annotate mupdf-source/thirdparty/libjpeg/example.c @ 2:b50eed0cc0ef upstream

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author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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1 /*
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2 * example.c
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3 *
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4 * This file illustrates how to use the IJG code as a subroutine library
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5 * to read or write JPEG image files. You should look at this code in
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6 * conjunction with the documentation file libjpeg.txt.
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7 *
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8 * This code will not do anything useful as-is, but it may be helpful as a
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9 * skeleton for constructing routines that call the JPEG library.
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10 *
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11 * We present these routines in the same coding style used in the JPEG code
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12 * (ANSI function definitions, etc); but you are of course free to code your
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13 * routines in a different style if you prefer.
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14 */
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16 #include <stdio.h>
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18 /*
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19 * Include file for users of JPEG library.
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20 * You will need to have included system headers that define at least
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21 * the typedefs FILE and size_t before you can include jpeglib.h.
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22 * (stdio.h is sufficient on ANSI-conforming systems.)
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23 * You may also wish to include "jerror.h".
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24 */
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26 #include "jpeglib.h"
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28 /*
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29 * <setjmp.h> is used for the optional error recovery mechanism shown in
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30 * the second part of the example.
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31 */
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33 #include <setjmp.h>
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37 /******************** JPEG COMPRESSION SAMPLE INTERFACE *******************/
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39 /* This half of the example shows how to feed data into the JPEG compressor.
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40 * We present a minimal version that does not worry about refinements such
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41 * as error recovery (the JPEG code will just exit() if it gets an error).
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42 */
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45 /*
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46 * IMAGE DATA FORMATS:
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47 *
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48 * The standard input image format is a rectangular array of pixels, with
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49 * each pixel having the same number of "component" values (color channels).
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50 * Each pixel row is an array of JSAMPLEs (which typically are unsigned chars).
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51 * If you are working with color data, then the color values for each pixel
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52 * must be adjacent in the row; for example, R,G,B,R,G,B,R,G,B,... for 24-bit
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53 * RGB color.
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54 *
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55 * For this example, we'll assume that this data structure matches the way
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56 * our application has stored the image in memory, so we can just pass a
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57 * pointer to our image buffer. In particular, let's say that the image is
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58 * RGB color and is described by:
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59 */
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61 extern JSAMPLE * image_buffer; /* Points to large array of R,G,B-order data */
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62 extern int image_height; /* Number of rows in image */
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63 extern int image_width; /* Number of columns in image */
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66 /*
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67 * Sample routine for JPEG compression. We assume that the target file name
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68 * and a compression quality factor are passed in.
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69 */
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71 GLOBAL(void)
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72 write_JPEG_file (char * filename, int quality)
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73 {
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74 /* This struct contains the JPEG compression parameters and pointers to
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75 * working space (which is allocated as needed by the JPEG library).
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76 * It is possible to have several such structures, representing multiple
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77 * compression/decompression processes, in existence at once. We refer
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78 * to any one struct (and its associated working data) as a "JPEG object".
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79 */
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80 struct jpeg_compress_struct cinfo;
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81 /* This struct represents a JPEG error handler. It is declared separately
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82 * because applications often want to supply a specialized error handler
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83 * (see the second half of this file for an example). But here we just
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84 * take the easy way out and use the standard error handler, which will
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85 * print a message on stderr and call exit() if compression fails.
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86 * Note that this struct must live as long as the main JPEG parameter
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87 * struct, to avoid dangling-pointer problems.
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88 */
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89 struct jpeg_error_mgr jerr;
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90 /* More stuff */
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91 FILE * outfile; /* target file */
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92 JSAMPROW row_pointer[1]; /* pointer to JSAMPLE row[s] */
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93 int row_stride; /* physical row width in image buffer */
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95 /* Step 1: allocate and initialize JPEG compression object */
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97 /* We have to set up the error handler first, in case the initialization
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98 * step fails. (Unlikely, but it could happen if you are out of memory.)
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99 * This routine fills in the contents of struct jerr, and returns jerr's
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100 * address which we place into the link field in cinfo.
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101 */
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102 cinfo.err = jpeg_std_error(&jerr);
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103 /* Now we can initialize the JPEG compression object. */
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104 jpeg_create_compress(&cinfo);
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105
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106 /* Step 2: specify data destination (eg, a file) */
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107 /* Note: steps 2 and 3 can be done in either order. */
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108
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109 /* Here we use the library-supplied code to send compressed data to a
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110 * stdio stream. You can also write your own code to do something else.
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111 * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
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112 * requires it in order to write binary files.
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113 */
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114 if ((outfile = fopen(filename, "wb")) == NULL) {
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115 fprintf(stderr, "can't open %s\n", filename);
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116 exit(1);
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117 }
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118 jpeg_stdio_dest(&cinfo, outfile);
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119
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120 /* Step 3: set parameters for compression */
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121
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122 /* First we supply a description of the input image.
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123 * Four fields of the cinfo struct must be filled in:
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124 */
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125 cinfo.image_width = image_width; /* image width and height, in pixels */
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126 cinfo.image_height = image_height;
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127 cinfo.input_components = 3; /* # of color components per pixel */
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128 cinfo.in_color_space = JCS_RGB; /* colorspace of input image */
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129 /* Now use the library's routine to set default compression parameters.
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130 * (You must set at least cinfo.in_color_space before calling this,
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131 * since the defaults depend on the source color space.)
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132 */
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133 jpeg_set_defaults(&cinfo);
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134 /* Now you can set any non-default parameters you wish to.
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135 * Here we just illustrate the use of quality (quantization table) scaling:
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136 */
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137 jpeg_set_quality(&cinfo, quality, TRUE /* limit to baseline-JPEG values */);
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138
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139 /* Step 4: Start compressor */
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140
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141 /* TRUE ensures that we will write a complete interchange-JPEG file.
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142 * Pass TRUE unless you are very sure of what you're doing.
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143 */
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144 jpeg_start_compress(&cinfo, TRUE);
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145
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146 /* Step 5: while (scan lines remain to be written) */
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147 /* jpeg_write_scanlines(...); */
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148
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149 /* Here we use the library's state variable cinfo.next_scanline as the
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150 * loop counter, so that we don't have to keep track ourselves.
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151 * To keep things simple, we pass one scanline per call; you can pass
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152 * more if you wish, though.
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153 */
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154 row_stride = image_width * 3; /* JSAMPLEs per row in image_buffer */
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155
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156 while (cinfo.next_scanline < cinfo.image_height) {
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157 /* jpeg_write_scanlines expects an array of pointers to scanlines.
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158 * Here the array is only one element long, but you could pass
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159 * more than one scanline at a time if that's more convenient.
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160 */
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161 row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride];
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162 (void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
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163 }
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164
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165 /* Step 6: Finish compression */
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166
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167 jpeg_finish_compress(&cinfo);
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168 /* After finish_compress, we can close the output file. */
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169 fclose(outfile);
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170
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171 /* Step 7: release JPEG compression object */
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172
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173 /* This is an important step since it will release a good deal of memory. */
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174 jpeg_destroy_compress(&cinfo);
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175
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176 /* And we're done! */
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177 }
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178
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179
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180 /*
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181 * SOME FINE POINTS:
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182 *
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183 * In the above loop, we ignored the return value of jpeg_write_scanlines,
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184 * which is the number of scanlines actually written. We could get away
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185 * with this because we were only relying on the value of cinfo.next_scanline,
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186 * which will be incremented correctly. If you maintain additional loop
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187 * variables then you should be careful to increment them properly.
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188 * Actually, for output to a stdio stream you needn't worry, because
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189 * then jpeg_write_scanlines will write all the lines passed (or else exit
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190 * with a fatal error). Partial writes can only occur if you use a data
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191 * destination module that can demand suspension of the compressor.
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192 * (If you don't know what that's for, you don't need it.)
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193 *
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194 * If the compressor requires full-image buffers (for entropy-coding
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195 * optimization or a multi-scan JPEG file), it will create temporary
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196 * files for anything that doesn't fit within the maximum-memory setting.
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197 * (Note that temp files are NOT needed if you use the default parameters.)
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198 * On some systems you may need to set up a signal handler to ensure that
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199 * temporary files are deleted if the program is interrupted. See libjpeg.txt.
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200 *
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201 * Scanlines MUST be supplied in top-to-bottom order if you want your JPEG
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202 * files to be compatible with everyone else's. If you cannot readily read
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203 * your data in that order, you'll need an intermediate array to hold the
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204 * image. See rdtarga.c or rdbmp.c for examples of handling bottom-to-top
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205 * source data using the JPEG code's internal virtual-array mechanisms.
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206 */
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207
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208
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209
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210 /******************** JPEG DECOMPRESSION SAMPLE INTERFACE *******************/
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211
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212 /* This half of the example shows how to read data from the JPEG decompressor.
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213 * It's a bit more refined than the above, in that we show:
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214 * (a) how to modify the JPEG library's standard error-reporting behavior;
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215 * (b) how to allocate workspace using the library's memory manager.
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216 *
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217 * Just to make this example a little different from the first one, we'll
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218 * assume that we do not intend to put the whole image into an in-memory
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219 * buffer, but to send it line-by-line someplace else. We need a one-
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220 * scanline-high JSAMPLE array as a work buffer, and we will let the JPEG
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221 * memory manager allocate it for us. This approach is actually quite useful
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222 * because we don't need to remember to deallocate the buffer separately: it
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223 * will go away automatically when the JPEG object is cleaned up.
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224 */
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225
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226
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227 /*
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228 * ERROR HANDLING:
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229 *
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230 * The JPEG library's standard error handler (jerror.c) is divided into
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231 * several "methods" which you can override individually. This lets you
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232 * adjust the behavior without duplicating a lot of code, which you might
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233 * have to update with each future release.
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234 *
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235 * Our example here shows how to override the "error_exit" method so that
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236 * control is returned to the library's caller when a fatal error occurs,
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237 * rather than calling exit() as the standard error_exit method does.
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238 *
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239 * We use C's setjmp/longjmp facility to return control. This means that the
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240 * routine which calls the JPEG library must first execute a setjmp() call to
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241 * establish the return point. We want the replacement error_exit to do a
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242 * longjmp(). But we need to make the setjmp buffer accessible to the
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243 * error_exit routine. To do this, we make a private extension of the
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244 * standard JPEG error handler object. (If we were using C++, we'd say we
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245 * were making a subclass of the regular error handler.)
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246 *
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247 * Here's the extended error handler struct:
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248 */
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249
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250 struct my_error_mgr {
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251 struct jpeg_error_mgr pub; /* "public" fields */
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252
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253 jmp_buf setjmp_buffer; /* for return to caller */
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254 };
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255
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256 typedef struct my_error_mgr * my_error_ptr;
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257
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258 /*
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259 * Here's the routine that will replace the standard error_exit method:
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260 */
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261
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262 METHODDEF(void)
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263 my_error_exit (j_common_ptr cinfo)
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264 {
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265 /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */
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266 my_error_ptr myerr = (my_error_ptr) cinfo->err;
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267
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268 /* Always display the message. */
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269 /* We could postpone this until after returning, if we chose. */
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270 (*cinfo->err->output_message) (cinfo);
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271
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272 /* Return control to the setjmp point */
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273 longjmp(myerr->setjmp_buffer, 1);
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274 }
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275
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276
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277 /*
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278 * Sample routine for JPEG decompression. We assume that the source file name
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279 * is passed in. We want to return 1 on success, 0 on error.
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280 */
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281
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282
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283 GLOBAL(int)
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284 read_JPEG_file (char * filename)
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285 {
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286 /* This struct contains the JPEG decompression parameters and pointers to
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287 * working space (which is allocated as needed by the JPEG library).
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288 */
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289 struct jpeg_decompress_struct cinfo;
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290 /* We use our private extension JPEG error handler.
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291 * Note that this struct must live as long as the main JPEG parameter
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292 * struct, to avoid dangling-pointer problems.
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293 */
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294 struct my_error_mgr jerr;
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295 /* More stuff */
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296 FILE * infile; /* source file */
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297 JSAMPARRAY buffer; /* Output row buffer */
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298 int row_stride; /* physical row width in output buffer */
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299
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parents:
diff changeset
300 /* In this example we want to open the input file before doing anything else,
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
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parents:
diff changeset
301 * so that the setjmp() error recovery below can assume the file is open.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
302 * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
303 * requires it in order to read binary files.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
304 */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
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parents:
diff changeset
305
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parents:
diff changeset
306 if ((infile = fopen(filename, "rb")) == NULL) {
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
307 fprintf(stderr, "can't open %s\n", filename);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
308 return 0;
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
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parents:
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309 }
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parents:
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310
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
311 /* Step 1: allocate and initialize JPEG decompression object */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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312
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
313 /* We set up the normal JPEG error routines, then override error_exit. */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
314 cinfo.err = jpeg_std_error(&jerr.pub);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
315 jerr.pub.error_exit = my_error_exit;
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
316 /* Establish the setjmp return context for my_error_exit to use. */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
317 if (setjmp(jerr.setjmp_buffer)) {
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
318 /* If we get here, the JPEG code has signaled an error.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
319 * We need to clean up the JPEG object, close the input file, and return.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
320 */
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
321 jpeg_destroy_decompress(&cinfo);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
322 fclose(infile);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
323 return 0;
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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324 }
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
325 /* Now we can initialize the JPEG decompression object. */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
326 jpeg_create_decompress(&cinfo);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
327
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
328 /* Step 2: specify data source (eg, a file) */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
329
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parents:
diff changeset
330 jpeg_stdio_src(&cinfo, infile);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
331
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
332 /* Step 3: read file parameters with jpeg_read_header() */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
333
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
334 (void) jpeg_read_header(&cinfo, TRUE);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
335 /* We can ignore the return value from jpeg_read_header since
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
336 * (a) suspension is not possible with the stdio data source, and
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
337 * (b) we passed TRUE to reject a tables-only JPEG file as an error.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
338 * See libjpeg.txt for more info.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
339 */
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
340
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
341 /* Step 4: set parameters for decompression */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
342
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
343 /* In this example, we don't need to change any of the defaults set by
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
344 * jpeg_read_header(), so we do nothing here.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
345 */
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
346
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
347 /* Step 5: Start decompressor */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
348
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
349 (void) jpeg_start_decompress(&cinfo);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
350 /* We can ignore the return value since suspension is not possible
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
351 * with the stdio data source.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
352 */
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Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
353
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
354 /* We may need to do some setup of our own at this point before reading
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
355 * the data. After jpeg_start_decompress() we have the correct scaled
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
356 * output image dimensions available, as well as the output colormap
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
357 * if we asked for color quantization.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
358 * In this example, we need to make an output work buffer of the right size.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
359 */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
360 /* JSAMPLEs per row in output buffer */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
361 row_stride = cinfo.output_width * cinfo.output_components;
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
362 /* Make a one-row-high sample array that will go away when done with image */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
363 buffer = (*cinfo.mem->alloc_sarray)
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
364 ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
365
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
366 /* Step 6: while (scan lines remain to be read) */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
367 /* jpeg_read_scanlines(...); */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
368
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
369 /* Here we use the library's state variable cinfo.output_scanline as the
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
370 * loop counter, so that we don't have to keep track ourselves.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
371 */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
372 while (cinfo.output_scanline < cinfo.output_height) {
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
373 /* jpeg_read_scanlines expects an array of pointers to scanlines.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
374 * Here the array is only one element long, but you could ask for
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
375 * more than one scanline at a time if that's more convenient.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
376 */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
377 (void) jpeg_read_scanlines(&cinfo, buffer, 1);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
378 /* Assume put_scanline_someplace wants a pointer and sample count. */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
379 put_scanline_someplace(buffer[0], row_stride);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
380 }
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
381
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
382 /* Step 7: Finish decompression */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
383
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
384 (void) jpeg_finish_decompress(&cinfo);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
385 /* We can ignore the return value since suspension is not possible
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
386 * with the stdio data source.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
387 */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
388
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
389 /* Step 8: Release JPEG decompression object */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
390
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
391 /* This is an important step since it will release a good deal of memory. */
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
392 jpeg_destroy_decompress(&cinfo);
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
393
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
394 /* After finish_decompress, we can close the input file.
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
395 * Here we postpone it until after no more JPEG errors are possible,
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
396 * so as to simplify the setjmp error logic above. (Actually, I don't
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
diff changeset
397 * think that jpeg_destroy can do an error exit, but why assume anything...)
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
Franz Glasner <fzglas.hg@dom66.de>
parents:
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398 */
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399 fclose(infile);
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400
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401 /* At this point you may want to check to see whether any corrupt-data
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402 * warnings occurred (test whether jerr.pub.num_warnings is nonzero).
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403 */
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404
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405 /* And we're done! */
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406 return 1;
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407 }
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408
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409
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410 /*
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411 * SOME FINE POINTS:
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412 *
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413 * In the above code, we ignored the return value of jpeg_read_scanlines,
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414 * which is the number of scanlines actually read. We could get away with
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415 * this because we asked for only one line at a time and we weren't using
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416 * a suspending data source. See libjpeg.txt for more info.
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417 *
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418 * We cheated a bit by calling alloc_sarray() after jpeg_start_decompress();
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419 * we should have done it beforehand to ensure that the space would be
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420 * counted against the JPEG max_memory setting. In some systems the above
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421 * code would risk an out-of-memory error. However, in general we don't
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422 * know the output image dimensions before jpeg_start_decompress(), unless we
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423 * call jpeg_calc_output_dimensions(). See libjpeg.txt for more about this.
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424 *
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425 * Scanlines are returned in the same order as they appear in the JPEG file,
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426 * which is standardly top-to-bottom. If you must emit data bottom-to-top,
b50eed0cc0ef ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4.
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427 * you can use one of the virtual arrays provided by the JPEG memory manager
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428 * to invert the data. See wrbmp.c for an example.
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429 *
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430 * As with compression, some operating modes may require temporary files.
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431 * On some systems you may need to set up a signal handler to ensure that
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432 * temporary files are deleted if the program is interrupted. See libjpeg.txt.
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433 */