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1 /* | 1 /* |
2 * example.c | 2 * example.c |
3 * | 3 * |
4 * This file illustrates how to use the IJG code as a subroutine library | 4 * This file illustrates how to use the IJG code as a subroutine library |
5 * to read or write JPEG image files. You should look at this code in | 5 * to read or write JPEG image files. You should look at this code in |
6 * conjunction with the documentation file libjpeg.txt. | 6 * conjunction with the documentation file libjpeg.txt. |
7 * | 7 * |
8 * This code will not do anything useful as-is, but it may be helpful as a | 8 * This code will not do anything useful as-is, but it may be helpful as a |
9 * skeleton for constructing routines that call the JPEG library. | 9 * skeleton for constructing routines that call the JPEG library. |
10 * | 10 * |
11 * We present these routines in the same coding style used in the JPEG code | 11 * We present these routines in the same coding style used in the JPEG code |
12 * (ANSI function definitions, etc); but you are of course free to code your | 12 * (ANSI function definitions, etc); but you are of course free to code your |
13 * routines in a different style if you prefer. | 13 * routines in a different style if you prefer. |
14 */ | 14 */ |
15 | 15 |
16 #include <stdio.h> | 16 #include <stdio.h> |
17 | 17 |
18 /* | 18 /* |
19 * Include file for users of JPEG library. | 19 * Include file for users of JPEG library. |
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51 * If you are working with color data, then the color values for each pixel | 51 * If you are working with color data, then the color values for each pixel |
52 * must be adjacent in the row; for example, R,G,B,R,G,B,R,G,B,... for 24-bit | 52 * must be adjacent in the row; for example, R,G,B,R,G,B,R,G,B,... for 24-bit |
53 * RGB color. | 53 * RGB color. |
54 * | 54 * |
55 * For this example, we'll assume that this data structure matches the way | 55 * For this example, we'll assume that this data structure matches the way |
56 * our application has stored the image in memory, so we can just pass a | 56 * our application has stored the image in memory, so we can just pass a |
57 * pointer to our image buffer. In particular, let's say that the image is | 57 * pointer to our image buffer. In particular, let's say that the image is |
58 * RGB color and is described by: | 58 * RGB color and is described by: |
59 */ | 59 */ |
60 | 60 |
61 extern JSAMPLE * image_buffer;» /* Points to large array of R,G,B-order data */ | 61 extern JSAMPLE *image_buffer; /* Points to large array of R,G,B-order data */ |
62 extern int image_height;» /* Number of rows in image */ | 62 extern int image_height; /* Number of rows in image */ |
63 extern int image_width;»» /* Number of columns in image */ | 63 extern int image_width; /* Number of columns in image */ |
64 | 64 |
65 | 65 |
66 /* | 66 /* |
67 * Sample routine for JPEG compression. We assume that the target file name | 67 * Sample routine for JPEG compression. We assume that the target file name |
68 * and a compression quality factor are passed in. | 68 * and a compression quality factor are passed in. |
69 */ | 69 */ |
70 | 70 |
71 GLOBAL(void) | 71 GLOBAL(void) |
72 write_JPEG_file (char * filename, int quality) | 72 write_JPEG_file (char *filename, int quality) |
73 { | 73 { |
74 /* This struct contains the JPEG compression parameters and pointers to | 74 /* This struct contains the JPEG compression parameters and pointers to |
75 * working space (which is allocated as needed by the JPEG library). | 75 * working space (which is allocated as needed by the JPEG library). |
76 * It is possible to have several such structures, representing multiple | 76 * It is possible to have several such structures, representing multiple |
77 * compression/decompression processes, in existence at once. We refer | 77 * compression/decompression processes, in existence at once. We refer |
78 * to any one struct (and its associated working data) as a "JPEG object". | 78 * to any one struct (and its associated working data) as a "JPEG object". |
79 */ | 79 */ |
80 struct jpeg_compress_struct cinfo; | 80 struct jpeg_compress_struct cinfo; |
81 /* This struct represents a JPEG error handler. It is declared separately | 81 /* This struct represents a JPEG error handler. It is declared separately |
82 * because applications often want to supply a specialized error handler | 82 * because applications often want to supply a specialized error handler |
83 * (see the second half of this file for an example). But here we just | 83 * (see the second half of this file for an example). But here we just |
84 * take the easy way out and use the standard error handler, which will | 84 * take the easy way out and use the standard error handler, which will |
85 * print a message on stderr and call exit() if compression fails. | 85 * print a message on stderr and call exit() if compression fails. |
86 * Note that this struct must live as long as the main JPEG parameter | 86 * Note that this struct must live as long as the main JPEG parameter |
87 * struct, to avoid dangling-pointer problems. | 87 * struct, to avoid dangling-pointer problems. |
88 */ | 88 */ |
89 struct jpeg_error_mgr jerr; | 89 struct jpeg_error_mgr jerr; |
90 /* More stuff */ | 90 /* More stuff */ |
91 FILE * outfile;» » /* target file */ | 91 FILE *outfile; /* target file */ |
92 JSAMPROW row_pointer[1];» /* pointer to JSAMPLE row[s] */ | 92 JSAMPROW row_pointer[1]; /* pointer to JSAMPLE row[s] */ |
93 int row_stride;» » /* physical row width in image buffer */ | 93 int row_stride; /* physical row width in image buffer */ |
94 | 94 |
95 /* Step 1: allocate and initialize JPEG compression object */ | 95 /* Step 1: allocate and initialize JPEG compression object */ |
96 | 96 |
97 /* We have to set up the error handler first, in case the initialization | 97 /* We have to set up the error handler first, in case the initialization |
98 * step fails. (Unlikely, but it could happen if you are out of memory.) | 98 * step fails. (Unlikely, but it could happen if you are out of memory.) |
99 * This routine fills in the contents of struct jerr, and returns jerr's | 99 * This routine fills in the contents of struct jerr, and returns jerr's |
100 * address which we place into the link field in cinfo. | 100 * address which we place into the link field in cinfo. |
101 */ | 101 */ |
102 cinfo.err = jpeg_std_error(&jerr); | 102 cinfo.err = jpeg_std_error(&jerr); |
103 /* Now we can initialize the JPEG compression object. */ | 103 /* Now we can initialize the JPEG compression object. */ |
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115 fprintf(stderr, "can't open %s\n", filename); | 115 fprintf(stderr, "can't open %s\n", filename); |
116 exit(1); | 116 exit(1); |
117 } | 117 } |
118 jpeg_stdio_dest(&cinfo, outfile); | 118 jpeg_stdio_dest(&cinfo, outfile); |
119 | 119 |
120 /* Step 3: set parameters for compression */ | 120 /* Step 3: set parameters for compression */ |
121 | 121 |
122 /* First we supply a description of the input image. | 122 /* First we supply a description of the input image. |
123 * Four fields of the cinfo struct must be filled in: | 123 * Four fields of the cinfo struct must be filled in: |
124 */ | 124 */ |
125 cinfo.image_width = image_width; » /* image width and height, in pixels */ | 125 cinfo.image_width = image_width; /* image width and height, in pixels */ |
126 cinfo.image_height = image_height; | 126 cinfo.image_height = image_height; |
127 cinfo.input_components = 3;» » /* # of color components per pixel */ | 127 cinfo.input_components = 3; /* # of color components per pixel */ |
128 cinfo.in_color_space = JCS_RGB; » /* colorspace of input image */ | 128 cinfo.in_color_space = JCS_RGB; /* colorspace of input image */ |
129 /* Now use the library's routine to set default compression parameters. | 129 /* Now use the library's routine to set default compression parameters. |
130 * (You must set at least cinfo.in_color_space before calling this, | 130 * (You must set at least cinfo.in_color_space before calling this, |
131 * since the defaults depend on the source color space.) | 131 * since the defaults depend on the source color space.) |
132 */ | 132 */ |
133 jpeg_set_defaults(&cinfo); | 133 jpeg_set_defaults(&cinfo); |
134 /* Now you can set any non-default parameters you wish to. | 134 /* Now you can set any non-default parameters you wish to. |
135 * Here we just illustrate the use of quality (quantization table) scaling: | 135 * Here we just illustrate the use of quality (quantization table) scaling: |
136 */ | 136 */ |
137 jpeg_set_quality(&cinfo, quality, TRUE /* limit to baseline-JPEG values */); | 137 jpeg_set_quality(&cinfo, quality, TRUE /* limit to baseline-JPEG values */); |
138 | 138 |
139 /* Step 4: Start compressor */ | 139 /* Step 4: Start compressor */ |
140 | 140 |
141 /* TRUE ensures that we will write a complete interchange-JPEG file. | 141 /* TRUE ensures that we will write a complete interchange-JPEG file. |
142 * Pass TRUE unless you are very sure of what you're doing. | 142 * Pass TRUE unless you are very sure of what you're doing. |
143 */ | 143 */ |
144 jpeg_start_compress(&cinfo, TRUE); | 144 jpeg_start_compress(&cinfo, TRUE); |
145 | 145 |
146 /* Step 5: while (scan lines remain to be written) */ | 146 /* Step 5: while (scan lines remain to be written) */ |
147 /* jpeg_write_scanlines(...); */ | 147 /* jpeg_write_scanlines(...); */ |
148 | 148 |
149 /* Here we use the library's state variable cinfo.next_scanline as the | 149 /* Here we use the library's state variable cinfo.next_scanline as the |
150 * loop counter, so that we don't have to keep track ourselves. | 150 * loop counter, so that we don't have to keep track ourselves. |
151 * To keep things simple, we pass one scanline per call; you can pass | 151 * To keep things simple, we pass one scanline per call; you can pass |
152 * more if you wish, though. | 152 * more if you wish, though. |
153 */ | 153 */ |
154 row_stride = image_width * 3;»/* JSAMPLEs per row in image_buffer */ | 154 row_stride = image_width * 3; /* JSAMPLEs per row in image_buffer */ |
155 | 155 |
156 while (cinfo.next_scanline < cinfo.image_height) { | 156 while (cinfo.next_scanline < cinfo.image_height) { |
157 /* jpeg_write_scanlines expects an array of pointers to scanlines. | 157 /* jpeg_write_scanlines expects an array of pointers to scanlines. |
158 * Here the array is only one element long, but you could pass | 158 * Here the array is only one element long, but you could pass |
159 * more than one scanline at a time if that's more convenient. | 159 * more than one scanline at a time if that's more convenient. |
160 */ | 160 */ |
161 row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride]; | 161 row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride]; |
162 (void) jpeg_write_scanlines(&cinfo, row_pointer, 1); | 162 (void) jpeg_write_scanlines(&cinfo, row_pointer, 1); |
163 } | 163 } |
164 | 164 |
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241 * establish the return point. We want the replacement error_exit to do a | 241 * establish the return point. We want the replacement error_exit to do a |
242 * longjmp(). But we need to make the setjmp buffer accessible to the | 242 * longjmp(). But we need to make the setjmp buffer accessible to the |
243 * error_exit routine. To do this, we make a private extension of the | 243 * error_exit routine. To do this, we make a private extension of the |
244 * standard JPEG error handler object. (If we were using C++, we'd say we | 244 * standard JPEG error handler object. (If we were using C++, we'd say we |
245 * were making a subclass of the regular error handler.) | 245 * were making a subclass of the regular error handler.) |
246 * | 246 * |
247 * Here's the extended error handler struct: | 247 * Here's the extended error handler struct: |
248 */ | 248 */ |
249 | 249 |
250 struct my_error_mgr { | 250 struct my_error_mgr { |
251 struct jpeg_error_mgr pub;» /* "public" fields */ | 251 struct jpeg_error_mgr pub; /* "public" fields */ |
252 | 252 |
253 jmp_buf setjmp_buffer;» /* for return to caller */ | 253 jmp_buf setjmp_buffer; /* for return to caller */ |
254 }; | 254 }; |
255 | 255 |
256 typedef struct my_error_mgr * my_error_ptr; | 256 typedef struct my_error_mgr *my_error_ptr; |
257 | 257 |
258 /* | 258 /* |
259 * Here's the routine that will replace the standard error_exit method: | 259 * Here's the routine that will replace the standard error_exit method: |
260 */ | 260 */ |
261 | 261 |
262 METHODDEF(void) | 262 METHODDEF(void) |
263 my_error_exit (j_common_ptr cinfo) | 263 my_error_exit (j_common_ptr cinfo) |
264 { | 264 { |
265 /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */ | 265 /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */ |
266 my_error_ptr myerr = (my_error_ptr) cinfo->err; | 266 my_error_ptr myerr = (my_error_ptr) cinfo->err; |
267 | 267 |
268 /* Always display the message. */ | 268 /* Always display the message. */ |
269 /* We could postpone this until after returning, if we chose. */ | 269 /* We could postpone this until after returning, if we chose. */ |
270 (*cinfo->err->output_message) (cinfo); | 270 (*cinfo->err->output_message) (cinfo); |
271 | 271 |
272 /* Return control to the setjmp point */ | 272 /* Return control to the setjmp point */ |
273 longjmp(myerr->setjmp_buffer, 1); | 273 longjmp(myerr->setjmp_buffer, 1); |
274 } | 274 } |
275 | 275 |
276 | 276 |
277 /* | 277 /* |
278 * Sample routine for JPEG decompression. We assume that the source file name | 278 * Sample routine for JPEG decompression. We assume that the source file name |
279 * is passed in. We want to return 1 on success, 0 on error. | 279 * is passed in. We want to return 1 on success, 0 on error. |
280 */ | 280 */ |
281 | 281 |
282 | 282 |
283 GLOBAL(int) | 283 GLOBAL(int) |
284 read_JPEG_file (char * filename) | 284 read_JPEG_file (char *filename) |
285 { | 285 { |
286 /* This struct contains the JPEG decompression parameters and pointers to | 286 /* This struct contains the JPEG decompression parameters and pointers to |
287 * working space (which is allocated as needed by the JPEG library). | 287 * working space (which is allocated as needed by the JPEG library). |
288 */ | 288 */ |
289 struct jpeg_decompress_struct cinfo; | 289 struct jpeg_decompress_struct cinfo; |
290 /* We use our private extension JPEG error handler. | 290 /* We use our private extension JPEG error handler. |
291 * Note that this struct must live as long as the main JPEG parameter | 291 * Note that this struct must live as long as the main JPEG parameter |
292 * struct, to avoid dangling-pointer problems. | 292 * struct, to avoid dangling-pointer problems. |
293 */ | 293 */ |
294 struct my_error_mgr jerr; | 294 struct my_error_mgr jerr; |
295 /* More stuff */ | 295 /* More stuff */ |
296 FILE * infile;» » /* source file */ | 296 FILE *infile; /* source file */ |
297 JSAMPARRAY buffer;» » /* Output row buffer */ | 297 JSAMPARRAY buffer; /* Output row buffer */ |
298 int row_stride;» » /* physical row width in output buffer */ | 298 int row_stride; /* physical row width in output buffer */ |
299 | 299 |
300 /* In this example we want to open the input file before doing anything else, | 300 /* In this example we want to open the input file before doing anything else, |
301 * so that the setjmp() error recovery below can assume the file is open. | 301 * so that the setjmp() error recovery below can assume the file is open. |
302 * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that | 302 * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that |
303 * requires it in order to read binary files. | 303 * requires it in order to read binary files. |
304 */ | 304 */ |
305 | 305 |
306 if ((infile = fopen(filename, "rb")) == NULL) { | 306 if ((infile = fopen(filename, "rb")) == NULL) { |
307 fprintf(stderr, "can't open %s\n", filename); | 307 fprintf(stderr, "can't open %s\n", filename); |
308 return 0; | 308 return 0; |
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349 (void) jpeg_start_decompress(&cinfo); | 349 (void) jpeg_start_decompress(&cinfo); |
350 /* We can ignore the return value since suspension is not possible | 350 /* We can ignore the return value since suspension is not possible |
351 * with the stdio data source. | 351 * with the stdio data source. |
352 */ | 352 */ |
353 | 353 |
354 /* We may need to do some setup of our own at this point before reading | 354 /* We may need to do some setup of our own at this point before reading |
355 * the data. After jpeg_start_decompress() we have the correct scaled | 355 * the data. After jpeg_start_decompress() we have the correct scaled |
356 * output image dimensions available, as well as the output colormap | 356 * output image dimensions available, as well as the output colormap |
357 * if we asked for color quantization. | 357 * if we asked for color quantization. |
358 * In this example, we need to make an output work buffer of the right size. | 358 * In this example, we need to make an output work buffer of the right size. |
359 */ | 359 */ |
360 /* JSAMPLEs per row in output buffer */ | 360 /* JSAMPLEs per row in output buffer */ |
361 row_stride = cinfo.output_width * cinfo.output_components; | 361 row_stride = cinfo.output_width * cinfo.output_components; |
362 /* Make a one-row-high sample array that will go away when done with image */ | 362 /* Make a one-row-high sample array that will go away when done with image */ |
363 buffer = (*cinfo.mem->alloc_sarray) | 363 buffer = (*cinfo.mem->alloc_sarray) |
364 » » ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1); | 364 ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1); |
365 | 365 |
366 /* Step 6: while (scan lines remain to be read) */ | 366 /* Step 6: while (scan lines remain to be read) */ |
367 /* jpeg_read_scanlines(...); */ | 367 /* jpeg_read_scanlines(...); */ |
368 | 368 |
369 /* Here we use the library's state variable cinfo.output_scanline as the | 369 /* Here we use the library's state variable cinfo.output_scanline as the |
370 * loop counter, so that we don't have to keep track ourselves. | 370 * loop counter, so that we don't have to keep track ourselves. |
371 */ | 371 */ |
372 while (cinfo.output_scanline < cinfo.output_height) { | 372 while (cinfo.output_scanline < cinfo.output_height) { |
373 /* jpeg_read_scanlines expects an array of pointers to scanlines. | 373 /* jpeg_read_scanlines expects an array of pointers to scanlines. |
374 * Here the array is only one element long, but you could ask for | 374 * Here the array is only one element long, but you could ask for |
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424 * | 424 * |
425 * Scanlines are returned in the same order as they appear in the JPEG file, | 425 * Scanlines are returned in the same order as they appear in the JPEG file, |
426 * which is standardly top-to-bottom. If you must emit data bottom-to-top, | 426 * which is standardly top-to-bottom. If you must emit data bottom-to-top, |
427 * you can use one of the virtual arrays provided by the JPEG memory manager | 427 * you can use one of the virtual arrays provided by the JPEG memory manager |
428 * to invert the data. See wrbmp.c for an example. | 428 * to invert the data. See wrbmp.c for an example. |
429 * | 429 * |
430 * As with compression, some operating modes may require temporary files. | 430 * As with compression, some operating modes may require temporary files. |
431 * On some systems you may need to set up a signal handler to ensure that | 431 * On some systems you may need to set up a signal handler to ensure that |
432 * temporary files are deleted if the program is interrupted. See libjpeg.txt. | 432 * temporary files are deleted if the program is interrupted. See libjpeg.txt. |
433 */ | 433 */ |
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