing the palette. If there is no | |
| 1449 | histogram, it may not do as good a job. | |
| 1450 | ||
| 1451 | if (color_type & PNG_COLOR_MASK_COLOR) | |
| 1452 | { | |
| 1453 | if (png_get_valid(png_ptr, info_ptr, | |
| 1454 | PNG_INFO_PLTE)) | |
| 1455 | { | |
| 1456 | png_uint_16p histogram = NULL; | |
| 1457 | ||
| 1458 | png_get_hIST(png_ptr, info_ptr, | |
| 1459 | &histogram); | |
| 1460 | png_set_dither(png_ptr, palette, num_palette, | |
| 1461 | max_screen_colors, histogram, 1); | |
| 1462 | } | |
| 1463 | else | |
| 1464 | { | |
| 1465 | png_color std_color_cube[MAX_SCREEN_COLORS] = | |
| 1466 | { ... colors ... }; | |
| 1467 | ||
| 1468 | png_set_dither(png_ptr, std_color_cube, | |
| 1469 | MAX_SCREEN_COLORS, MAX_SCREEN_COLORS, | |
| 1470 | NULL,0); | |
| 1471 | } | |
| 1472 | } | |
| 1473 | ||
| 1474 | PNG files describe monochrome as black being zero and white being one. | |
| 1475 | The following code will reverse this (make black be one and white be | |
| 1476 | zero): | |
| 1477 | ||
| 1478 | if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY) | |
| 1479 | png_set_invert_mono(png_ptr); | |
| 1480 | ||
| 1481 | This function can also be used to invert grayscale and gray-alpha images: | |
| 1482 | ||
| 1483 | if (color_type == PNG_COLOR_TYPE_GRAY || | |
| 1484 | color_type == PNG_COLOR_TYPE_GRAY_ALPHA) | |
| 1485 | png_set_invert_mono(png_ptr); | |
| 1486 | ||
| 1487 | PNG files store 16 bit pixels in network byte order (big-endian, | |
| 1488 | ie. most significant bits first). This code changes the storage to the | |
| 1489 | other way (little-endian, i.e. least significant bits first, the | |
| 1490 | way PCs store them): | |
| 1491 | ||
| 1492 | if (bit_depth == 16) | |
| 1493 | png_set_swap(png_ptr); | |
| 1494 | ||
| 1495 | If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you | |
| 1496 | need to change the order the pixels are packed into bytes, you can use: | |
| 1497 | ||
| 1498 | if (bit_depth < 8) | |
| 1499 | png_set_packswap(png_ptr); | |
| 1500 | ||
| 1501 | Finally, you can write your own transformation function if none of | |
| 1502 | the existing ones meets your needs. This is done by setting a callback | |
| 1503 | with | |
| 1504 | ||
| 1505 | png_set_read_user_transform_fn(png_ptr, | |
| 1506 | read_transform_fn); | |
| 1507 | ||
| 1508 | You must supply the function | |
| 1509 | ||
| 1510 | void read_transform_fn(png_ptr ptr, row_info_ptr | |
| 1511 | row_info, png_bytep data) | |
| 1512 | ||
| 1513 | See pngtest.c for a working example. Your function will be called | |
| 1514 | after all of the other transformations have been processed. | |
| 1515 | ||
| 1516 | You can also set up a pointer to a user structure for use by your | |
| 1517 | callback function, and you can inform libpng that your transform | |
| 1518 | function will change the number of channels or bit depth with the | |
| 1519 | function | |
| 1520 | ||
| 1521 | png_set_user_transform_info(png_ptr, user_ptr, | |
| 1522 | user_depth, user_channels); | |
| 1523 | ||
| 1524 | The user's application, not libpng, is responsible for allocating and | |
| 1525 | freeing any memory required for the user structure. | |
| 1526 | ||
| 1527 | You can retrieve the pointer via the function | |
| 1528 | png_get_user_transform_ptr(). For example: | |
| 1529 | ||
| 1530 | voidp read_user_transform_ptr = | |
| 1531 | png_get_user_transform_ptr(png_ptr); | |
| 1532 | ||
| 1533 | The last thing to handle is interlacing; this is covered in detail below, | |
| 1534 | but you must call the function here if you want libpng to handle expansion | |
| 1535 | of the interlaced image. | |
| 1536 | ||
| 1537 | number_of_passes = png_set_interlace_handling(png_ptr); | |
| 1538 | ||
| 1539 | After setting the transformations, libpng can update your png_info | |
| 1540 | structure to reflect any transformations you've requested with this | |
| 1541 | call. This is most useful to update the info structure's rowbytes | |
| 1542 | field so you can use it to allocate your image memory. This function | |
| 1543 | will also update your palette with the correct screen_gamma and | |
| 1544 | background if these have been given with the calls above. | |
| 1545 | ||
| 1546 | png_read_update_info(png_ptr, info_ptr); | |
| 1547 | ||
| 1548 | After you call png_read_update_info(), you can allocate any | |
| 1549 | memory you need to hold the image. The row data is simply | |
| 1550 | raw byte data for all forms of images. As the actual allocation | |
| 1551 | varies among applications, no example will be given. If you | |
| 1552 | are allocating one large chunk, you will need to build an | |
| 1553 | array of pointers to each row, as it will be needed for some | |
| 1554 | of the functions below. | |
| 1555 | ||
| 1556 | .SS Reading image data | |
| 1557 | ||
| 1558 | After you've allocated memory, you can read the image data. | |
| 1559 | The simplest way to do this is in one function call. If you are | |
| 1560 | allocating enough memory to hold the whole image, you can just | |
| 1561 | call png_read_image() and libpng will read in all the image data | |
| 1562 | and put it in the memory area supplied. You will need to pass in | |
| 1563 | an array of pointers to each row. | |
| 1564 | ||
| 1565 | This function automatically handles interlacing, so you don't need | |
| 1566 | to call png_set_interlace_handling() or call this function multiple | |
| 1567 | times, or any of that other stuff necessary with png_read_rows(). | |
| 1568 | ||
| 1569 | png_read_image(png_ptr, row_pointers); | |
| 1570 | ||
| 1571 | where row_pointers is: | |
| 1572 | ||
| 1573 | png_bytep row_pointers[height]; | |
| 1574 | ||
| 1575 | You can point to void or char or whatever you use for pixels. | |
| 1576 | ||
| 1577 | If you don't want to read in the whole image at once, you can | |
| 1578 | use png_read_rows() instead. If there is no interlacing (check | |
| 1579 | interlace_type == PNG_INTERLACE_NONE), this is simple: | |
| 1580 | ||
| 1581 | png_read_rows(png_ptr, row_pointers, NULL, | |
| 1582 | number_of_rows); | |
| 1583 | ||
| 1584 | where row_pointers is the same as in the png_read_image() call. | |
| 1585 | ||
| 1586 | If you are doing this just one row at a time, you can do this with | |
| 1587 | a single row_pointer instead of an array of row_pointers: | |
| 1588 | ||
| 1589 | png_bytep row_pointer = row; | |
| 1590 | png_read_row(png_ptr, row_pointer, NULL); | |
| 1591 | ||
| 1592 | If the file is interlaced (interlace_type != 0 in the IHDR chunk), things | |
| 1593 | get somewhat harder. The only current (PNG Specification version 1.2) | |
| 1594 | interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7) | |
| 1595 | is a somewhat complicated 2D interlace scheme, known as Adam7, that | |
| 1596 | breaks down an image into seven smaller images of varying size, based | |
| 1597 | on an 8x8 grid. | |
| 1598 | ||
| 1599 | libpng can fill out those images or it can give them to you "as is". | |
| 1600 | If you want them filled out, there are two ways to do that. The one | |
| 1601 | mentioned in the PNG specification is to expand each pixel to cover | |
| 1602 | those pixels that have not been read yet (the "rectangle" method). | |
| 1603 | This results in a blocky image for the first pass, which gradually | |
| 1604 | smooths out as more pixels are read. The other method is the "sparkle" | |
| 1605 | method, where pixels are drawn only in their final locations, with the | |
| 1606 | rest of the image remaining whatever colors they were initialized to | |
| 1607 | before the start of the read. The first method usually looks better, | |
| 1608 | but tends to be slower, as there are more pixels to put in the rows. | |
| 1609 | ||
| 1610 | If you don't want libpng to handle the interlacing details, just call | |
| 1611 | png_read_rows() seven times to read in all seven images. Each of the | |
| 1612 | images is a valid image by itself, or they can all be combined on an | |
| 1613 | 8x8 grid to form a single image (although if you intend to combine them | |
| 1614 | you would be far better off using the libpng interlace handling). | |
| 1615 | ||
| 1616 | The first pass will return an image 1/8 as wide as the entire image | |
| 1617 | (every 8th column starting in column 0) and 1/8 as high as the original | |
| 1618 | (every 8th row starting in row 0), the second will be 1/8 as wide | |
| 1619 | (starting in column 4) and 1/8 as high (also starting in row 0). The | |
| 1620 | third pass will be 1/4 as wide (every 4th pixel starting in column 0) and | |
| 1621 | 1/8 as high (every 8th row starting in row 4), and the fourth pass will | |
| 1622 | be 1/4 as wide and 1/4 as high (every 4th column starting in column 2, | |
| 1623 | and every 4th row starting in row 0). The fifth pass will return an | |
| 1624 | image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2), | |
| 1625 | while the sixth pass will be 1/2 as wide and 1/2 as high as the original | |
| 1626 | (starting in column 1 and row 0). The seventh and final pass will be as | |
| 1627 | wide as the original, and 1/2 as high, containing all of the odd | |
| 1628 | numbered scanlines. Phew! | |
| 1629 | ||
| 1630 | If you want libpng to expand the images, call this before calling | |
| 1631 | png_start_read_image() or png_read_update_info(): | |
| 1632 | ||
| 1633 | if (interlace_type == PNG_INTERLACE_ADAM7) | |
| 1634 | number_of_passes | |
| 1635 | = png_set_interlace_handling(png_ptr); | |
| 1636 | ||
| 1637 | This will return the number of passes needed. Currently, this | |
| 1638 | is seven, but may change if another interlace type is added. | |
| 1639 | This function can be called even if the file is not interlaced, | |
| 1640 | where it will return one pass. | |
| 1641 | ||
| 1642 | If you are not going to display the image after each pass, but are | |
| 1643 | going to wait until the entire image is read in, use the sparkle | |
| 1644 | effect. This effect is faster and the end result of either method | |
| 1645 | is exactly the same. If you are planning on displaying the image | |
| 1646 | after each pass, the "rectangle" effect is generally considered the | |
| 1647 | better looking one. | |
| 1648 | ||
| 1649 | If you only want the "sparkle" effect, just call png_read_rows() as | |
| 1650 | normal, with the third parameter NULL. Make sure you make pass over | |
| 1651 | the image number_of_passes times, and you don't change the data in the | |
| 1652 | rows between calls. You can change the locations of the data, just | |
| 1653 | not the data. Each pass only writes the pixels appropriate for that | |
| 1654 | pass, and assumes the data from previous passes is still valid. | |
| 1655 | ||
| 1656 | png_read_rows(png_ptr, row_pointers, NULL, | |
| 1657 | number_of_rows); | |
| 1658 | ||
| 1659 | If you only want the first effect (the rectangles), do the same as | |
| 1660 | before except pass the row buffer in the third parameter, and leave | |
| 1661 | the second parameter NULL. | |
| 1662 | ||
| 1663 | png_read_rows(png_ptr, NULL, row_pointers, | |
| 1664 | number_of_rows); | |
| 1665 | ||
| 1666 | .SS Finishing a sequential read | |
| 1667 | ||
| 1668 | After you are finished reading the image through the | |
| 1669 | low-level interface, you can finish reading the file. If you are | |
| 1670 | interested in comments or time, which may be stored either before or | |
| 1671 | after the image data, you should pass the separate png_info struct if | |
| 1672 | you want to keep the comments from before and after the image | |
| 1673 | separate. If you are not interested, you can pass NULL. | |
| 1674 | ||
| 1675 | png_read_end(png_ptr, end_info); | |
| 1676 | ||
| 1677 | When you are done, you can free all memory allocated by libpng like this: | |
| 1678 | ||
| 1679 | png_destroy_read_struct(&png_ptr, &info_ptr, | |
| 1680 | &end_info); | |
| 1681 | ||
| 1682 | It is also possible to individually free the info_ptr members that | |
| 1683 | point to libpng-allocated storage with the following function: | |
| 1684 | ||
| 1685 | png_free_data(png_ptr, info_ptr, mask, seq) | |
| 1686 | mask - identifies data to be freed, a mask | |
| 1687 | containing the bitwise OR of one or | |
| 1688 | more of | |
| 1689 | PNG_FREE_PLTE, PNG_FREE_TRNS, | |
| 1690 | PNG_FREE_HIST, PNG_FREE_ICCP, | |
| 1691 | PNG_FREE_PCAL, PNG_FREE_ROWS, | |
| 1692 | PNG_FREE_SCAL, PNG_FREE_SPLT, | |
| 1693 | PNG_FREE_TEXT, PNG_FREE_UNKN, | |
| 1694 | or simply PNG_FREE_ALL | |
| 1695 | seq - sequence number of item to be freed | |
| 1696 | (-1 for all items) | |
| 1697 | ||
| 1698 | This function may be safely called when the relevant storage has | |
| 1699 | already been freed, or has not yet been allocated, or was allocated | |
| 1700 | by the user and not by libpng, and will in those | |
| 1701 | cases do nothing. The "seq" parameter is ignored if only one item | |
| 1702 | of the selected data type, such as PLTE, is allowed. If "seq" is not | |
| 1703 | -1, and multiple items are allowed for the data type identified in | |
| 1704 | the mask, such as text or sPLT, only the n'th item in the structure | |
| 1705 | is freed, where n is "seq". | |
| 1706 | ||
| 1707 | The default behavior is only to free data that was allocated internally | |
| 1708 | by libpng. This can be changed, so that libpng will not free the data, | |
| 1709 | or so that it will free data that was allocated by the user with png_malloc() | |
| 1710 | or png_zalloc() and passed in via a png_set_*() function, with | |
| 1711 | ||
| 1712 | png_data_freer(png_ptr, info_ptr, freer, mask) | |
| 1713 | mask - which data elements are affected | |
| 1714 | same choices as in png_free_data() | |
| 1715 | freer - one of | |
| 1716 | PNG_DESTROY_WILL_FREE_DATA | |
| 1717 | PNG_SET_WILL_FREE_DATA | |
| 1718 | PNG_USER_WILL_FREE_DATA | |
| 1719 | ||
| 1720 | This function only affects data that has already been allocated. | |
| 1721 | You can call this function after reading the PNG data but before calling | |
| 1722 | any png_set_*() functions, to control whether the user or the png_set_*() | |
| 1723 | function is responsible for freeing any existing data that might be present, | |
| 1724 | and again after the png_set_*() functions to control whether the user | |
| 1725 | or png_destroy_*() is supposed to free the data. When the user assumes | |
| 1726 | responsibility for libpng-allocated data, the application must use | |
| 1727 | png_free() to free it, and when the user transfers responsibility to libpng | |
| 1728 | for data that the user has allocated, the user must have used png_malloc() | |
| 1729 | or png_zalloc() to allocate it. | |
| 1730 | ||
| 1731 | If you allocated your row_pointers in a single block, as suggested above in | |
| 1732 | the description of the high level read interface, you must not transfer | |
| 1733 | responsibility for freeing it to the png_set_rows or png_read_destroy function, | |
| 1734 | because they would also try to free the individual row_pointers[i]. | |
| 1735 | ||
| 1736 | If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword | |
| 1737 | separately, do not transfer responsibility for freeing text_ptr to libpng, | |
| 1738 | because when libpng fills a png_text structure it combines these members with | |
| 1739 | the key member, and png_free_data() will free only text_ptr.key. Similarly, | |
| 1740 | if you transfer responsibility for free'ing text_ptr from libpng to your | |
| 1741 | application, your application must not separately free those members. | |
| 1742 | ||
| 1743 | The png_free_data() function will turn off the "valid" flag for anything | |
| 1744 | it frees. If you need to turn the flag off for a chunk that was freed by your | |
| 1745 | application instead of by libpng, you can use | |
| 1746 | ||
| 1747 | png_set_invalid(png_ptr, info_ptr, mask); | |
| 1748 | mask - identifies the chunks to be made invalid, | |
| 1749 | containing the bitwise OR of one or | |
| 1750 | more of | |
| 1751 | PNG_INFO_gAMA, PNG_INFO_sBIT, | |
| 1752 | PNG_INFO_cHRM, PNG_INFO_PLTE, | |
| 1753 | PNG_INFO_tRNS, PNG_INFO_bKGD, | |
| 1754 | PNG_INFO_hIST, PNG_INFO_pHYs, | |
| 1755 | PNG_INFO_oFFs, PNG_INFO_tIME, | |
| 1756 | PNG_INFO_pCAL, PNG_INFO_sRGB, | |
| 1757 | PNG_INFO_iCCP, PNG_INFO_sPLT, | |
| 1758 | PNG_INFO_sCAL, PNG_INFO_IDAT | |
| 1759 | ||
| 1760 | For a more compact example of reading a PNG image, see the file example.c. | |
| 1761 | ||
| 1762 | .SS Reading PNG files progressively | |
| 1763 | ||
| 1764 | The progressive reader is slightly different then the non-progressive | |
| 1765 | reader. Instead of calling png_read_info(), png_read_rows(), and | |
| 1766 | png_read_end(), you make one call to png_process_data(), which calls | |
| 1767 | callbacks when it has the info, a row, or the end of the image. You | |
| 1768 | set up these callbacks with png_set_progressive_read_fn(). You don't | |
| 1769 | have to worry about the input/output functions of libpng, as you are | |
| 1770 | giving the library the data directly in png_process_data(). I will | |
| 1771 | assume that you have read the section on reading PNG files above, | |
| 1772 | so I will only highlight the differences (although I will show | |
| 1773 | all of the code). | |
| 1774 | ||
| 1775 | png_structp png_ptr; | |
| 1776 | png_infop info_ptr; | |
| 1777 | ||
| 1778 | /* An example code fragment of how you would | |
| 1779 | initialize the progressive reader in your | |
| 1780 | application. */ | |
| 1781 | int | |
| 1782 | initialize_png_reader() | |
| 1783 | { | |
| 1784 | png_ptr = png_create_read_struct | |
| 1785 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, | |
| 1786 | user_error_fn, user_warning_fn); | |
| 1787 | if (!png_ptr) | |
| 1788 | return (ERROR); | |
| 1789 | info_ptr = png_create_info_struct(png_ptr); | |
| 1790 | if (!info_ptr) | |
| 1791 | { | |
| 1792 | png_destroy_read_struct(&png_ptr, (png_infopp)NULL, | |
| 1793 | (png_infopp)NULL); | |
| 1794 | return (ERROR); | |
| 1795 | } | |
| 1796 | ||
| 1797 | if (setjmp(png_jmpbuf(png_ptr))) | |
| 1798 | { | |
| 1799 | png_destroy_read_struct(&png_ptr, &info_ptr, | |
| 1800 | (png_infopp)NULL); | |
| 1801 | return (ERROR); | |
| 1802 | } | |
| 1803 | ||
| 1804 | /* This one's new. You can provide functions | |
| 1805 | to be called when the header info is valid, | |
| 1806 | when each row is completed, and when the image | |
| 1807 | is finished. If you aren't using all functions, | |
| 1808 | you can specify NULL parameters. Even when all | |
| 1809 | three functions are NULL, you need to call | |
| 1810 | png_set_progressive_read_fn(). You can use | |
| 1811 | any struct as the user_ptr (cast to a void pointer | |
| 1812 | for the function call), and retrieve the pointer | |
| 1813 | from inside the callbacks using the function | |
| 1814 | ||
| 1815 | png_get_progressive_ptr(png_ptr); | |
| 1816 | ||
| 1817 | which will return a void pointer, which you have | |
| 1818 | to cast appropriately. | |
| 1819 | */ | |
| 1820 | png_set_progressive_read_fn(png_ptr, (void *)user_ptr, | |
| 1821 | info_callback, row_callback, end_callback); | |
| 1822 | ||
| 1823 | return 0; | |
| 1824 | } | |
| 1825 | ||
| 1826 | /* A code fragment that you call as you receive blocks | |
| 1827 | of data */ | |
| 1828 | int | |
| 1829 | process_data(png_bytep buffer, png_uint_32 length) | |
| 1830 | { | |
| 1831 | if (setjmp(png_jmpbuf(png_ptr))) | |
| 1832 | { | |
| 1833 | png_destroy_read_struct(&png_ptr, &info_ptr, | |
| 1834 | (png_infopp)NULL); | |
| 1835 | return (ERROR); | |
| 1836 | } | |
| 1837 | ||
| 1838 | /* This one's new also. Simply give it a chunk | |
| 1839 | of data from the file stream (in order, of | |
| 1840 | course). On machines with segmented memory | |
| 1841 | models machines, don't give it any more than | |
| 1842 | 64K. The library seems to run fine with sizes | |
| 1843 | of 4K. Although you can give it much less if | |
| 1844 | necessary (I assume you can give it chunks of | |
| 1845 | 1 byte, I haven't tried less then 256 bytes | |
| 1846 | yet). When this function returns, you may | |
| 1847 | want to display any rows that were generated | |
| 1848 | in the row callback if you don't already do | |
| 1849 | so there. | |
| 1850 | */ | |
| 1851 | png_process_data(png_ptr, info_ptr, buffer, length); | |
| 1852 | return 0; | |
| 1853 | } | |
| 1854 | ||
| 1855 | /* This function is called (as set by | |
| 1856 | png_set_progressive_read_fn() above) when enough data | |
| 1857 | has been supplied so all of the header has been | |
| 1858 | read. | |
| 1859 | */ | |
| 1860 | void | |
| 1861 | info_callback(png_structp png_ptr, png_infop info) | |
| 1862 | { | |
| 1863 | /* Do any setup here, including setting any of | |
| 1864 | the transformations mentioned in the Reading | |
| 1865 | PNG files section. For now, you _must_ call | |
| 1866 | either png_start_read_image() or | |
| 1867 | png_read_update_info() after all the | |
| 1868 | transformations are set (even if you don't set | |
| 1869 | any). You may start getting rows before | |
| 1870 | png_process_data() returns, so this is your | |
| 1871 | last chance to prepare for that. | |
| 1872 | */ | |
| 1873 | } | |
| 1874 | ||
| 1875 | /* This function is called when each row of image | |
| 1876 | data is complete */ | |
| 1877 | void | |
| 1878 | row_callback(png_structp png_ptr, png_bytep new_row, | |
| 1879 | png_uint_32 row_num, int pass) | |
| 1880 | { | |
| 1881 | /* If the image is interlaced, and you turned | |
| 1882 | on the interlace handler, this function will | |
| 1883 | be called for every row in every pass. Some | |
| 1884 | of these rows will not be changed from the | |
| 1885 | previous pass. When the row is not changed, | |
| 1886 | the new_row variable will be NULL. The rows | |
| 1887 | and passes are called in order, so you don't | |
| 1888 | really need the row_num and pass, but I'm | |
| 1889 | supplying them because it may make your life | |
| 1890 | easier. | |
| 1891 | ||
| 1892 | For the non-NULL rows of interlaced images, | |
| 1893 | you must call png_progressive_combine_row() | |
| 1894 | passing in the row and the old row. You can | |
| 1895 | call this function for NULL rows (it will just | |
| 1896 | return) and for non-interlaced images (it just | |
| 1897 | does the memcpy for you) if it will make the | |
| 1898 | code easier. Thus, you can just do this for | |
| 1899 | all cases: | |
| 1900 | */ | |
| 1901 | ||
| 1902 | png_progressive_combine_row(png_ptr, old_row, | |
| 1903 | new_row); | |
| 1904 | ||
| 1905 | /* where old_row is what was displayed for | |
| 1906 | previously for the row. Note that the first | |
| 1907 | pass (pass == 0, really) will completely cover | |
| 1908 | the old row, so the rows do not have to be | |
| 1909 | initialized. After the first pass (and only | |
| 1910 | for interlaced images), you will have to pass | |
| 1911 | the current row, and the function will combine | |
| 1912 | the old row and the new row. | |
| 1913 | */ | |
| 1914 | } | |
| 1915 | ||
| 1916 | void | |
| 1917 | end_callback(png_structp png_ptr, png_infop info) | |
| 1918 | { | |
| 1919 | /* This function is called after the whole image | |
| 1920 | has been read, including any chunks after the | |
| 1921 | image (up to and including the IEND). You | |
| 1922 | will usually have the same info chunk as you | |
| 1923 | had in the header, although some data may have | |
| 1924 | been added to the comments and time fields. | |
| 1925 | ||
| 1926 | Most people won't do much here, perhaps setting | |
| 1927 | a flag that marks the image as finished. | |
| 1928 | */ | |
| 1929 | } | |
| 1930 | ||
| 1931 | ||
| 1932 | ||
| 1933 | .SH IV. Writing | |
| 1934 | ||
| 1935 | Much of this is very similar to reading. However, everything of | |
| 1936 | importance is repeated here, so you won't have to constantly look | |
| 1937 | back up in the reading section to understand writing. | |
| 1938 | ||
| 1939 | .SS Setup | |
| 1940 | ||
| 1941 | You will want to do the I/O initialization before you get into libpng, | |
| 1942 | so if it doesn't work, you don't have anything to undo. If you are not | |
| 1943 | using the standard I/O functions, you will need to replace them with | |
| 1944 | custom writing functions. See the discussion under Customizing libpng. | |
| 1945 | ||
| 1946 | FILE *fp = fopen(file_name, "wb"); | |
| 1947 | if (!fp) | |
| 1948 | { | |
| 1949 | return (ERROR); | |
| 1950 | } | |
| 1951 | ||
| 1952 | Next, png_struct and png_info need to be allocated and initialized. | |
| 1953 | As these can be both relatively large, you may not want to store these | |
| 1954 | on the stack, unless you have stack space to spare. Of course, you | |
| 1955 | will want to check if they return NULL. If you are also reading, | |
| 1956 | you won't want to name your read structure and your write structure | |
| 1957 | both "png_ptr"; you can call them anything you like, such as | |
| 1958 | "read_ptr" and "write_ptr". Look at pngtest.c, for example. | |
| 1959 | ||
| 1960 | png_structp png_ptr = png_create_write_struct | |
| 1961 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, | |
| 1962 | user_error_fn, user_warning_fn); | |
| 1963 | if (!png_ptr) | |
| 1964 | return (ERROR); | |
| 1965 | ||
| 1966 | png_infop info_ptr = png_create_info_struct(png_ptr); | |
| 1967 | if (!info_ptr) | |
| 1968 | { | |
| 1969 | png_destroy_write_struct(&png_ptr, | |
| 1970 | (png_infopp)NULL); | |
| 1971 | return (ERROR); | |
| 1972 | } | |
| 1973 | ||
| 1974 | If you want to use your own memory allocation routines, | |
| 1975 | define PNG_USER_MEM_SUPPORTED and use | |
| 1976 | png_create_write_struct_2() instead of png_create_write_struct(): | |
| 1977 | ||
| 1978 | png_structp png_ptr = png_create_write_struct_2 | |
| 1979 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, | |
| 1980 | user_error_fn, user_warning_fn, (png_voidp) | |
| 1981 | user_mem_ptr, user_malloc_fn, user_free_fn); | |
| 1982 | ||
| 1983 | After you have these structures, you will need to set up the | |
| 1984 | error handling. When libpng encounters an error, it expects to | |
| 1985 | longjmp() back to your routine. Therefore, you will need to call | |
| 1986 | setjmp() and pass the png_jmpbuf(png_ptr). If you | |
| 1987 | write the file from different routines, you will need to update | |
| 1988 | the png_jmpbuf(png_ptr) every time you enter a new routine that will | |
| 1989 | call a png_*() function. See your documentation of setjmp/longjmp | |
| 1990 | for your compiler for more information on setjmp/longjmp. See | |
| 1991 | the discussion on libpng error handling in the Customizing Libpng | |
| 1992 | section below for more information on the libpng error handling. | |
| 1993 | ||
| 1994 | if (setjmp(png_jmpbuf(png_ptr))) | |
| 1995 | { | |
| 1996 | png_destroy_write_struct(&png_ptr, &info_ptr); | |
| 1997 | fclose(fp); | |
| 1998 | return (ERROR); | |
| 1999 | } | |
| 2000 | ... | |
| 2001 | return; | |
| 2002 | ||
| 2003 | If you would rather avoid the complexity of setjmp/longjmp issues, | |
| 2004 | you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case | |
| 2005 | errors will result in a call to PNG_ABORT() which defaults to abort(). | |
| 2006 | ||
| 2007 | Now you need to set up the output code. The default for libpng is to | |
| 2008 | use the C function fwrite(). If you use this, you will need to pass a | |
| 2009 | valid FILE * in the function png_init_io(). Be sure that the file is | |
| 2010 | opened in binary mode. Again, if you wish to handle writing data in | |
| 2011 | another way, see the discussion on libpng I/O handling in the Customizing | |
| 2012 | Libpng section below. | |
| 2013 | ||
| 2014 | png_init_io(png_ptr, fp); | |
| 2015 | ||
| 2016 | If you are embedding your PNG into a datastream such as MNG, and don't | |
| 2017 | want libpng to write the 8-byte signature, or if you have already | |
| 2018 | written the signature in your application, use | |
| 2019 | ||
| 2020 | png_set_sig_bytes(png_ptr, 8); | |
| 2021 | ||
| 2022 | to inform libpng that it should not write a signature. | |
| 2023 | ||
| 2024 | .SS Write callbacks | |
| 2025 | ||
| 2026 | At this point, you can set up a callback function that will be | |
| 2027 | called after each row has been written, which you can use to control | |
| 2028 | a progress meter or the like. It's demonstrated in pngtest.c. | |
| 2029 | You must supply a function | |
| 2030 | ||
| 2031 | void write_row_callback(png_ptr, png_uint_32 row, | |
| 2032 | int pass); | |
| 2033 | { | |
| 2034 | /* put your code here */ | |
| 2035 | } | |
| 2036 | ||
| 2037 | (You can give it another name that you like instead of "write_row_callback") | |
| 2038 | ||
| 2039 | To inform libpng about your function, use | |
| 2040 | ||
| 2041 | png_set_write_status_fn(png_ptr, write_row_callback); | |
| 2042 | ||
| 2043 | You now have the option of modifying how the compression library will | |
| 2044 | run. The following functions are mainly for testing, but may be useful | |
| 2045 | in some cases, like if you need to write PNG files extremely fast and | |
| 2046 | are willing to give up some compression, or if you want to get the | |
| 2047 | maximum possible compression at the expense of slower writing. If you | |
| 2048 | have no special needs in this area, let the library do what it wants by | |
| 2049 | not calling this function at all, as it has been tuned to deliver a good | |
| 2050 | speed/compression ratio. The second parameter to png_set_filter() is | |
| 2051 | the filter method, for which the only valid values are 0 (as of the | |
| 2052 | July 1999 PNG specification, version 1.2) or 64 (if you are writing | |
| 2053 | a PNG datastream that is to be embedded in a MNG datastream). The third | |
| 2054 | parameter is a flag that indicates which filter type(s) are to be tested | |
| 2055 | for each scanline. See the PNG specification for details on the specific filter | |
| 2056 | types. | |
| 2057 | ||
| 2058 | ||
| 2059 | /* turn on or off filtering, and/or choose | |
| 2060 | specific filters. You can use either a single | |
| 2061 | PNG_FILTER_VALUE_NAME or the bitwise OR of one | |
| 2062 | or more PNG_FILTER_NAME masks. */ | |
| 2063 | png_set_filter(png_ptr, 0, | |
| 2064 | PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE | | |
| 2065 | PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB | | |
| 2066 | PNG_FILTER_UP | PNG_FILTER_VALUE_UP | | |
| 2067 | PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE | | |
| 2068 | PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH| | |
| 2069 | PNG_ALL_FILTERS); | |
| 2070 | ||
| 2071 | If an application | |
| 2072 | wants to start and stop using particular filters during compression, | |
| 2073 | it should start out with all of the filters (to ensure that the previous | |
| 2074 | row of pixels will be stored in case it's needed later), and then add | |
| 2075 | and remove them after the start of compression. | |
| 2076 | ||
| 2077 | If you are writing a PNG datastream that is to be embedded in a MNG | |
| 2078 | datastream, the second parameter can be either 0 or 64. | |
| 2079 | ||
| 2080 | The png_set_compression_*() functions interface to the zlib compression | |
| 2081 | library, and should mostly be ignored unless you really know what you are | |
| 2082 | doing. The only generally useful call is png_set_compression_level() | |
| 2083 | which changes how much time zlib spends on trying to compress the image | |
| 2084 | data. See the Compression Library (zlib.h and algorithm.txt, distributed | |
| 2085 | with zlib) for details on the compression levels. | |
| 2086 | ||
| 2087 | /* set the zlib compression level */ | |
| 2088 | png_set_compression_level(png_ptr, | |
| 2089 | Z_BEST_COMPRESSION); | |
| 2090 | ||
| 2091 | /* set other zlib parameters */ | |
| 2092 | png_set_compression_mem_level(png_ptr, 8); | |
| 2093 | png_set_compression_strategy(png_ptr, | |
| 2094 | Z_DEFAULT_STRATEGY); | |
| 2095 | png_set_compression_window_bits(png_ptr, 15); | |
| 2096 | png_set_compression_method(png_ptr, 8); | |
| 2097 | png_set_compression_buffer_size(png_ptr, 8192) | |
| 2098 | ||
| 2099 | extern PNG_EXPORT(void,png_set_zbuf_size) | |
| 2100 | ||
| 2101 | .SS Setting the contents of info for output | |
| 2102 | ||
| 2103 | You now need to fill in the png_info structure with all the data you | |
| 2104 | wish to write before the actual image. Note that the only thing you | |
| 2105 | are allowed to write after the image is the text chunks and the time | |
| 2106 | chunk (as of PNG Specification 1.2, anyway). See png_write_end() and | |
| 2107 | the latest PNG specification for more information on that. If you | |
| 2108 | wish to write them before the image, fill them in now, and flag that | |
| 2109 | data as being valid. If you want to wait until after the data, don't | |
| 2110 | fill them until png_write_end(). For all the fields in png_info and | |
| 2111 | their data types, see png.h. For explanations of what the fields | |
| 2112 | contain, see the PNG specification. | |
| 2113 | ||
| 2114 | Some of the more important parts of the png_info are: | |
| 2115 | ||
| 2116 | png_set_IHDR(png_ptr, info_ptr, width, height, | |
| 2117 | bit_depth, color_type, interlace_type, | |
| 2118 | compression_type, filter_method) | |
| 2119 | width - holds the width of the image | |
| 2120 | in pixels (up to 2^31). | |
| 2121 | height - holds the height of the image | |
| 2122 | in pixels (up to 2^31). | |
| 2123 | bit_depth - holds the bit depth of one of the | |
| 2124 | image channels. | |
| 2125 | (valid values are 1, 2, 4, 8, 16 | |
| 2126 | and depend also on the | |
| 2127 | color_type. See also significant | |
| 2128 | bits (sBIT) below). | |
| 2129 | color_type - describes which color/alpha | |
| 2130 | channels are present. | |
| 2131 | PNG_COLOR_TYPE_GRAY | |
| 2132 | (bit depths 1, 2, 4, 8, 16) | |
| 2133 | PNG_COLOR_TYPE_GRAY_ALPHA | |
| 2134 | (bit depths 8, 16) | |
| 2135 | PNG_COLOR_TYPE_PALETTE | |
| 2136 | (bit depths 1, 2, 4, 8) | |
| 2137 | PNG_COLOR_TYPE_RGB | |
| 2138 | (bit_depths 8, 16) | |
| 2139 | PNG_COLOR_TYPE_RGB_ALPHA | |
| 2140 | (bit_depths 8, 16) | |
| 2141 | ||
| 2142 | PNG_COLOR_MASK_PALETTE | |
| 2143 | PNG_COLOR_MASK_COLOR | |
| 2144 | PNG_COLOR_MASK_ALPHA | |
| 2145 | ||
| 2146 | interlace_type - PNG_INTERLACE_NONE or | |
| 2147 | PNG_INTERLACE_ADAM7 | |
| 2148 | compression_type - (must be | |
| 2149 | PNG_COMPRESSION_TYPE_DEFAULT) | |
| 2150 | filter_method - (must be PNG_FILTER_TYPE_DEFAULT | |
| 2151 | or, if you are writing a PNG to | |
| 2152 | be embedded in a MNG datastream, | |
| 2153 | can also be | |
| 2154 | PNG_INTRAPIXEL_DIFFERENCING) | |
| 2155 | ||
| 2156 | png_set_PLTE(png_ptr, info_ptr, palette, | |
| 2157 | num_palette); | |
| 2158 | palette - the palette for the file | |
| 2159 | (array of png_color) | |
| 2160 | num_palette - number of entries in the palette | |
| 2161 | ||
| 2162 | png_set_gAMA(png_ptr, info_ptr, gamma); | |
| 2163 | gamma - the gamma the image was created | |
| 2164 | at (PNG_INFO_gAMA) | |
| 2165 | ||
| 2166 | png_set_sRGB(png_ptr, info_ptr, srgb_intent); | |
| 2167 | srgb_intent - the rendering intent | |
| 2168 | (PNG_INFO_sRGB) The presence of | |
| 2169 | the sRGB chunk means that the pixel | |
| 2170 | data is in the sRGB color space. | |
| 2171 | This chunk also implies specific | |
| 2172 | values of gAMA and cHRM. Rendering | |
| 2173 | intent is the CSS-1 property that | |
| 2174 | has been defined by the International | |
| 2175 | Color Consortium | |
| 2176 | (http://www.color.org). | |
| 2177 | It can be one of | |
| 2178 | PNG_sRGB_INTENT_SATURATION, | |
| 2179 | PNG_sRGB_INTENT_PERCEPTUAL, | |
| 2180 | PNG_sRGB_INTENT_ABSOLUTE, or | |
| 2181 | PNG_sRGB_INTENT_RELATIVE. | |
| 2182 | ||
| 2183 | ||
| 2184 | png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr, | |
| 2185 | srgb_intent); | |
| 2186 | srgb_intent - the rendering intent | |
| 2187 | (PNG_INFO_sRGB) The presence of the | |
| 2188 | sRGB chunk means that the pixel | |
| 2189 | data is in the sRGB color space. | |
| 2190 | This function also causes gAMA and | |
| 2191 | cHRM chunks with the specific values | |
| 2192 | that are consistent with sRGB to be | |
| 2193 | written. | |
| 2194 | ||
| 2195 | png_set_iCCP(png_ptr, info_ptr, name, compression_type, | |
| 2196 | profile, proflen); | |
| 2197 | name - The profile name. | |
| 2198 | compression - The compression type; always | |
| 2199 | PNG_COMPRESSION_TYPE_BASE for PNG 1.0. | |
| 2200 | You may give NULL to this argument to | |
| 2201 | ignore it. | |
| 2202 | profile - International Color Consortium color | |
| 2203 | profile data. May contain NULs. | |
| 2204 | proflen - length of profile data in bytes. | |
| 2205 | ||
| 2206 | png_set_sBIT(png_ptr, info_ptr, sig_bit); | |
| 2207 | sig_bit - the number of significant bits for | |
| 2208 | (PNG_INFO_sBIT) each of the gray, red, | |
| 2209 | green, and blue channels, whichever are | |
| 2210 | appropriate for the given color type | |
| 2211 | (png_color_16) | |
| 2212 | ||
| 2213 | png_set_tRNS(png_ptr, info_ptr, trans, num_trans, | |
| 2214 | trans_values); | |
| 2215 | trans - array of transparent entries for | |
| 2216 | palette (PNG_INFO_tRNS) | |
| 2217 | trans_values - graylevel or color sample values of | |
| 2218 | the single transparent color for | |
| 2219 | non-paletted images (PNG_INFO_tRNS) | |
| 2220 | num_trans - number of transparent entries | |
| 2221 | (PNG_INFO_tRNS) | |
| 2222 | ||
| 2223 | png_set_hIST(png_ptr, info_ptr, hist); | |
| 2224 | (PNG_INFO_hIST) | |
| 2225 | hist - histogram of palette (array of | |
| 2226 | png_uint_16) | |
| 2227 | ||
| 2228 | png_set_tIME(png_ptr, info_ptr, mod_time); | |
| 2229 | mod_time - time image was last modified | |
| 2230 | (PNG_VALID_tIME) | |
| 2231 | ||
| 2232 | png_set_bKGD(png_ptr, info_ptr, background); | |
| 2233 | background - background color (PNG_VALID_bKGD) | |
| 2234 | ||
| 2235 | png_set_text(png_ptr, info_ptr, text_ptr, num_text); | |
| 2236 | text_ptr - array of png_text holding image | |
| 2237 | comments | |
| 2238 | text_ptr[i].compression - type of compression used | |
| 2239 | on "text" PNG_TEXT_COMPRESSION_NONE | |
| 2240 | PNG_TEXT_COMPRESSION_zTXt | |
| 2241 | PNG_ITXT_COMPRESSION_NONE | |
| 2242 | PNG_ITXT_COMPRESSION_zTXt | |
| 2243 | text_ptr[i].key - keyword for comment. Must contain | |
| 2244 | 1-79 characters. | |
| 2245 | text_ptr[i].text - text comments for current | |
| 2246 | keyword. Can be NULL or empty. | |
| 2247 | text_ptr[i].text_length - length of text string, | |
| 2248 | after decompression, 0 for iTXt | |
| 2249 | text_ptr[i].itxt_length - length of itxt string, | |
| 2250 | after decompression, 0 for tEXt/zTXt | |
| 2251 | text_ptr[i].lang - language of comment (NULL or | |
| 2252 | empty for unknown). | |
| 2253 | text_ptr[i].translated_keyword - keyword in UTF-8 (NULL | |
| 2254 | or empty for unknown). | |
| 2255 | num_text - number of comments | |
| 2256 | ||
| 2257 | png_set_sPLT(png_ptr, info_ptr, &palette_ptr, | |
| 2258 | num_spalettes); | |
| 2259 | palette_ptr - array of png_sPLT_struct structures | |
| 2260 | to be added to the list of palettes | |
| 2261 | in the info structure. | |
| 2262 | num_spalettes - number of palette structures to be | |
| 2263 | added. | |
| 2264 | ||
| 2265 | png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y, | |
| 2266 | unit_type); | |
| 2267 | offset_x - positive offset from the left | |
| 2268 | edge of the screen | |
| 2269 | offset_y - positive offset from the top | |
| 2270 | edge of the screen | |
| 2271 | unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER | |
| 2272 | ||
| 2273 | png_set_pHYs(png_ptr, info_ptr, res_x, res_y, | |
| 2274 | unit_type); | |
| 2275 | res_x - pixels/unit physical resolution | |
| 2276 | in x direction | |
| 2277 | res_y - pixels/unit physical resolution | |
| 2278 | in y direction | |
| 2279 | unit_type - PNG_RESOLUTION_UNKNOWN, | |
| 2280 | PNG_RESOLUTION_METER | |
| 2281 | ||
| 2282 | png_set_sCAL(png_ptr, info_ptr, unit, width, height) | |
| 2283 | unit - physical scale units (an integer) | |
| 2284 | width - width of a pixel in physical scale units | |
| 2285 | height - height of a pixel in physical scale units | |
| 2286 | (width and height are doubles) | |
| 2287 | ||
| 2288 | png_set_sCAL_s(png_ptr, info_ptr, unit, width, height) | |
| 2289 | unit - physical scale units (an integer) | |
| 2290 | width - width of a pixel in physical scale units | |
| 2291 | height - height of a pixel in physical scale units | |
| 2292 | (width and height are strings like "2.54") | |
| 2293 | ||
| 2294 | png_set_unknown_chunks(png_ptr, info_ptr, &unknowns, | |
| 2295 | num_unknowns) | |
| 2296 | unknowns - array of png_unknown_chunk | |
| 2297 | structures holding unknown chunks | |
| 2298 | unknowns[i].name - name of unknown chunk | |
| 2299 | unknowns[i].data - data of unknown chunk | |
| 2300 | unknowns[i].size - size of unknown chunk's data | |
| 2301 | unknowns[i].location - position to write chunk in file | |
| 2302 | 0: do not write chunk | |
| 2303 | PNG_HAVE_IHDR: before PLTE | |
| 2304 | PNG_HAVE_PLTE: before IDAT | |
| 2305 | PNG_AFTER_IDAT: after IDAT | |
| 2306 | ||
| 2307 | The "location" member is set automatically according to | |
| 2308 | what part of the output file has already been written. | |
| 2309 | You can change its value after calling png_set_unknown_chunks() | |
| 2310 | as demonstrated in pngtest.c. Within each of the "locations", | |
| 2311 | the chunks are sequenced according to their position in the | |
| 2312 | structure (that is, the value of "i", which is the order in which | |
| 2313 | the chunk was either read from the input file or defined with | |
| 2314 | png_set_unknown_chunks). | |
| 2315 | ||
| 2316 | A quick word about text and num_text. text is an array of png_text | |
| 2317 | structures. num_text is the number of valid structures in the array. | |
| 2318 | Each png_text structure holds a language code, a keyword, a text value, | |
| 2319 | and a compression type. | |
| 2320 | ||
| 2321 | The compression types have the same valid numbers as the compression | |
| 2322 | types of the image data. Currently, the only valid number is zero. | |
| 2323 | However, you can store text either compressed or uncompressed, unlike | |
| 2324 | images, which always have to be compressed. So if you don't want the | |
| 2325 | text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE. | |
| 2326 | Because tEXt and zTXt chunks don't have a language field, if you | |
| 2327 | specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt | |
| 2328 | any language code or translated keyword will not be written out. | |
| 2329 | ||
| 2330 | Until text gets around 1000 bytes, it is not worth compressing it. | |
| 2331 | After the text has been written out to the file, the compression type | |
| 2332 | is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR, | |
| 2333 | so that it isn't written out again at the end (in case you are calling | |
| 2334 | png_write_end() with the same struct. | |
| 2335 | ||
| 2336 | The keywords that are given in the PNG Specification are: | |
| 2337 | ||
| 2338 | Title Short (one line) title or | |
| 2339 | caption for image | |
| 2340 | Author Name of image's creator | |
| 2341 | Description Description of image (possibly long) | |
| 2342 | Copyright Copyright notice | |
| 2343 | Creation Time Time of original image creation | |
| 2344 | (usually RFC 1123 format, see below) | |
| 2345 | Software Software used to create the image | |
| 2346 | Disclaimer Legal disclaimer | |
| 2347 | Warning Warning of nature of content | |
| 2348 | Source Device used to create the image | |
| 2349 | Comment Miscellaneous comment; conversion | |
| 2350 | from other image format | |
| 2351 | ||
| 2352 | The keyword-text pairs work like this. Keywords should be short | |
| 2353 | simple descriptions of what the comment is about. Some typical | |
| 2354 | keywords are found in the PNG specification, as is some recommendations | |
| 2355 | on keywords. You can repeat keywords in a file. You can even write | |
| 2356 | some text before the image and some after. For example, you may want | |
| 2357 | to put a description of the image before the image, but leave the | |
| 2358 | disclaimer until after, so viewers working over modem connections | |
| 2359 | don't have to wait for the disclaimer to go over the modem before | |
| 2360 | they start seeing the image. Finally, keywords should be full | |
| 2361 | words, not abbreviations. Keywords and text are in the ISO 8859-1 | |
| 2362 | (Latin-1) character set (a superset of regular ASCII) and can not | |
| 2363 | contain NUL characters, and should not contain control or other | |
| 2364 | unprintable characters. To make the comments widely readable, stick | |
| 2365 | with basic ASCII, and avoid machine specific character set extensions | |
| 2366 | like the IBM-PC character set. The keyword must be present, but | |
| 2367 | you can leave off the text string on non-compressed pairs. | |
| 2368 | Compressed pairs must have a text string, as only the text string | |
| 2369 | is compressed anyway, so the compression would be meaningless. | |
| 2370 | ||
| 2371 | PNG supports modification time via the png_time structure. Two | |
| 2372 | conversion routines are provided, png_convert_from_time_t() for | |
| 2373 | time_t and png_convert_from_struct_tm() for struct tm. The | |
| 2374 | time_t routine uses gmtime(). You don't have to use either of | |
| 2375 | these, but if you wish to fill in the png_time structure directly, | |
| 2376 | you should provide the time in universal time (GMT) if possible | |
| 2377 | instead of your local time. Note that the year number is the full | |
| 2378 | year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and | |
| 2379 | that months start with 1. | |
| 2380 | ||
| 2381 | If you want to store the time of the original image creation, you should | |
| 2382 | use a plain tEXt chunk with the "Creation Time" keyword. This is | |
| 2383 | necessary because the "creation time" of a PNG image is somewhat vague, | |
| 2384 | depending on whether you mean the PNG file, the time the image was | |
| 2385 | created in a non-PNG format, a still photo from which the image was | |
| 2386 | scanned, or possibly the subject matter itself. In order to facilitate | |
| 2387 | machine-readable dates, it is recommended that the "Creation Time" | |
| 2388 | tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"), | |
| 2389 | although this isn't a requirement. Unlike the tIME chunk, the | |
| 2390 | "Creation Time" tEXt chunk is not expected to be automatically changed | |
| 2391 | by the software. To facilitate the use of RFC 1123 dates, a function | |
| 2392 | png_convert_to_rfc1123(png_timep) is provided to convert from PNG | |
| 2393 | time to an RFC 1123 format string. | |
| 2394 | ||
| 2395 | .SS Writing unknown chunks | |
| 2396 | ||
| 2397 | You can use the png_set_unknown_chunks function to queue up chunks | |
| 2398 | for writing. You give it a chunk name, raw data, and a size; that's | |
| 2399 | all there is to it. The chunks will be written by the next following | |
| 2400 | png_write_info_before_PLTE, png_write_info, or png_write_end function. | |
| 2401 | Any chunks previously read into the info structure's unknown-chunk | |
| 2402 | list will also be written out in a sequence that satisfies the PNG | |
| 2403 | specification's ordering rules. | |
| 2404 | ||
| 2405 | .SS The high-level write interface | |
| 2406 | ||
| 2407 | At this point there are two ways to proceed; through the high-level | |
| 2408 | write interface, or through a sequence of low-level write operations. | |
| 2409 | You can use the high-level interface if your image data is present | |
| 2410 | in the info structure. All defined output | |
| 2411 | transformations are permitted, enabled by the following masks. | |
| 2412 | ||
| 2413 | PNG_TRANSFORM_IDENTITY No transformation | |
| 2414 | PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples | |
| 2415 | PNG_TRANSFORM_PACKSWAP Change order of packed | |
| 2416 | pixels to LSB first | |
| 2417 | PNG_TRANSFORM_INVERT_MONO Invert monochrome images | |
| 2418 | PNG_TRANSFORM_SHIFT Normalize pixels to the | |
| 2419 | sBIT depth | |
| 2420 | PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA | |
| 2421 | to BGRA | |
| 2422 | PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA | |
| 2423 | to AG | |
| 2424 | PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity | |
| 2425 | to transparency | |
| 2426 | PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples | |
| 2427 | PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes. | |
| 2428 | ||
| 2429 | If you have valid image data in the info structure (you can use | |
| 2430 | png_set_rows() to put image data in the info structure), simply do this: | |
| 2431 | ||
| 2432 | png_write_png(png_ptr, info_ptr, png_transforms, NULL) | |
| 2433 | ||
| 2434 | where png_transforms is an integer containing the bitwise OR of some set of | |
| 2435 | transformation flags. This call is equivalent to png_write_info(), | |
| 2436 | followed the set of transformations indicated by the transform mask, | |
| 2437 | then png_write_image(), and finally png_write_end(). | |
| 2438 | ||
| 2439 | (The final parameter of this call is not yet used. Someday it might point | |
| 2440 | to transformation parameters required by some future output transform.) | |
| 2441 | ||
| 2442 | You must use png_transforms and not call any png_set_transform() functions | |
| 2443 | when you use png_write_png(). | |
| 2444 | ||
| 2445 | .SS The low-level write interface | |
| 2446 | ||
| 2447 | If you are going the low-level route instead, you are now ready to | |
| 2448 | write all the file information up to the actual image data. You do | |
| 2449 | this with a call to png_write_info(). | |
| 2450 | ||
| 2451 | png_write_info(png_ptr, info_ptr); | |
| 2452 | ||
| 2453 | Note that there is one transformation you may need to do before | |
| 2454 | png_write_info(). In PNG files, the alpha channel in an image is the | |
| 2455 | level of opacity. If your data is supplied as a level of | |
| 2456 | transparency, you can invert the alpha channel before you write it, so | |
| 2457 | that 0 is fully transparent and 255 (in 8-bit or paletted images) or | |
| 2458 | 65535 (in 16-bit images) is fully opaque, with | |
| 2459 | ||
| 2460 | png_set_invert_alpha(png_ptr); | |
| 2461 | ||
| 2462 | This must appear before png_write_info() instead of later with the | |
| 2463 | other transformations because in the case of paletted images the tRNS | |
| 2464 | chunk data has to be inverted before the tRNS chunk is written. If | |
| 2465 | your image is not a paletted image, the tRNS data (which in such cases | |
| 2466 | represents a single color to be rendered as transparent) won't need to | |
| 2467 | be changed, and you can safely do this transformation after your | |
| 2468 | png_write_info() call. | |
| 2469 | ||
| 2470 | If you need to write a private chunk that you want to appear before | |
| 2471 | the PLTE chunk when PLTE is present, you can write the PNG info in | |
| 2472 | two steps, and insert code to write your own chunk between them: | |
| 2473 | ||
| 2474 | png_write_info_before_PLTE(png_ptr, info_ptr); | |
| 2475 | png_set_unknown_chunks(png_ptr, info_ptr, ...); | |
| 2476 | png_write_info(png_ptr, info_ptr); | |
| 2477 | ||
| 2478 | After you've written the file information, you can set up the library | |
| 2479 | to handle any special transformations of the image data. The various | |
| 2480 | ways to transform the data will be described in the order that they | |
| 2481 | should occur. This is important, as some of these change the color | |
| 2482 | type and/or bit depth of the data, and some others only work on | |
| 2483 | certain color types and bit depths. Even though each transformation | |
| 2484 | checks to see if it has data that it can do something with, you should | |
| 2485 | make sure to only enable a transformation if it will be valid for the | |
| 2486 | data. For example, don't swap red and blue on grayscale data. | |
| 2487 | ||
| 2488 | PNG files store RGB pixels packed into 3 or 6 bytes. This code tells | |
| 2489 | the library to strip input data that has 4 or 8 bytes per pixel down | |
| 2490 | to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2 | |
| 2491 | bytes per pixel). | |
| 2492 | ||
| 2493 | png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE); | |
| 2494 | ||
| 2495 | where the 0 is unused, and the location is either PNG_FILLER_BEFORE or | |
| 2496 | PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel | |
| 2497 | is stored XRGB or RGBX. | |
| 2498 | ||
| 2499 | PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as | |
| 2500 | they can, resulting in, for example, 8 pixels per byte for 1 bit files. | |
| 2501 | If the data is supplied at 1 pixel per byte, use this code, which will | |
| 2502 | correctly pack the pixels into a single byte: | |
| 2503 | ||
| 2504 | png_set_packing(png_ptr); | |
| 2505 | ||
| 2506 | PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your | |
| 2507 | data is of another bit depth, you can write an sBIT chunk into the | |
| 2508 | file so that decoders can recover the original data if desired. | |
| 2509 | ||
| 2510 | /* Set the true bit depth of the image data */ | |
| 2511 | if (color_type & PNG_COLOR_MASK_COLOR) | |
| 2512 | { | |
| 2513 | sig_bit.red = true_bit_depth; | |
| 2514 | sig_bit.green = true_bit_depth; | |
| 2515 | sig_bit.blue = true_bit_depth; | |
| 2516 | } | |
| 2517 | else | |
| 2518 | { | |
| 2519 | sig_bit.gray = true_bit_depth; | |
| 2520 | } | |
| 2521 | if (color_type & PNG_COLOR_MASK_ALPHA) | |
| 2522 | { | |
| 2523 | sig_bit.alpha = true_bit_depth; | |
| 2524 | } | |
| 2525 | ||
| 2526 | png_set_sBIT(png_ptr, info_ptr, &sig_bit); | |
| 2527 | ||
| 2528 | If the data is stored in the row buffer in a bit depth other than | |
| 2529 | one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG), | |
| 2530 | this will scale the values to appear to be the correct bit depth as | |
| 2531 | is required by PNG. | |
| 2532 | ||
| 2533 | png_set_shift(png_ptr, &sig_bit); | |
| 2534 | ||
| 2535 | PNG files store 16 bit pixels in network byte order (big-endian, | |
| 2536 | ie. most significant bits first). This code would be used if they are | |
| 2537 | supplied the other way (little-endian, i.e. least significant bits | |
| 2538 | first, the way PCs store them): | |
| 2539 | ||
| 2540 | if (bit_depth > 8) | |
| 2541 | png_set_swap(png_ptr); | |
| 2542 | ||
| 2543 | If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you | |
| 2544 | need to change the order the pixels are packed into bytes, you can use: | |
| 2545 | ||
| 2546 | if (bit_depth < 8) | |
| 2547 | png_set_packswap(png_ptr); | |
| 2548 | ||
| 2549 | PNG files store 3 color pixels in red, green, blue order. This code | |
| 2550 | would be used if they are supplied as blue, green, red: | |
| 2551 | ||
| 2552 | png_set_bgr(png_ptr); | |
| 2553 | ||
| 2554 | PNG files describe monochrome as black being zero and white being | |
| 2555 | one. This code would be used if the pixels are supplied with this reversed | |
| 2556 | (black being one and white being zero): | |
| 2557 | ||
| 2558 | png_set_invert_mono(png_ptr); | |
| 2559 | ||
| 2560 | Finally, you can write your own transformation function if none of | |
| 2561 | the existing ones meets your needs. This is done by setting a callback | |
| 2562 | with | |
| 2563 | ||
| 2564 | png_set_write_user_transform_fn(png_ptr, | |
| 2565 | write_transform_fn); | |
| 2566 | ||
| 2567 | You must supply the function | |
| 2568 | ||
| 2569 | void write_transform_fn(png_ptr ptr, row_info_ptr | |
| 2570 | row_info, png_bytep data) | |
| 2571 | ||
| 2572 | See pngtest.c for a working example. Your function will be called | |
| 2573 | before any of the other transformations are processed. | |
| 2574 | ||
| 2575 | You can also set up a pointer to a user structure for use by your | |
| 2576 | callback function. | |
| 2577 | ||
| 2578 | png_set_user_transform_info(png_ptr, user_ptr, 0, 0); | |
| 2579 | ||
| 2580 | The user_channels and user_depth parameters of this function are ignored | |
| 2581 | when writing; you can set them to zero as shown. | |
| 2582 | ||
| 2583 | You can retrieve the pointer via the function png_get_user_transform_ptr(). | |
| 2584 | For example: | |
| 2585 | ||
| 2586 | voidp write_user_transform_ptr = | |
| 2587 | png_get_user_transform_ptr(png_ptr); | |
| 2588 | ||
| 2589 | It is possible to have libpng flush any pending output, either manually, | |
| 2590 | or automatically after a certain number of lines have been written. To | |
| 2591 | flush the output stream a single time call: | |
| 2592 | ||
| 2593 | png_write_flush(png_ptr); | |
| 2594 | ||
| 2595 | and to have libpng flush the output stream periodically after a certain | |
| 2596 | number of scanlines have been written, call: | |
| 2597 | ||
| 2598 | png_set_flush(png_ptr, nrows); | |
| 2599 | ||
| 2600 | Note that the distance between rows is from the last time png_write_flush() | |
| 2601 | was called, or the first row of the image if it has never been called. | |
| 2602 | So if you write 50 lines, and then png_set_flush 25, it will flush the | |
| 2603 | output on the next scanline, and every 25 lines thereafter, unless | |
| 2604 | png_write_flush() is called before 25 more lines have been written. | |
| 2605 | If nrows is too small (less than about 10 lines for a 640 pixel wide | |
| 2606 | RGB image) the image compression may decrease noticeably (although this | |
| 2607 | may be acceptable for real-time applications). Infrequent flushing will | |
| 2608 | only degrade the compression performance by a few percent over images | |
| 2609 | that do not use flushing. | |
| 2610 | ||
| 2611 | .SS Writing the image data | |
| 2612 | ||
| 2613 | That's it for the transformations. Now you can write the image data. | |
| 2614 | The simplest way to do this is in one function call. If you have the | |
| 2615 | whole image in memory, you can just call png_write_image() and libpng | |
| 2616 | will write the image. You will need to pass in an array of pointers to | |
| 2617 | each row. This function automatically handles interlacing, so you don't | |
| 2618 | need to call png_set_interlace_handling() or call this function multiple | |
| 2619 | times, or any of that other stuff necessary with png_write_rows(). | |
| 2620 | ||
| 2621 | png_write_image(png_ptr, row_pointers); | |
| 2622 | ||
| 2623 | where row_pointers is: | |
| 2624 | ||
| 2625 | png_byte *row_pointers[height]; | |
| 2626 | ||
| 2627 | You can point to void or char or whatever you use for pixels. | |
| 2628 | ||
| 2629 | If you don't want to write the whole image at once, you can | |
| 2630 | use png_write_rows() instead. If the file is not interlaced, | |
| 2631 | this is simple: | |
| 2632 | ||
| 2633 | png_write_rows(png_ptr, row_pointers, | |
| 2634 | number_of_rows); | |
| 2635 | ||
| 2636 | row_pointers is the same as in the png_write_image() call. | |
| 2637 | ||
| 2638 | If you are just writing one row at a time, you can do this with | |
| 2639 | a single row_pointer instead of an array of row_pointers: | |
| 2640 | ||
| 2641 | png_bytep row_pointer = row; | |
| 2642 | ||
| 2643 | png_write_row(png_ptr, row_pointer); | |
| 2644 | ||
| 2645 | When the file is interlaced, things can get a good deal more | |
| 2646 | complicated. The only currently (as of the PNG Specification | |
| 2647 | version 1.2, dated July 1999) defined interlacing scheme for PNG files | |
| 2648 | is the "Adam7" interlace scheme, that breaks down an | |
| 2649 | image into seven smaller images of varying size. libpng will build | |
| 2650 | these images for you, or you can do them yourself. If you want to | |
| 2651 | build them yourself, see the PNG specification for details of which | |
| 2652 | pixels to write when. | |
| 2653 | ||
| 2654 | If you don't want libpng to handle the interlacing details, just | |
| 2655 | use png_set_interlace_handling() and call png_write_rows() the | |
| 2656 | correct number of times to write all seven sub-images. | |
| 2657 | ||
| 2658 | If you want libpng to build the sub-images, call this before you start | |
| 2659 | writing any rows: | |
| 2660 | ||
| 2661 | number_of_passes = | |
| 2662 | png_set_interlace_handling(png_ptr); | |
| 2663 | ||
| 2664 | This will return the number of passes needed. Currently, this | |
| 2665 | is seven, but may change if another interlace type is added. | |
| 2666 | ||
| 2667 | Then write the complete image number_of_passes times. | |
| 2668 | ||
| 2669 | png_write_rows(png_ptr, row_pointers, | |
| 2670 | number_of_rows); | |
| 2671 | ||
| 2672 | As some of these rows are not used, and thus return immediately, | |
| 2673 | you may want to read about interlacing in the PNG specification, | |
| 2674 | and only update the rows that are actually used. | |
| 2675 | ||
| 2676 | .SS Finishing a sequential write | |
| 2677 | ||
| 2678 | After you are finished writing the image, you should finish writing | |
| 2679 | the file. If you are interested in writing comments or time, you should | |
| 2680 | pass an appropriately filled png_info pointer. If you are not interested, | |
| 2681 | you can pass NULL. | |
| 2682 | ||
| 2683 | png_write_end(png_ptr, info_ptr); | |
| 2684 | ||
| 2685 | When you are done, you can free all memory used by libpng like this: | |
| 2686 | ||
| 2687 | png_destroy_write_struct(&png_ptr, &info_ptr); | |
| 2688 | ||
| 2689 | It is also possible to individually free the info_ptr members that | |
| 2690 | point to libpng-allocated storage with the following function: | |
| 2691 | ||
| 2692 | png_free_data(png_ptr, info_ptr, mask, seq) | |
| 2693 | mask - identifies data to be freed, a mask | |
| 2694 | containing the bitwise OR of one or | |
| 2695 | more of | |
| 2696 | PNG_FREE_PLTE, PNG_FREE_TRNS, | |
| 2697 | PNG_FREE_HIST, PNG_FREE_ICCP, | |
| 2698 | PNG_FREE_PCAL, PNG_FREE_ROWS, | |
| 2699 | PNG_FREE_SCAL, PNG_FREE_SPLT, | |
| 2700 | PNG_FREE_TEXT, PNG_FREE_UNKN, | |
| 2701 | or simply PNG_FREE_ALL | |
| 2702 | seq - sequence number of item to be freed | |
| 2703 | (-1 for all items) | |
| 2704 | ||
| 2705 | This function may be safely called when the relevant storage has | |
| 2706 | already been freed, or has not yet been allocated, or was allocated | |
| 2707 | by the user and not by libpng, and will in those | |
| 2708 | cases do nothing. The "seq" parameter is ignored if only one item | |
| 2709 | of the selected data type, such as PLTE, is allowed. If "seq" is not | |
| 2710 | -1, and multiple items are allowed for the data type identified in | |
| 2711 | the mask, such as text or sPLT, only the n'th item in the structure | |
| 2712 | is freed, where n is "seq". | |
| 2713 | ||
| 2714 | If you allocated data such as a palette that you passed | |
| 2715 | in to libpng with png_set_*, you must not free it until just before the call to | |
| 2716 | png_destroy_write_struct(). | |
| 2717 | ||
| 2718 | The default behavior is only to free data that was allocated internally | |
| 2719 | by libpng. This can be changed, so that libpng will not free the data, | |
| 2720 | or so that it will free data that was allocated by the user with png_malloc() | |
| 2721 | or png_zalloc() and passed in via a png_set_*() function, with | |
| 2722 | ||
| 2723 | png_data_freer(png_ptr, info_ptr, freer, mask) | |
| 2724 | mask - which data elements are affected | |
| 2725 | same choices as in png_free_data() | |
| 2726 | freer - one of | |
| 2727 | PNG_DESTROY_WILL_FREE_DATA | |
| 2728 | PNG_SET_WILL_FREE_DATA | |
| 2729 | PNG_USER_WILL_FREE_DATA | |
| 2730 | ||
| 2731 | For example, to transfer responsibility for some data from a read structure | |
| 2732 | to a write structure, you could use | |
| 2733 | ||
| 2734 | png_data_freer(read_ptr, read_info_ptr, | |
| 2735 | PNG_USER_WILL_FREE_DATA, | |
| 2736 | PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST) | |
| 2737 | png_data_freer(write_ptr, write_info_ptr, | |
| 2738 | PNG_DESTROY_WILL_FREE_DATA, | |
| 2739 | PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST) | |
| 2740 | ||
| 2741 | thereby briefly reassigning responsibility for freeing to the user but | |
| 2742 | immediately afterwards reassigning it once more to the write_destroy | |
| 2743 | function. Having done this, it would then be safe to destroy the read | |
| 2744 | structure and continue to use the PLTE, tRNS, and hIST data in the write | |
| 2745 | structure. | |
| 2746 | ||
| 2747 | This function only affects data that has already been allocated. | |
| 2748 | You can call this function before calling after the png_set_*() functions | |
| 2749 | to control whether the user or png_destroy_*() is supposed to free the data. | |
| 2750 | When the user assumes responsibility for libpng-allocated data, the | |
| 2751 | application must use | |
| 2752 | png_free() to free it, and when the user transfers responsibility to libpng | |
| 2753 | for data that the user has allocated, the user must have used png_malloc() | |
| 2754 | or png_zalloc() to allocate it. | |
| 2755 | ||
| 2756 | If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword | |
| 2757 | separately, do not transfer responsibility for freeing text_ptr to libpng, | |
| 2758 | because when libpng fills a png_text structure it combines these members with | |
| 2759 | the key member, and png_free_data() will free only text_ptr.key. Similarly, | |
| 2760 | if you transfer responsibility for free'ing text_ptr from libpng to your | |
| 2761 | application, your application must not separately free those members. | |
| 2762 | For a more compact example of writing a PNG image, see the file example.c. | |
| 2763 | ||
| 2764 | .SH V. Modifying/Customizing libpng: | |
| 2765 | ||
| 2766 | There are two issues here. The first is changing how libpng does | |
| 2767 | standard things like memory allocation, input/output, and error handling. | |
| 2768 | The second deals with more complicated things like adding new chunks, | |
| 2769 | adding new transformations, and generally changing how libpng works. | |
| 2770 | Both of those are compile-time issues; that is, they are generally | |
| 2771 | determined at the time the code is written, and there is rarely a need | |
| 2772 | to provide the user with a means of changing them. | |
| 2773 | ||
| 2774 | Memory allocation, input/output, and error handling | |
| 2775 | ||
| 2776 | All of the memory allocation, input/output, and error handling in libpng | |
| 2777 | goes through callbacks that are user-settable. The default routines are | |
| 2778 | in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change | |
| 2779 | these functions, call the appropriate png_set_*_fn() function. | |
| 2780 | ||
| 2781 | Memory allocation is done through the functions png_malloc() | |
| 2782 | and png_free(). These currently just call the standard C functions. If | |
| 2783 | your pointers can't access more then 64K at a time, you will want to set | |
| 2784 | MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling | |
| 2785 | memory allocation on a platform will change between applications, these | |
| 2786 | functions must be modified in the library at compile time. If you prefer | |
| 2787 | to use a different method of allocating and freeing data, you can use | |
| 2788 | png_create_read_struct_2() or png_create_write_struct_2() to register | |
| 2789 | your own functions as described above. | |
| 2790 | These functions also provide a void pointer that can be retrieved via | |
| 2791 | ||
| 2792 | mem_ptr=png_get_mem_ptr(png_ptr); | |
| 2793 | ||
| 2794 | Your replacement memory functions must have prototypes as follows: | |
| 2795 | ||
| 2796 | png_voidp malloc_fn(png_structp png_ptr, | |
| 2797 | png_size_t size); | |
| 2798 | void free_fn(png_structp png_ptr, png_voidp ptr); | |
| 2799 | ||
| 2800 | Your malloc_fn() must return NULL in case of failure. The png_malloc() | |
| 2801 | function will normally call png_error() if it receives a NULL from the | |
| 2802 | system memory allocator or from your replacement malloc_fn(). | |
| 2803 | ||
| 2804 | Input/Output in libpng is done through png_read() and png_write(), | |
| 2805 | which currently just call fread() and fwrite(). The FILE * is stored in | |
| 2806 | png_struct and is initialized via png_init_io(). If you wish to change | |
| 2807 | the method of I/O, the library supplies callbacks that you can set | |
| 2808 | through the function png_set_read_fn() and png_set_write_fn() at run | |
| 2809 | time, instead of calling the png_init_io() function. These functions | |
| 2810 | also provide a void pointer that can be retrieved via the function | |
| 2811 | png_get_io_ptr(). For example: | |
| 2812 | ||
| 2813 | png_set_read_fn(png_structp read_ptr, | |
| 2814 | voidp read_io_ptr, png_rw_ptr read_data_fn) | |
| 2815 | ||
| 2816 | png_set_write_fn(png_structp write_ptr, | |
| 2817 | voidp write_io_ptr, png_rw_ptr write_data_fn, | |
| 2818 | png_flush_ptr output_flush_fn); | |
| 2819 | ||
| 2820 | voidp read_io_ptr = png_get_io_ptr(read_ptr); | |
| 2821 | voidp write_io_ptr = png_get_io_ptr(write_ptr); | |
| 2822 | ||
| 2823 | The replacement I/O functions must have prototypes as follows: | |
| 2824 | ||
| 2825 | void user_read_data(png_structp png_ptr, | |
| 2826 | png_bytep data, png_size_t length); | |
| 2827 | void user_write_data(png_structp png_ptr, | |
| 2828 | png_bytep data, png_size_t length); | |
| 2829 | void user_flush_data(png_structp png_ptr); | |
| 2830 | ||
| 2831 | Supplying NULL for the read, write, or flush functions sets them back | |
| 2832 | to using the default C stream functions. It is an error to read from | |
| 2833 | a write stream, and vice versa. | |
| 2834 | ||
| 2835 | Error handling in libpng is done through png_error() and png_warning(). | |
| 2836 | Errors handled through png_error() are fatal, meaning that png_error() | |
| 2837 | should never return to its caller. Currently, this is handled via | |
| 2838 | setjmp() and longjmp() (unless you have compiled libpng with | |
| 2839 | PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()), | |
| 2840 | but you could change this to do things like exit() if you should wish. | |
| 2841 | ||
| 2842 | On non-fatal errors, png_warning() is called | |
| 2843 | to print a warning message, and then control returns to the calling code. | |
| 2844 | By default png_error() and png_warning() print a message on stderr via | |
| 2845 | fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined | |
| 2846 | (because you don't want the messages) or PNG_NO_STDIO defined (because | |
| 2847 | fprintf() isn't available). If you wish to change the behavior of the error | |
| 2848 | functions, you will need to set up your own message callbacks. These | |
| 2849 | functions are normally supplied at the time that the png_struct is created. | |
| 2850 | It is also possible to redirect errors and warnings to your own replacement | |
| 2851 | functions after png_create_*_struct() has been called by calling: | |
| 2852 | ||
| 2853 | png_set_error_fn(png_structp png_ptr, | |
| 2854 | png_voidp error_ptr, png_error_ptr error_fn, | |
| 2855 | png_error_ptr warning_fn); | |
| 2856 | ||
| 2857 | png_voidp error_ptr = png_get_error_ptr(png_ptr); | |
| 2858 | ||
| 2859 | If NULL is supplied for either error_fn or warning_fn, then the libpng | |
| 2860 | default function will be used, calling fprintf() and/or longjmp() if a | |
| 2861 | problem is encountered. The replacement error functions should have | |
| 2862 | parameters as follows: | |
| 2863 | ||
| 2864 | void user_error_fn(png_structp png_ptr, | |
| 2865 | png_const_charp error_msg); | |
| 2866 | void user_warning_fn(png_structp png_ptr, | |
| 2867 | png_const_charp warning_msg); | |
| 2868 | ||
| 2869 | The motivation behind using setjmp() and longjmp() is the C++ throw and | |
| 2870 | catch exception handling methods. This makes the code much easier to write, | |
| 2871 | as there is no need to check every return code of every function call. | |
| 2872 | However, there are some uncertainties about the status of local variables | |
| 2873 | after a longjmp, so the user may want to be careful about doing anything after | |
| 2874 | setjmp returns non-zero besides returning itself. Consult your compiler | |
| 2875 | documentation for more details. For an alternative approach, you may wish | |
| 2876 | to use the "cexcept" facility (see http://cexcept.sourceforge.net). | |
| 2877 | ||
| 2878 | .SS Custom chunks | |
| 2879 | ||
| 2880 | If you need to read or write custom chunks, you may need to get deeper | |
| 2881 | into the libpng code. The library now has mechanisms for storing | |
| 2882 | and writing chunks of unknown type; you can even declare callbacks | |
| 2883 | for custom chunks. However, this may not be good enough if the | |
| 2884 | library code itself needs to know about interactions between your | |
| 2885 | chunk and existing `intrinsic' chunks. | |
| 2886 | ||
| 2887 | If you need to write a new intrinsic chunk, first read the PNG | |
| 2888 | specification. Acquire a first level of | |
| 2889 | understanding of how it works. Pay particular attention to the | |
| 2890 | sections that describe chunk names, and look at how other chunks were | |
| 2891 | designed, so you can do things similarly. Second, check out the | |
| 2892 | sections of libpng that read and write chunks. Try to find a chunk | |
| 2893 | that is similar to yours and use it as a template. More details can | |
| 2894 | be found in the comments inside the code. It is best to handle unknown | |
| 2895 | chunks in a generic method, via callback functions, instead of by | |
| 2896 | modifying libpng functions. | |
| 2897 | ||
| 2898 | If you wish to write your own transformation for the data, look through | |
| 2899 | the part of the code that does the transformations, and check out some of | |
| 2900 | the simpler ones to get an idea of how they work. Try to find a similar | |
| 2901 | transformation to the one you want to add and copy off of it. More details | |
| 2902 | can be found in the comments inside the code itself. | |
| 2903 | ||
| 2904 | .SS Configuring for 16 bit platforms | |
| 2905 | ||
| 2906 | You will want to look into zconf.h to tell zlib (and thus libpng) that | |
| 2907 | it cannot allocate more then 64K at a time. Even if you can, the memory | |
| 2908 | won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K. | |
| 2909 | ||
| 2910 | .SS Configuring for DOS | |
| 2911 | ||
| 2912 | For DOS users who only have access to the lower 640K, you will | |
| 2913 | have to limit zlib's memory usage via a png_set_compression_mem_level() | |
| 2914 | call. See zlib.h or zconf.h in the zlib library for more information. | |
| 2915 | ||
| 2916 | .SS Configuring for Medium Model | |
| 2917 | ||
| 2918 | Libpng's support for medium model has been tested on most of the popular | |
| 2919 | compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets | |
| 2920 | defined, and FAR gets defined to far in pngconf.h, and you should be | |
| 2921 | all set. Everything in the library (except for zlib's structure) is | |
| 2922 | expecting far data. You must use the typedefs with the p or pp on | |
| 2923 | the end for pointers (or at least look at them and be careful). Make | |
| 2924 | note that the rows of data are defined as png_bytepp, which is an | |
| 2925 | unsigned char far * far *. | |
| 2926 | ||
| 2927 | .SS Configuring for gui/windowing platforms: | |
| 2928 | ||
| 2929 | You will need to write new error and warning functions that use the GUI | |
| 2930 | interface, as described previously, and set them to be the error and | |
| 2931 | warning functions at the time that png_create_*_struct() is called, | |
| 2932 | in order to have them available during the structure initialization. | |
| 2933 | They can be changed later via png_set_error_fn(). On some compilers, | |
| 2934 | you may also have to change the memory allocators (png_malloc, etc.). | |
| 2935 | ||
| 2936 | .SS Configuring for compiler xxx: | |
| 2937 | ||
| 2938 | All includes for libpng are in pngconf.h. If you need to add/change/delete | |
| 2939 | an include, this is the place to do it. The includes that are not | |
| 2940 | needed outside libpng are protected by the PNG_INTERNAL definition, | |
| 2941 | which is only defined for those routines inside libpng itself. The | |
| 2942 | files in libpng proper only include png.h, which includes pngconf.h. | |
| 2943 | ||
| 2944 | .SS Configuring zlib: | |
| 2945 | ||
| 2946 | There are special functions to configure the compression. Perhaps the | |
| 2947 | most useful one changes the compression level, which currently uses | |
| 2948 | input compression values in the range 0 - 9. The library normally | |
| 2949 | uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests | |
| 2950 | have shown that for a large majority of images, compression values in | |
| 2951 | the range 3-6 compress nearly as well as higher levels, and do so much | |
| 2952 | faster. For online applications it may be desirable to have maximum speed | |
| 2953 | (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also | |
| 2954 | specify no compression (Z_NO_COMPRESSION = 0), but this would create | |
| 2955 | files larger than just storing the raw bitmap. You can specify the | |
| 2956 | compression level by calling: | |
| 2957 | ||
| 2958 | png_set_compression_level(png_ptr, level); | |
| 2959 | ||
| 2960 | Another useful one is to reduce the memory level used by the library. | |
| 2961 | The memory level defaults to 8, but it can be lowered if you are | |
| 2962 | short on memory (running DOS, for example, where you only have 640K). | |
| 2963 | Note that the memory level does have an effect on compression; among | |
| 2964 | other things, lower levels will result in sections of incompressible | |
| 2965 | data being emitted in smaller stored blocks, with a correspondingly | |
| 2966 | larger relative overhead of up to 15% in the worst case. | |
| 2967 | ||
| 2968 | png_set_compression_mem_level(png_ptr, level); | |
| 2969 | ||
| 2970 | The other functions are for configuring zlib. They are not recommended | |
| 2971 | for normal use and may result in writing an invalid PNG file. See | |
| 2972 | zlib.h for more information on what these mean. | |
| 2973 | ||
| 2974 | png_set_compression_strategy(png_ptr, | |
| 2975 | strategy); | |
| 2976 | png_set_compression_window_bits(png_ptr, | |
| 2977 | window_bits); | |
| 2978 | png_set_compression_method(png_ptr, method); | |
| 2979 | png_set_compression_buffer_size(png_ptr, size); | |
| 2980 | ||
| 2981 | .SS Controlling row filtering | |
| 2982 | ||
| 2983 | If you want to control whether libpng uses filtering or not, which | |
| 2984 | filters are used, and how it goes about picking row filters, you | |
| 2985 | can call one of these functions. The selection and configuration | |
| 2986 | of row filters can have a significant impact on the size and | |
| 2987 | encoding speed and a somewhat lesser impact on the decoding speed | |
| 2988 | of an image. Filtering is enabled by default for RGB and grayscale | |
| 2989 | images (with and without alpha), but not for paletted images nor | |
| 2990 | for any images with bit depths less than 8 bits/pixel. | |
| 2991 | ||
| 2992 | The 'method' parameter sets the main filtering method, which is | |
| 2993 | currently only '0' in the PNG 1.2 specification. The 'filters' | |
| 2994 | parameter sets which filter(s), if any, should be used for each | |
| 2995 | scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS | |
| 2996 | to turn filtering on and off, respectively. | |
| 2997 | ||
| 2998 | Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB, | |
| 2999 | PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise | |
| 3000 | ORed together with '|' to specify one or more filters to use. | |
| 3001 | These filters are described in more detail in the PNG specification. | |
| 3002 | If you intend to change the filter type during the course of writing | |
| 3003 | the image, you should start with flags set for all of the filters | |
| 3004 | you intend to use so that libpng can initialize its internal | |
| 3005 | structures appropriately for all of the filter types. (Note that this | |
| 3006 | means the first row must always be adaptively filtered, because libpng | |
| 3007 | currently does not allocate the filter buffers until png_write_row() | |
| 3008 | is called for the first time.) | |
| 3009 | ||
| 3010 | filters = PNG_FILTER_NONE | PNG_FILTER_SUB | |
| 3011 | PNG_FILTER_UP | PNG_FILTER_AVE | | |
| 3012 | PNG_FILTER_PAETH | PNG_ALL_FILTERS; | |
| 3013 | ||
| 3014 | png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, | |
| 3015 | filters); | |
| 3016 | The second parameter can also be | |
| 3017 | PNG_INTRAPIXEL_DIFFERENCING if you are | |
| 3018 | writing a PNG to be embedded in a MNG | |
| 3019 | datastream. This parameter must be the | |
| 3020 | same as the value of filter_method used | |
| 3021 | in png_set_IHDR(). | |
| 3022 | ||
| 3023 | It is also possible to influence how libpng chooses from among the | |
| 3024 | available filters. This is done in one or both of two ways - by | |
| 3025 | telling it how important it is to keep the same filter for successive | |
| 3026 | rows, and by telling it the relative computational costs of the filters. | |
| 3027 | ||
| 3028 | double weights[3] = {1.5, 1.3, 1.1}, | |
| 3029 | costs[PNG_FILTER_VALUE_LAST] = | |
| 3030 | {1.0, 1.3, 1.3, 1.5, 1.7}; | |
| 3031 | ||
| 3032 | png_set_filter_heuristics(png_ptr, | |
| 3033 | PNG_FILTER_HEURISTIC_WEIGHTED, 3, | |
| 3034 | weights, costs); | |
| 3035 | ||
| 3036 | The weights are multiplying factors that indicate to libpng that the | |
| 3037 | row filter should be the same for successive rows unless another row filter | |
| 3038 | is that many times better than the previous filter. In the above example, | |
| 3039 | if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a | |
| 3040 | "sum of absolute differences" 1.5 x 1.3 times higher than other filters | |
| 3041 | and still be chosen, while the NONE filter could have a sum 1.1 times | |
| 3042 | higher than other filters and still be chosen. Unspecified weights are | |
| 3043 | taken to be 1.0, and the specified weights should probably be declining | |
| 3044 | like those above in order to emphasize recent filters over older filters. | |
| 3045 | ||
| 3046 | The filter costs specify for each filter type a relative decoding cost | |
| 3047 | to be considered when selecting row filters. This means that filters | |
| 3048 | with higher costs are less likely to be chosen over filters with lower | |
| 3049 | costs, unless their "sum of absolute differences" is that much smaller. | |
| 3050 | The costs do not necessarily reflect the exact computational speeds of | |
| 3051 | the various filters, since this would unduly influence the final image | |
| 3052 | size. | |
| 3053 | ||
| 3054 | Note that the numbers above were invented purely for this example and | |
| 3055 | are given only to help explain the function usage. Little testing has | |
| 3056 | been done to find optimum values for either the costs or the weights. | |
| 3057 | ||
| 3058 | .SS Removing unwanted object code | |
| 3059 | ||
| 3060 | There are a bunch of #define's in pngconf.h that control what parts of | |
| 3061 | libpng are compiled. All the defines end in _SUPPORTED. If you are | |
| 3062 | never going to use a capability, you can change the #define to #undef | |
| 3063 | before recompiling libpng and save yourself code and data space, or | |
| 3064 | you can turn off individual capabilities with defines that begin with | |
| 3065 | PNG_NO_. | |
| 3066 | ||
| 3067 | You can also turn all of the transforms and ancillary chunk capabilities | |
| 3068 | off en masse with compiler directives that define | |
| 3069 | PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS, | |
| 3070 | or all four, | |
| 3071 | along with directives to turn on any of the capabilities that you do | |
| 3072 | want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable | |
| 3073 | the extra transformations but still leave the library fully capable of reading | |
| 3074 | and writing PNG files with all known public chunks | |
| 3075 | Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive | |
| 3076 | produces a library that is incapable of reading or writing ancillary chunks. | |
| 3077 | If you are not using the progressive reading capability, you can | |
| 3078 | turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse | |
| 3079 | this with the INTERLACING capability, which you'll still have). | |
| 3080 | ||
| 3081 | All the reading and writing specific code are in separate files, so the | |
| 3082 | linker should only grab the files it needs. However, if you want to | |
| 3083 | make sure, or if you are building a stand alone library, all the | |
| 3084 | reading files start with pngr and all the writing files start with | |
| 3085 | pngw. The files that don't match either (like png.c, pngtrans.c, etc.) | |
| 3086 | are used for both reading and writing, and always need to be included. | |
| 3087 | The progressive reader is in pngpread.c | |
| 3088 | ||
| 3089 | If you are creating or distributing a dynamically linked library (a .so | |
| 3090 | or DLL file), you should not remove or disable any parts of the library, | |
| 3091 | as this will cause applications linked with different versions of the | |
| 3092 | library to fail if they call functions not available in your library. | |
| 3093 | The size of the library itself should not be an issue, because only | |
| 3094 | those sections that are actually used will be loaded into memory. | |
| 3095 | ||
| 3096 | .SS Requesting debug printout | |
| 3097 | ||
| 3098 | The macro definition PNG_DEBUG can be used to request debugging | |
| 3099 | printout. Set it to an integer value in the range 0 to 3. Higher | |
| 3100 | numbers result in increasing amounts of debugging information. The | |
| 3101 | information is printed to the "stderr" file, unless another file | |
| 3102 | name is specified in the PNG_DEBUG_FILE macro definition. | |
| 3103 | ||
| 3104 | When PNG_DEBUG > 0, the following functions (macros) become available: | |
| 3105 | ||
| 3106 | png_debug(level, message) | |
| 3107 | png_debug1(level, message, p1) | |
| 3108 | png_debug2(level, message, p1, p2) | |
| 3109 | ||
| 3110 | in which "level" is compared to PNG_DEBUG to decide whether to print | |
| 3111 | the message, "message" is the formatted string to be printed, | |
| 3112 | and p1 and p2 are parameters that are to be embedded in the string | |
| 3113 | according to printf-style formatting directives. For example, | |
| 3114 | ||
| 3115 | png_debug1(2, "foo=%d\n", foo); | |
| 3116 | ||
| 3117 | is expanded to | |
| 3118 | ||
| 3119 | if(PNG_DEBUG > 2) | |
| 3120 | fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo); | |
| 3121 | ||
| 3122 | When PNG_DEBUG is defined but is zero, the macros aren't defined, but you | |
| 3123 | can still use PNG_DEBUG to control your own debugging: | |
| 3124 | ||
| 3125 | #ifdef PNG_DEBUG | |
| 3126 | fprintf(stderr, ... | |
| 3127 | #endif | |
| 3128 | ||
| 3129 | When PNG_DEBUG = 1, the macros are defined, but only png_debug statements | |
| 3130 | having level = 0 will be printed. There aren't any such statements in | |
| 3131 | this version of libpng, but if you insert some they will be printed. | |
| 3132 | ||
| 3133 | .SH VII. MNG support | |
| 3134 | ||
| 3135 | The MNG specification (available at http://www.libpng.org/pub/mng) allows | |
| 3136 | certain extensions to PNG for PNG images that are embedded in MNG datastreams. | |
| 3137 | Libpng can support some of these extensions. To enable them, use the | |
| 3138 | png_permit_mng_features() function: | |
| 3139 | ||
| 3140 | feature_set = png_permit_mng_features(png_ptr, mask) | |
| 3141 | mask is a png_uint_32 containing the bitwise OR of the | |
| 3142 | features you want to enable. These include | |
| 3143 | PNG_FLAG_MNG_EMPTY_PLTE | |
| 3144 | PNG_FLAG_MNG_FILTER_64 | |
| 3145 | PNG_ALL_MNG_FEATURES | |
| 3146 | feature_set is a png_uint_32 that is the bitwise AND of | |
| 3147 | your mask with the set of MNG features that is | |
| 3148 | supported by the version of libpng that you are using. | |
| 3149 | ||
| 3150 | It is an error to use this function when reading or writing a standalone | |
| 3151 | PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped | |
| 3152 | in a MNG datastream. As a minimum, it must have the MNG 8-byte signature | |
| 3153 | and the MHDR and MEND chunks. Libpng does not provide support for these | |
| 3154 | or any other MNG chunks; your application must provide its own support for | |
| 3155 | them. You may wish to consider using libmng (available at | |
| 3156 | http://www.libmng.com) instead. | |
| 3157 | ||
| 3158 | .SH VIII. Changes to Libpng from version 0.88 | |
| 3159 | ||
| 3160 | It should be noted that versions of libpng later than 0.96 are not | |
| 3161 | distributed by the original libpng author, Guy Schalnat, nor by | |
| 3162 | Andreas Dilger, who had taken over from Guy during 1996 and 1997, and | |
| 3163 | distributed versions 0.89 through 0.96, but rather by another member | |
| 3164 | of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are | |
| 3165 | still alive and well, but they have moved on to other things. | |
| 3166 | ||
| 3167 | The old libpng functions png_read_init(), png_write_init(), | |
| 3168 | png_info_init(), png_read_destroy(), and png_write_destroy() have been | |
| 3169 | moved to PNG_INTERNAL in version 0.95 to discourage their use. These | |
| 3170 | functions will be removed from libpng version 2.0.0. | |
| 3171 | ||
| 3172 | The preferred method of creating and initializing the libpng structures is | |
| 3173 | via the png_create_read_struct(), png_create_write_struct(), and | |
| 3174 | png_create_info_struct() because they isolate the size of the structures | |
| 3175 | from the application, allow version error checking, and also allow the | |
| 3176 | use of custom error handling routines during the initialization, which | |
| 3177 | the old functions do not. The functions png_read_destroy() and | |
| 3178 | png_write_destroy() do not actually free the memory that libpng | |
| 3179 | allocated for these structs, but just reset the data structures, so they | |
| 3180 | can be used instead of png_destroy_read_struct() and | |
| 3181 | png_destroy_write_struct() if you feel there is too much system overhead | |
| 3182 | allocating and freeing the png_struct for each image read. | |
| 3183 | ||
| 3184 | Setting the error callbacks via png_set_message_fn() before | |
| 3185 | png_read_init() as was suggested in libpng-0.88 is no longer supported | |
| 3186 | because this caused applications that do not use custom error functions | |
| 3187 | to fail if the png_ptr was not initialized to zero. It is still possible | |
| 3188 | to set the error callbacks AFTER png_read_init(), or to change them with | |
| 3189 | png_set_error_fn(), which is essentially the same function, but with a new | |
| 3190 | name to force compilation errors with applications that try to use the old | |
| 3191 | method. | |
| 3192 | ||
| 3193 | Starting with version 1.0.7, you can find out which version of the library | |
| 3194 | you are using at run-time: | |
| 3195 | ||
| 3196 | png_uint_32 libpng_vn = png_access_version_number(); | |
| 3197 | ||
| 3198 | The number libpng_vn is constructed from the major version, minor | |
| 3199 | version with leading zero, and release number with leading zero, | |
| 3200 | (e.g., libpng_vn for version 1.0.7 is 10007). | |
| 3201 | ||
| 3202 | You can also check which version of png.h you used when compiling your | |
| 3203 | application: | |
| 3204 | ||
| 3205 | png_uint_32 application_vn = PNG_LIBPNG_VER; | |
| 3206 | ||
| 3207 | .SH IX. Y2K Compliance in libpng | |
| 3208 | ||
| 3209 | September 8, 2007 | |
| 3210 | ||
| 3211 | Since the PNG Development group is an ad-hoc body, we can't make | |
| 3212 | an official declaration. | |
| 3213 | ||
| 3214 | This is your unofficial assurance that libpng from version 0.71 and | |
| 3215 | upward through 1.2.20 are Y2K compliant. It is my belief that earlier | |
| 3216 | versions were also Y2K compliant. | |
| 3217 | ||
| 3218 | Libpng only has three year fields. One is a 2-byte unsigned integer that | |
| 3219 | will hold years up to 65535. The other two hold the date in text | |
| 3220 | format, and will hold years up to 9999. | |
| 3221 | ||
| 3222 | The integer is | |
| 3223 | "png_uint_16 year" in png_time_struct. | |
| 3224 | ||
| 3225 | The strings are | |
| 3226 | "png_charp time_buffer" in png_struct and | |
| 3227 | "near_time_buffer", which is a local character string in png.c. | |
| 3228 | ||
| 3229 | There are seven time-related functions: | |
| 3230 | ||
| 3231 | png_convert_to_rfc_1123() in png.c | |
| 3232 | (formerly png_convert_to_rfc_1152() in error) | |
| 3233 | png_convert_from_struct_tm() in pngwrite.c, called | |
| 3234 | in pngwrite.c | |
| 3235 | png_convert_from_time_t() in pngwrite.c | |
| 3236 | png_get_tIME() in pngget.c | |
| 3237 | png_handle_tIME() in pngrutil.c, called in pngread.c | |
| 3238 | png_set_tIME() in pngset.c | |
| 3239 | png_write_tIME() in pngwutil.c, called in pngwrite.c | |
| 3240 | ||
| 3241 | All appear to handle dates properly in a Y2K environment. The | |
| 3242 | png_convert_from_time_t() function calls gmtime() to convert from system | |
| 3243 | clock time, which returns (year - 1900), which we properly convert to | |
| 3244 | the full 4-digit year. There is a possibility that applications using | |
| 3245 | libpng are not passing 4-digit years into the png_convert_to_rfc_1123() | |
| 3246 | function, or that they are incorrectly passing only a 2-digit year | |
| 3247 | instead of "year - 1900" into the png_convert_from_struct_tm() function, | |
| 3248 | but this is not under our control. The libpng documentation has always | |
| 3249 | stated that it works with 4-digit years, and the APIs have been | |
| 3250 | documented as such. | |
| 3251 | ||
| 3252 | The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned | |
| 3253 | integer to hold the year, and can hold years as large as 65535. | |
| 3254 | ||
| 3255 | zlib, upon which libpng depends, is also Y2K compliant. It contains | |
| 3256 | no date-related code. | |
| 3257 | ||
| 3258 | ||
| 3259 | Glenn Randers-Pehrson | |
| 3260 | libpng maintainer | |
| 3261 | PNG Development Group | |
| 3262 | ||
| 3263 | .SH NOTE | |
| 3264 | ||
| 3265 | Note about libpng version numbers: | |
| 3266 | ||
| 3267 | Due to various miscommunications, unforeseen code incompatibilities | |
| 3268 | and occasional factors outside the authors' control, version numbering | |
| 3269 | on the library has not always been consistent and straightforward. | |
| 3270 | The following table summarizes matters since version 0.89c, which was | |
| 3271 | the first widely used release: | |
| 3272 | ||
| 3273 | source png.h png.h shared-lib | |
| 3274 | version string int version | |
| 3275 | ------- ------ ----- ---------- | |
| 3276 | 0.89c ("beta 3") 0.89 89 1.0.89 | |
| 3277 | 0.90 ("beta 4") 0.90 90 0.90 | |
| 3278 | 0.95 ("beta 5") 0.95 95 0.95 | |
| 3279 | 0.96 ("beta 6") 0.96 96 0.96 | |
| 3280 | 0.97b ("beta 7") 1.00.97 97 1.0.1 | |
| 3281 | 0.97c 0.97 97 2.0.97 | |
| 3282 | 0.98 0.98 98 2.0.98 | |
| 3283 | 0.99 0.99 98 2.0.99 | |
| 3284 | 0.99a-m 0.99 99 2.0.99 | |
| 3285 | 1.00 1.00 100 2.1.0 | |
| 3286 | 1.0.0 1.0.0 100 2.1.0 | |
| 3287 | 1.0.0 (from here on, the 100 2.1.0 | |
| 3288 | 1.0.1 png.h string is 10001 2.1.0 | |
| 3289 | 1.0.1a-e identical to the 10002 from here on, the | |
| 3290 | 1.0.2 source version) 10002 shared library is 2.V | |
| 3291 | 1.0.2a-b 10003 where V is the source | |
| 3292 | 1.0.1 10001 code version except as | |
| 3293 | 1.0.1a-e 10002 2.1.0.1a-e noted. | |
| 3294 | 1.0.2 10002 2.1.0.2 | |
| 3295 | 1.0.2a-b 10003 2.1.0.2a-b | |
| 3296 | 1.0.3 10003 2.1.0.3 | |
| 3297 | 1.0.3a-d 10004 2.1.0.3a-d | |
| 3298 | 1.0.4 10004 2.1.0.4 | |
| 3299 | 1.0.4a-f 10005 2.1.0.4a-f | |
| 3300 | 1.0.5 (+ 2 patches) 10005 2.1.0.5 | |
| 3301 | 1.0.5a-d 10006 2.1.0.5a-d | |
| 3302 | 1.0.5e-r 10100 2.1.0.5e-r | |
| 3303 | 1.0.5s-v 10006 2.1.0.5s-v | |
| 3304 | 1.0.6 (+ 3 patches) 10006 2.1.0.6 | |
| 3305 | 1.0.6d-g 10007 2.1.0.6d-g | |
| 3306 | 1.0.6h 10007 10.6h | |
| 3307 | 1.0.6i 10007 10.6i | |
| 3308 | 1.0.6j 10007 2.1.0.6j | |
| 3309 | 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14 | |
| 3310 | 1.0.7beta15-18 1 10007 2.1.0.7beta15-18 | |
| 3311 | 1.0.7rc1-2 1 10007 2.1.0.7rc1-2 | |
| 3312 | 1.0.7 1 10007 2.1.0.7 | |
| 3313 | 1.0.8beta1-4 1 10008 2.1.0.8beta1-4 | |
| 3314 | 1.0.8rc1 1 10008 2.1.0.8rc1 | |
| 3315 | 1.0.8 1 10008 2.1.0.8 | |
| 3316 | 1.0.9beta1-6 1 10009 2.1.0.9beta1-6 | |
| 3317 | 1.0.9rc1 1 10009 2.1.0.9rc1 | |
| 3318 | 1.0.9beta7-10 1 10009 2.1.0.9beta7-10 | |
| 3319 | 1.0.9rc2 1 10009 2.1.0.9rc2 | |
| 3320 | 1.0.9 1 10009 2.1.0.9 | |
| 3321 | 1.0.10beta1 1 10010 2.1.0.10beta1 | |
| 3322 | 1.0.10rc1 1 10010 2.1.0.10rc1 | |
| 3323 | 1.0.10 1 10010 2.1.0.10 | |
| 3324 | 1.0.11beta1-3 1 10011 2.1.0.11beta1-3 | |
| 3325 | 1.0.11rc1 1 10011 2.1.0.11rc1 | |
| 3326 | 1.0.11 1 10011 2.1.0.11 | |
| 3327 | 1.0.12beta1-2 2 10012 2.1.0.12beta1-2 | |
| 3328 | 1.0.12rc1 2 10012 2.1.0.12rc1 | |
| 3329 | 1.0.12 2 10012 2.1.0.12 | |
| 3330 | 1.1.0a-f - 10100 2.1.1.0a-f abandoned | |
| 3331 | 1.2.0beta1-2 2 10200 2.1.2.0beta1-2 | |
| 3332 | 1.2.0beta3-5 3 10200 3.1.2.0beta3-5 | |
| 3333 | 1.2.0rc1 3 10200 3.1.2.0rc1 | |
| 3334 | 1.2.0 3 10200 3.1.2.0 | |
| 3335 | 1.2.1beta-4 3 10201 3.1.2.1beta1-4 | |
| 3336 | 1.2.1rc1-2 3 10201 3.1.2.1rc1-2 | |
| 3337 | 1.2.1 3 10201 3.1.2.1 | |
| 3338 | 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6 | |
| 3339 | 1.0.13beta1 10 10013 10.so.0.1.0.13beta1 | |
| 3340 | 1.0.13rc1 10 10013 10.so.0.1.0.13rc1 | |
| 3341 | 1.2.2rc1 12 10202 12.so.0.1.2.2rc1 | |
| 3342 | 1.0.13 10 10013 10.so.0.1.0.13 | |
| 3343 | 1.2.2 12 10202 12.so.0.1.2.2 | |
| 3344 | 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6 | |
| 3345 | 1.2.3 12 10203 12.so.0.1.2.3 | |
| 3346 | 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3 | |
| 3347 | 1.2.4rc1 13 10204 12.so.0.1.2.4rc1 | |
| 3348 | 1.0.14 10 10014 10.so.0.1.0.14 | |
| 3349 | 1.2.4 13 10204 12.so.0.1.2.4 | |
| 3350 | 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2 | |
| 3351 | 1.0.15rc1 10 10015 10.so.0.1.0.15rc1 | |
| 3352 | 1.0.15 10 10015 10.so.0.1.0.15 | |
| 3353 | 1.2.5 13 10205 12.so.0.1.2.5 | |
| 3354 | 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4 | |
| 3355 | 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5 | |
| 3356 | 1.0.16 10 10016 10.so.0.1.0.16 | |
| 3357 | 1.2.6 13 10206 12.so.0.1.2.6 | |
| 3358 | 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2 | |
| 3359 | 1.0.17rc1 10 10017 10.so.0.1.0.17rc1 | |
| 3360 | 1.2.7rc1 13 10207 12.so.0.1.2.7rc1 | |
| 3361 | 1.0.17 10 10017 10.so.0.1.0.17 | |
| 3362 | 1.2.7 13 10207 12.so.0.1.2.7 | |
| 3363 | 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5 | |
| 3364 | 1.0.18rc1-5 10 10018 10.so.0.1.0.18rc1-5 | |
| 3365 | 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5 | |
| 3366 | 1.0.18 10 10018 10.so.0.1.0.18 | |
| 3367 | 1.2.8 13 10208 12.so.0.1.2.8 | |
| 3368 | 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3 | |
| 3369 | 1.2.9beta4-11 13 10209 12.so.0.9[.0] | |
| 3370 | 1.2.9rc1 13 10209 12.so.0.9[.0] | |
| 3371 | 1.2.9 13 10209 12.so.0.9[.0] | |
| 3372 | 1.2.10beta1-8 13 10210 12.so.0.10[.0] | |
| 3373 | 1.2.10rc1-3 13 10210 12.so.0.10[.0] | |
| 3374 | 1.2.10 13 10210 12.so.0.10[.0] | |
| 3375 | 1.2.11beta1-4 13 10211 12.so.0.11[.0] | |
| 3376 | 1.0.19rc1-5 10 10019 10.so.0.19[.0] | |
| 3377 | 1.2.11rc1-5 13 10211 12.so.0.11[.0] | |
| 3378 | 1.0.19 10 10019 10.so.0.19[.0] | |
| 3379 | 1.2.11 13 10211 12.so.0.11[.0] | |
| 3380 | 1.0.20 10 10020 10.so.0.20[.0] | |
| 3381 | 1.2.12 13 10212 12.so.0.12[.0] | |
| 3382 | 1.2.13beta1 13 10213 12.so.0.13[.0] | |
| 3383 | 1.0.21 10 10021 10.so.0.21[.0] | |
| 3384 | 1.2.13 13 10213 12.so.0.13[.0] | |
| 3385 | 1.2.14beta1-2 13 10214 12.so.0.14[.0] | |
| 3386 | 1.0.22rc1 10 10022 10.so.0.22[.0] | |
| 3387 | 1.2.14rc1 13 10214 12.so.0.14[.0] | |
| 3388 | 1.2.15beta1-6 13 10215 12.so.0.15[.0] | |
| 3389 | 1.0.23rc1-5 10 10023 10.so.0.23[.0] | |
| 3390 | 1.2.15rc1-5 13 10215 12.so.0.15[.0] | |
| 3391 | 1.0.23 10 10023 10.so.0.23[.0] | |
| 3392 | 1.2.15 13 10215 12.so.0.15[.0] | |
| 3393 | 1.2.16beta1-2 13 10216 12.so.0.16[.0] | |
| 3394 | 1.2.16rc1 13 10216 12.so.0.16[.0] | |
| 3395 | 1.0.24 10 10024 10.so.0.24[.0] | |
| 3396 | 1.2.16 13 10216 12.so.0.16[.0] | |
| 3397 | 1.2.17beta1-2 13 10217 12.so.0.17[.0] | |
| 3398 | 1.0.25rc1 10 10025 10.so.0.25[.0] | |
| 3399 | 1.2.17rc1-3 13 10217 12.so.0.17[.0] | |
| 3400 | 1.0.25 10 10025 10.so.0.25[.0] | |
| 3401 | 1.2.17 13 10217 12.so.0.17[.0] | |
| 3402 | 1.0.26 10 10026 10.so.0.26[.0] | |
| 3403 | 1.2.18 13 10218 12.so.0.18[.0] | |
| 3404 | 1.2.19beta1-31 13 10219 12.so.0.19[.0] | |
| 3405 | 1.0.27rc1-6 10 10027 10.so.0.27[.0] | |
| 3406 | 1.2.19rc1-6 13 10219 12.so.0.19[.0] | |
| 3407 | 1.0.27 10 10027 10.so.0.27[.0] | |
| 3408 | 1.2.19 13 10219 12.so.0.19[.0] | |
| 3409 | 1.2.20beta01-04 13 10220 12.so.0.20[.0] | |
| 3410 | 1.0.28rc1-6 10 10028 10.so.0.28[.0] | |
| 3411 | 1.2.20rc1-6 13 10220 12.so.0.20[.0] | |
| 3412 | 1.0.28 10 10028 10.so.0.28[.0] | |
| 3413 | 1.2.20 13 10220 12.so.0.20[.0] | |
| 3414 | ||
| 3415 | Henceforth the source version will match the shared-library minor | |
| 3416 | and patch numbers; the shared-library major version number will be | |
| 3417 | used for changes in backward compatibility, as it is intended. The | |
| 3418 | PNG_PNGLIB_VER macro, which is not used within libpng but is available | |
| 3419 | for applications, is an unsigned integer of the form xyyzz corresponding | |
| 3420 | to the source version x.y.z (leading zeros in y and z). Beta versions | |
| 3421 | were given the previous public release number plus a letter, until | |
| 3422 | version 1.0.6j; from then on they were given the upcoming public | |
| 3423 | release number plus "betaNN" or "rcN". | |
| 3424 | ||
| 3425 | .SH "SEE ALSO" | |
| 3426 | .IR libpngpf(3) ", " png(5) | |
| 3427 | .LP | |
| 3428 | .IR libpng : | |
| 3429 | .IP | |
| 3430 | http://libpng.sourceforge.net (follow the [DOWNLOAD] link) | |
| 3431 | http://www.libpng.org/pub/png | |
| 3432 | ||
| 3433 | .LP | |
| 3434 | .IR zlib : | |
| 3435 | .IP | |
| 3436 | (generally) at the same location as | |
| 3437 | .I libpng | |
| 3438 | or at | |
| 3439 | .br | |
| 3440 | ftp://ftp.info-zip.org/pub/infozip/zlib | |
| 3441 | ||
| 3442 | .LP | |
| 3443 | .IR PNG specification: RFC 2083 | |
| 3444 | .IP | |
| 3445 | (generally) at the same location as | |
| 3446 | .I libpng | |
| 3447 | or at | |
| 3448 | .br | |
| 3449 | ftp://ds.internic.net/rfc/rfc2083.txt | |
| 3450 | .br | |
| 3451 | or (as a W3C Recommendation) at | |
| 3452 | .br | |
| 3453 | http://www.w3.org/TR/REC-png.html | |
| 3454 | ||
| 3455 | .LP | |
| 3456 | In the case of any inconsistency between the PNG specification | |
| 3457 | and this library, the specification takes precedence. | |
| 3458 | ||
| 3459 | .SH AUTHORS | |
| 3460 | This man page: Glenn Randers-Pehrson | |
| 3461 | <glennrp at users.sourceforge.net> | |
| 3462 | ||
| 3463 | The contributing authors would like to thank all those who helped | |
| 3464 | with testing, bug fixes, and patience. This wouldn't have been | |
| 3465 | possible without all of you. | |
| 3466 | ||
| 3467 | Thanks to Frank J. T. Wojcik for helping with the documentation. | |
| 3468 | ||
| 3469 | Libpng version 1.2.20 - September 8, 2007: | |
| 3470 | Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc. | |
| 3471 | Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net). | |
| 3472 | ||
| 3473 | Supported by the PNG development group | |
| 3474 | .br | |
| 3475 | png-mng-implement at lists.sf.net | |
| 3476 | (subscription required; visit | |
| 3477 | png-mng-implement at lists.sourceforge.net (subscription required; visit | |
| 3478 | https://lists.sourceforge.net/lists/listinfo/png-mng-implement | |
| 3479 | to subscribe). | |
| 3480 | ||
| 3481 | .SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE: | |
| 3482 | ||
| 3483 | (This copy of the libpng notices is provided for your convenience. In case of | |
| 3484 | any discrepancy between this copy and the notices in the file png.h that is | |
| 3485 | included in the libpng distribution, the latter shall prevail.) | |
| 3486 | ||
| 3487 | If you modify libpng you may insert additional notices immediately following | |
| 3488 | this sentence. | |
| 3489 | ||
| 3490 | libpng versions 1.2.6, August 15, 2004, through 1.2.20, September 8, 2007, are | |
| 3491 | Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are | |
| 3492 | distributed according to the same disclaimer and license as libpng-1.2.5 | |
| 3493 | with the following individual added to the list of Contributing Authors | |
| 3494 | ||
| 3495 | Cosmin Truta | |
| 3496 | ||
| 3497 | libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are | |
| 3498 | Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are | |
| 3499 | distributed according to the same disclaimer and license as libpng-1.0.6 | |
| 3500 | with the following individuals added to the list of Contributing Authors | |
| 3501 | ||
| 3502 | Simon-Pierre Cadieux | |
| 3503 | Eric S. Raymond | |
| 3504 | Gilles Vollant | |
| 3505 | ||
| 3506 | and with the following additions to the disclaimer: | |
| 3507 | ||
| 3508 | There is no warranty against interference with your | |
| 3509 | enjoyment of the library or against infringement. | |
| 3510 | There is no warranty that our efforts or the library | |
| 3511 | will fulfill any of your particular purposes or needs. | |
| 3512 | This library is provided with all faults, and the entire | |
| 3513 | risk of satisfactory quality, performance, accuracy, and | |
| 3514 | effort is with the user. | |
| 3515 | ||
| 3516 | libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are | |
| 3517 | Copyright (c) 1998, 1999 Glenn Randers-Pehrson | |
| 3518 | Distributed according to the same disclaimer and license as libpng-0.96, | |
| 3519 | with the following individuals added to the list of Contributing Authors: | |
| 3520 | ||
| 3521 | Tom Lane | |
| 3522 | Glenn Randers-Pehrson | |
| 3523 | Willem van Schaik | |
| 3524 | ||
| 3525 | libpng versions 0.89, June 1996, through 0.96, May 1997, are | |
| 3526 | Copyright (c) 1996, 1997 Andreas Dilger | |
| 3527 | Distributed according to the same disclaimer and license as libpng-0.88, | |
| 3528 | with the following individuals added to the list of Contributing Authors: | |
| 3529 | ||
| 3530 | John Bowler | |
| 3531 | Kevin Bracey | |
| 3532 | Sam Bushell | |
| 3533 | Magnus Holmgren | |
| 3534 | Greg Roelofs | |
| 3535 | Tom Tanner | |
| 3536 | ||
| 3537 | libpng versions 0.5, May 1995, through 0.88, January 1996, are | |
| 3538 | Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc. | |
| 3539 | ||
| 3540 | For the purposes of this copyright and license, "Contributing Authors" | |
| 3541 | is defined as the following set of individuals: | |
| 3542 | ||
| 3543 | Andreas Dilger | |
| 3544 | Dave Martindale | |
| 3545 | Guy Eric Schalnat | |
| 3546 | Paul Schmidt | |
| 3547 | Tim Wegner | |
| 3548 | ||
| 3549 | The PNG Reference Library is supplied "AS IS". The Contributing Authors | |
| 3550 | and Group 42, Inc. disclaim all warranties, expressed or implied, | |
| 3551 | including, without limitation, the warranties of merchantability and of | |
| 3552 | fitness for any purpose. The Contributing Authors and Group 42, Inc. | |
| 3553 | assume no liability for direct, indirect, incidental, special, exemplary, | |
| 3554 | or consequential damages, which may result from the use of the PNG | |
| 3555 | Reference Library, even if advised of the possibility of such damage. | |
| 3556 | ||
| 3557 | Permission is hereby granted to use, copy, modify, and distribute this | |
| 3558 | source code, or portions hereof, for any purpose, without fee, subject | |
| 3559 | to the following restrictions: | |
| 3560 | ||
| 3561 | 1. The origin of this source code must not be misrepresented. | |
| 3562 | ||
| 3563 | 2. Altered versions must be plainly marked as such and | |
| 3564 | must not be misrepresented as being the original source. | |
| 3565 | ||
| 3566 | 3. This Copyright notice may not be removed or altered from | |
| 3567 | any source or altered source distribution. | |
| 3568 | ||
| 3569 | The Contributing Authors and Group 42, Inc. specifically permit, without | |
| 3570 | fee, and encourage the use of this source code as a component to | |
| 3571 | supporting the PNG file format in commercial products. If you use this | |
| 3572 | source code in a product, acknowledgment is not required but would be | |
| 3573 | appreciated. | |
| 3574 | ||
| 3575 | ||
| 3576 | A "png_get_copyright" function is available, for convenient use in "about" | |
| 3577 | boxes and the like: | |
| 3578 | ||
| 3579 | printf("%s",png_get_copyright(NULL)); | |
| 3580 | ||
| 3581 | Also, the PNG logo (in PNG format, of course) is supplied in the | |
| 3582 | files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31). | |
| 3583 | ||
| 3584 | Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a | |
| 3585 | certification mark of the Open Source Initiative. | |
| 3586 | ||
| 3587 | Glenn Randers-Pehrson | |
| 3588 | glennrp at users.sourceforge.net | |
| 3589 | September 8, 2007 | |
| 3590 | ||
| 3591 | .\" end of man page | |
| 3592 |