replacedct.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(int argc, char **argv) {
    struct jpeg_decompress_struct srcinfo;
    struct jpeg_compress_struct dstinfo;
    struct jpeg_error_mgr srcerr, dsterr;
    jvirt_barray_ptr *coef;
    char *coef_filename;
    FILE *coef_file;
    JBLOCKARRAY coef_array;
    int c;
    JDIMENSION n_rows, n_cols, y, x;

    if (argc < 2) {
        fprintf(stderr, "Usage: replacedct coef_file < input.jpg > output.jpg\n");
        return 1;
    }
    coef_filename = argv[1];

    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);

    coef_file = fopen(coef_filename, "rb");
    if (coef_file == NULL) {
        fprintf(stderr, "Error opening file: %s\n", coef_filename);
        return 1;
    }

    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, TRUE);
            for (x = 0; x < n_cols; x++) {
                if (fread(coef_array[0][x], sizeof(JCOEF), DCTSIZE2, coef_file) != DCTSIZE2) {
                    fprintf(stderr, "Error reading coefficients\n");
                    fclose(coef_file);
                    return 1;
                }
            }
        }
    }

    dstinfo.err = jpeg_std_error(&dsterr);
    jpeg_create_compress(&dstinfo);
    jpeg_stdio_dest(&dstinfo, stdout);
    jpeg_copy_critical_parameters(&srcinfo, &dstinfo);
    jpeg_write_coefficients(&dstinfo, coef);

    jpeg_finish_compress(&dstinfo);
    jpeg_destroy_compress(&dstinfo);
    jpeg_finish_decompress(&srcinfo);
    jpeg_destroy_decompress(&srcinfo);
    fclose(coef_file);

    return 0;
}