SCAN_header
if (!decode_jpeg_header(j, SCAN_header))
if (scan == SCAN_header) return 1;
if (scan == SCAN_header) { s->img_n = 4; return 1; }
if (scan == SCAN_header) { s->img_n = pal_img_n; return 1; }
if (!parse_png_file(p, SCAN_header, 0))