my $gd = $image->gd;
my( undef, $width, $height, undef, undef ) = unpack 'nnnCV', substr( $gd, 0, 11, '' );
my $len = length( $gd ) / 4 * 3;
my $bmp = pack 'a2 V V V l< l< l< v v V V l< l< V V',
    'BM', $len + 54, 0, 54, 40, $width, -$height, 1, 24, 0, $len, 0, 0, 0;

$bmp .= join'', unpack '(xaaa)*', $gd;