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Write each scan from a multi-scan/progressive JPEG.
// jpeg_split.c: Write each scan from a multi-scan/progressive JPEG.
// This is based loosely on example.c from libjpeg, and should require only
// libjpeg as a dependency (e.g. gcc -ljpeg -o jpeg_split.o jpeg_split.c).
#include <stdio.h>
#include <jerror.h>
#include "jpeglib.h"
#include <setjmp.h>
#include <string.h>
void read_scan(struct jpeg_decompress_struct * cinfo,
JSAMPARRAY buffer,
char * base_output);
int read_JPEG_file (char * filename, int scanNumber, char * base_output);
int main(int argc, char **argv) {
if (argc < 3) {
printf("Usage: %s <Input JPEG> <Output base name>\n", argv[0]);
printf("This reads in the progressive/multi-scan JPEG given and writes out each scan\n");
printf("to a separate PPM file, named with the scan number.\n");
return 1;
}
char * fname = argv[1];
char * out_base = argv[2];
read_JPEG_file(fname, 1, out_base);
return 0;
}
struct error_mgr {
struct jpeg_error_mgr pub;
jmp_buf setjmp_buffer;
};
METHODDEF(void) error_exit (j_common_ptr cinfo) {
struct error_mgr * err = (struct error_mgr *) cinfo->err;
(*cinfo->err->output_message) (cinfo);
longjmp(err->setjmp_buffer, 1);
}
int read_JPEG_file (char * filename, int scanNumber, char * base_output) {
struct jpeg_decompress_struct cinfo;
struct error_mgr jerr;
FILE * infile; /* source file */
JSAMPARRAY buffer; /* Output row buffer */
int row_stride; /* physical row width in output buffer */
if ((infile = fopen(filename, "rb")) == NULL) {
fprintf(stderr, "can't open %s\n", filename);
return 0;
}
// Set up the normal JPEG error routines, then override error_exit.
cinfo.err = jpeg_std_error(&jerr.pub);
jerr.pub.error_exit = error_exit;
// Establish the setjmp return context for error_exit to use:
if (setjmp(jerr.setjmp_buffer)) {
jpeg_destroy_decompress(&cinfo);
fclose(infile);
return 0;
}
jpeg_create_decompress(&cinfo);
jpeg_stdio_src(&cinfo, infile);
(void) jpeg_read_header(&cinfo, TRUE);
// Set some decompression parameters
// Incremental reading requires this flag:
cinfo.buffered_image = TRUE;
// To perform fast scaling in the output, set these:
cinfo.scale_num = 1;
cinfo.scale_denom = 1;
// Decompression begins...
(void) jpeg_start_decompress(&cinfo);
printf("JPEG is %s-scan\n", jpeg_has_multiple_scans(&cinfo) ? "multi" : "single");
printf("Outputting %ix%i\n", cinfo.output_width, cinfo.output_height);
// row_stride = 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);
// Start actually handling image data!
while(!jpeg_input_complete(&cinfo)) {
read_scan(&cinfo, buffer, base_output);
}
// Clean up.
(void) jpeg_finish_decompress(&cinfo);
jpeg_destroy_decompress(&cinfo);
fclose(infile);
if (jerr.pub.num_warnings) {
printf("libjpeg indicates %i warnings\n", jerr.pub.num_warnings);
}
}
void read_scan(struct jpeg_decompress_struct * cinfo,
JSAMPARRAY buffer,
char * base_output)
{
char out_name[1024];
FILE * outfile = NULL;
int scan_num = 0;
scan_num = cinfo->input_scan_number;
jpeg_start_output(cinfo, scan_num);
// Read up to the next scan.
int status;
do {
status = jpeg_consume_input(cinfo);
} while (status != JPEG_REACHED_SOS && status != JPEG_REACHED_EOI);
// Construct a filename & write PPM image header.
snprintf(out_name, 1024, "%s%i.ppm", base_output, scan_num);
if ((outfile = fopen(out_name, "wb")) == NULL) {
fprintf(stderr, "Can't open %s for writing!\n", out_name);
return;
}
fprintf(outfile, "P6\n%d %d\n255\n", cinfo->output_width, cinfo->output_height);
// Read each scanline into 'buffer' and write it to the PPM.
// (Note that libjpeg updates cinfo->output_scanline automatically)
while (cinfo->output_scanline < cinfo->output_height) {
jpeg_read_scanlines(cinfo, buffer, 1);
fwrite(buffer[0], cinfo->output_components, cinfo->output_width, outfile);
}
jpeg_finish_output(cinfo);
fclose(outfile);
}
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