extractdct.c

/*Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted.*/

#include <stdio.h>
#include "jpeglib.h"

int main() {
    struct jpeg_decompress_struct srcinfo;
    struct jpeg_error_mgr srcerr;
    jvirt_barray_ptr *coef;
    JBLOCKARRAY coef_array;
    int c;
    JDIMENSION n_rows, n_cols, y, x;

    srcinfo.err = jpeg_std_error(&srcerr);
    jpeg_create_decompress(&srcinfo);
    jpeg_stdio_src(&srcinfo, stdin);
    jpeg_read_header(&srcinfo, TRUE);
    coef = jpeg_read_coefficients(&srcinfo);

    for (c = 0; c < srcinfo.num_components; c++) {
        n_rows = srcinfo.comp_info[c].height_in_blocks;
        n_cols = srcinfo.comp_info[c].width_in_blocks;
        for (y = 0; y < n_rows; y++) {
            coef_array = (*srcinfo.mem->access_virt_barray)((j_common_ptr) &srcinfo, coef[c], y, 1, FALSE);
            for (x = 0; x < n_cols; x++) {
                if (fwrite(coef_array[0][x], sizeof(JCOEF), DCTSIZE2, stdout) != DCTSIZE2) {
                    fprintf(stderr, "Error writing coefficients\n");
                }
            }
        }
    }

    jpeg_finish_decompress(&srcinfo);
    jpeg_destroy_decompress(&srcinfo);

    return 0;
}