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Diffstat (limited to 'jpg/example.c')
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diff --git a/jpg/example.c b/jpg/example.c deleted file mode 100644 index 1d6f6cc..0000000 --- a/jpg/example.c +++ /dev/null @@ -1,433 +0,0 @@ -/* - * example.c - * - * This file illustrates how to use the IJG code as a subroutine library - * to read or write JPEG image files. You should look at this code in - * conjunction with the documentation file libjpeg.txt. - * - * This code will not do anything useful as-is, but it may be helpful as a - * skeleton for constructing routines that call the JPEG library. - * - * We present these routines in the same coding style used in the JPEG code - * (ANSI function definitions, etc); but you are of course free to code your - * routines in a different style if you prefer. - */ - -#include <stdio.h> - -/* - * Include file for users of JPEG library. - * You will need to have included system headers that define at least - * the typedefs FILE and size_t before you can include jpeglib.h. - * (stdio.h is sufficient on ANSI-conforming systems.) - * You may also wish to include "jerror.h". - */ - -#include "jpeglib.h" - -/* - * <setjmp.h> is used for the optional error recovery mechanism shown in - * the second part of the example. - */ - -#include <setjmp.h> - - - -/******************** JPEG COMPRESSION SAMPLE INTERFACE *******************/ - -/* This half of the example shows how to feed data into the JPEG compressor. - * We present a minimal version that does not worry about refinements such - * as error recovery (the JPEG code will just exit() if it gets an error). - */ - - -/* - * IMAGE DATA FORMATS: - * - * The standard input image format is a rectangular array of pixels, with - * each pixel having the same number of "component" values (color channels). - * Each pixel row is an array of JSAMPLEs (which typically are unsigned chars). - * If you are working with color data, then the color values for each pixel - * must be adjacent in the row; for example, R,G,B,R,G,B,R,G,B,... for 24-bit - * RGB color. - * - * For this example, we'll assume that this data structure matches the way - * our application has stored the image in memory, so we can just pass a - * pointer to our image buffer. In particular, let's say that the image is - * RGB color and is described by: - */ - -extern JSAMPLE * image_buffer; /* Points to large array of R,G,B-order data */ -extern int image_height; /* Number of rows in image */ -extern int image_width; /* Number of columns in image */ - - -/* - * Sample routine for JPEG compression. We assume that the target file name - * and a compression quality factor are passed in. - */ - -GLOBAL(void) -write_JPEG_file (char * filename, int quality) -{ - /* This struct contains the JPEG compression parameters and pointers to - * working space (which is allocated as needed by the JPEG library). - * It is possible to have several such structures, representing multiple - * compression/decompression processes, in existence at once. We refer - * to any one struct (and its associated working data) as a "JPEG object". - */ - struct jpeg_compress_struct cinfo; - /* This struct represents a JPEG error handler. It is declared separately - * because applications often want to supply a specialized error handler - * (see the second half of this file for an example). But here we just - * take the easy way out and use the standard error handler, which will - * print a message on stderr and call exit() if compression fails. - * Note that this struct must live as long as the main JPEG parameter - * struct, to avoid dangling-pointer problems. - */ - struct jpeg_error_mgr jerr; - /* More stuff */ - FILE * outfile; /* target file */ - JSAMPROW row_pointer[1]; /* pointer to JSAMPLE row[s] */ - int row_stride; /* physical row width in image buffer */ - - /* Step 1: allocate and initialize JPEG compression object */ - - /* We have to set up the error handler first, in case the initialization - * step fails. (Unlikely, but it could happen if you are out of memory.) - * This routine fills in the contents of struct jerr, and returns jerr's - * address which we place into the link field in cinfo. - */ - cinfo.err = jpeg_std_error(&jerr); - /* Now we can initialize the JPEG compression object. */ - jpeg_create_compress(&cinfo); - - /* Step 2: specify data destination (eg, a file) */ - /* Note: steps 2 and 3 can be done in either order. */ - - /* Here we use the library-supplied code to send compressed data to a - * stdio stream. You can also write your own code to do something else. - * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that - * requires it in order to write binary files. - */ - if ((outfile = fopen(filename, "wb")) == NULL) { - fprintf(stderr, "can't open %s\n", filename); - exit(1); - } - jpeg_stdio_dest(&cinfo, outfile); - - /* Step 3: set parameters for compression */ - - /* First we supply a description of the input image. - * Four fields of the cinfo struct must be filled in: - */ - cinfo.image_width = image_width; /* image width and height, in pixels */ - cinfo.image_height = image_height; - cinfo.input_components = 3; /* # of color components per pixel */ - cinfo.in_color_space = JCS_RGB; /* colorspace of input image */ - /* Now use the library's routine to set default compression parameters. - * (You must set at least cinfo.in_color_space before calling this, - * since the defaults depend on the source color space.) - */ - jpeg_set_defaults(&cinfo); - /* Now you can set any non-default parameters you wish to. - * Here we just illustrate the use of quality (quantization table) scaling: - */ - jpeg_set_quality(&cinfo, quality, TRUE /* limit to baseline-JPEG values */); - - /* Step 4: Start compressor */ - - /* TRUE ensures that we will write a complete interchange-JPEG file. - * Pass TRUE unless you are very sure of what you're doing. - */ - jpeg_start_compress(&cinfo, TRUE); - - /* Step 5: while (scan lines remain to be written) */ - /* jpeg_write_scanlines(...); */ - - /* Here we use the library's state variable cinfo.next_scanline as the - * loop counter, so that we don't have to keep track ourselves. - * To keep things simple, we pass one scanline per call; you can pass - * more if you wish, though. - */ - row_stride = image_width * 3; /* JSAMPLEs per row in image_buffer */ - - while (cinfo.next_scanline < cinfo.image_height) { - /* jpeg_write_scanlines expects an array of pointers to scanlines. - * Here the array is only one element long, but you could pass - * more than one scanline at a time if that's more convenient. - */ - row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride]; - (void) jpeg_write_scanlines(&cinfo, row_pointer, 1); - } - - /* Step 6: Finish compression */ - - jpeg_finish_compress(&cinfo); - /* After finish_compress, we can close the output file. */ - fclose(outfile); - - /* Step 7: release JPEG compression object */ - - /* This is an important step since it will release a good deal of memory. */ - jpeg_destroy_compress(&cinfo); - - /* And we're done! */ -} - - -/* - * SOME FINE POINTS: - * - * In the above loop, we ignored the return value of jpeg_write_scanlines, - * which is the number of scanlines actually written. We could get away - * with this because we were only relying on the value of cinfo.next_scanline, - * which will be incremented correctly. If you maintain additional loop - * variables then you should be careful to increment them properly. - * Actually, for output to a stdio stream you needn't worry, because - * then jpeg_write_scanlines will write all the lines passed (or else exit - * with a fatal error). Partial writes can only occur if you use a data - * destination module that can demand suspension of the compressor. - * (If you don't know what that's for, you don't need it.) - * - * If the compressor requires full-image buffers (for entropy-coding - * optimization or a multi-scan JPEG file), it will create temporary - * files for anything that doesn't fit within the maximum-memory setting. - * (Note that temp files are NOT needed if you use the default parameters.) - * On some systems you may need to set up a signal handler to ensure that - * temporary files are deleted if the program is interrupted. See libjpeg.txt. - * - * Scanlines MUST be supplied in top-to-bottom order if you want your JPEG - * files to be compatible with everyone else's. If you cannot readily read - * your data in that order, you'll need an intermediate array to hold the - * image. See rdtarga.c or rdbmp.c for examples of handling bottom-to-top - * source data using the JPEG code's internal virtual-array mechanisms. - */ - - - -/******************** JPEG DECOMPRESSION SAMPLE INTERFACE *******************/ - -/* This half of the example shows how to read data from the JPEG decompressor. - * It's a bit more refined than the above, in that we show: - * (a) how to modify the JPEG library's standard error-reporting behavior; - * (b) how to allocate workspace using the library's memory manager. - * - * Just to make this example a little different from the first one, we'll - * assume that we do not intend to put the whole image into an in-memory - * buffer, but to send it line-by-line someplace else. We need a one- - * scanline-high JSAMPLE array as a work buffer, and we will let the JPEG - * memory manager allocate it for us. This approach is actually quite useful - * because we don't need to remember to deallocate the buffer separately: it - * will go away automatically when the JPEG object is cleaned up. - */ - - -/* - * ERROR HANDLING: - * - * The JPEG library's standard error handler (jerror.c) is divided into - * several "methods" which you can override individually. This lets you - * adjust the behavior without duplicating a lot of code, which you might - * have to update with each future release. - * - * Our example here shows how to override the "error_exit" method so that - * control is returned to the library's caller when a fatal error occurs, - * rather than calling exit() as the standard error_exit method does. - * - * We use C's setjmp/longjmp facility to return control. This means that the - * routine which calls the JPEG library must first execute a setjmp() call to - * establish the return point. We want the replacement error_exit to do a - * longjmp(). But we need to make the setjmp buffer accessible to the - * error_exit routine. To do this, we make a private extension of the - * standard JPEG error handler object. (If we were using C++, we'd say we - * were making a subclass of the regular error handler.) - * - * Here's the extended error handler struct: - */ - -struct my_error_mgr { - struct jpeg_error_mgr pub; /* "public" fields */ - - jmp_buf setjmp_buffer; /* for return to caller */ -}; - -typedef struct my_error_mgr * my_error_ptr; - -/* - * Here's the routine that will replace the standard error_exit method: - */ - -METHODDEF(void) -my_error_exit (j_common_ptr cinfo) -{ - /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */ - my_error_ptr myerr = (my_error_ptr) cinfo->err; - - /* Always display the message. */ - /* We could postpone this until after returning, if we chose. */ - (*cinfo->err->output_message) (cinfo); - - /* Return control to the setjmp point */ - longjmp(myerr->setjmp_buffer, 1); -} - - -/* - * Sample routine for JPEG decompression. We assume that the source file name - * is passed in. We want to return 1 on success, 0 on error. - */ - - -GLOBAL(int) -read_JPEG_file (char * filename) -{ - /* This struct contains the JPEG decompression parameters and pointers to - * working space (which is allocated as needed by the JPEG library). - */ - struct jpeg_decompress_struct cinfo; - /* We use our private extension JPEG error handler. - * Note that this struct must live as long as the main JPEG parameter - * struct, to avoid dangling-pointer problems. - */ - struct my_error_mgr jerr; - /* More stuff */ - FILE * infile; /* source file */ - JSAMPARRAY buffer; /* Output row buffer */ - int row_stride; /* physical row width in output buffer */ - - /* In this example we want to open the input file before doing anything else, - * so that the setjmp() error recovery below can assume the file is open. - * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that - * requires it in order to read binary files. - */ - - if ((infile = fopen(filename, "rb")) == NULL) { - fprintf(stderr, "can't open %s\n", filename); - return 0; - } - - /* Step 1: allocate and initialize JPEG decompression object */ - - /* We set up the normal JPEG error routines, then override error_exit. */ - cinfo.err = jpeg_std_error(&jerr.pub); - jerr.pub.error_exit = my_error_exit; - /* Establish the setjmp return context for my_error_exit to use. */ - if (setjmp(jerr.setjmp_buffer)) { - /* If we get here, the JPEG code has signaled an error. - * We need to clean up the JPEG object, close the input file, and return. - */ - jpeg_destroy_decompress(&cinfo); - fclose(infile); - return 0; - } - /* Now we can initialize the JPEG decompression object. */ - jpeg_create_decompress(&cinfo); - - /* Step 2: specify data source (eg, a file) */ - - jpeg_stdio_src(&cinfo, infile); - - /* Step 3: read file parameters with jpeg_read_header() */ - - (void) jpeg_read_header(&cinfo, TRUE); - /* We can ignore the return value from jpeg_read_header since - * (a) suspension is not possible with the stdio data source, and - * (b) we passed TRUE to reject a tables-only JPEG file as an error. - * See libjpeg.txt for more info. - */ - - /* Step 4: set parameters for decompression */ - - /* In this example, we don't need to change any of the defaults set by - * jpeg_read_header(), so we do nothing here. - */ - - /* Step 5: Start decompressor */ - - (void) jpeg_start_decompress(&cinfo); - /* We can ignore the return value since suspension is not possible - * with the stdio data source. - */ - - /* We may need to do some setup of our own at this point before reading - * the data. After jpeg_start_decompress() we have the correct scaled - * output image dimensions available, as well as the output colormap - * if we asked for color quantization. - * In this example, we need to make an output work buffer of the right size. - */ - /* JSAMPLEs per row in output buffer */ - row_stride = cinfo.output_width * cinfo.output_components; - /* Make a one-row-high sample array that will go away when done with image */ - buffer = (*cinfo.mem->alloc_sarray) - ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1); - - /* Step 6: while (scan lines remain to be read) */ - /* jpeg_read_scanlines(...); */ - - /* Here we use the library's state variable cinfo.output_scanline as the - * loop counter, so that we don't have to keep track ourselves. - */ - while (cinfo.output_scanline < cinfo.output_height) { - /* jpeg_read_scanlines expects an array of pointers to scanlines. - * Here the array is only one element long, but you could ask for - * more than one scanline at a time if that's more convenient. - */ - (void) jpeg_read_scanlines(&cinfo, buffer, 1); - /* Assume put_scanline_someplace wants a pointer and sample count. */ - put_scanline_someplace(buffer[0], row_stride); - } - - /* Step 7: Finish decompression */ - - (void) jpeg_finish_decompress(&cinfo); - /* We can ignore the return value since suspension is not possible - * with the stdio data source. - */ - - /* Step 8: Release JPEG decompression object */ - - /* This is an important step since it will release a good deal of memory. */ - jpeg_destroy_decompress(&cinfo); - - /* After finish_decompress, we can close the input file. - * Here we postpone it until after no more JPEG errors are possible, - * so as to simplify the setjmp error logic above. (Actually, I don't - * think that jpeg_destroy can do an error exit, but why assume anything...) - */ - fclose(infile); - - /* At this point you may want to check to see whether any corrupt-data - * warnings occurred (test whether jerr.pub.num_warnings is nonzero). - */ - - /* And we're done! */ - return 1; -} - - -/* - * SOME FINE POINTS: - * - * In the above code, we ignored the return value of jpeg_read_scanlines, - * which is the number of scanlines actually read. We could get away with - * this because we asked for only one line at a time and we weren't using - * a suspending data source. See libjpeg.txt for more info. - * - * We cheated a bit by calling alloc_sarray() after jpeg_start_decompress(); - * we should have done it beforehand to ensure that the space would be - * counted against the JPEG max_memory setting. In some systems the above - * code would risk an out-of-memory error. However, in general we don't - * know the output image dimensions before jpeg_start_decompress(), unless we - * call jpeg_calc_output_dimensions(). See libjpeg.txt for more about this. - * - * Scanlines are returned in the same order as they appear in the JPEG file, - * which is standardly top-to-bottom. If you must emit data bottom-to-top, - * you can use one of the virtual arrays provided by the JPEG memory manager - * to invert the data. See wrbmp.c for an example. - * - * As with compression, some operating modes may require temporary files. - * On some systems you may need to set up a signal handler to ensure that - * temporary files are deleted if the program is interrupted. See libjpeg.txt. - */ |