source: bootcd/isolinux/syslinux-6.03/utils/lss16toppm

#!/usr/bin/perl
## -----------------------------------------------------------------------
##
##   Copyright 2001-2008 H. Peter Anvin - All Rights Reserved
##
##   This program is free software; you can redistribute it and/or modify
##   it under the terms of the GNU General Public License as published by
##   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
##   Boston MA 02111-1307, USA; either version 2 of the License, or
##   (at your option) any later version; incorporated herein by reference.
##
## -----------------------------------------------------------------------

##
## lss16toppm:
## Convert an LSS-16 image to PPM
##
## Usage:
##
##      lss16toppm [-map] < file.lss > file.ppm
##
## The -map causes the color map to be output on stderr.
##

eval { use bytes; };
eval { binmode STDIN; };
eval { binmode STDOUT; };

$map = 0;
foreach $arg ( @ARGV ) {
    if ( $arg eq '-map' ) {
        $map = 1;
    } else {
        print STDERR "$0: Unknown option: $arg\n";
        exit 127;
    }
}

if ( read(STDIN, $header, 56) != 56 ) {
    print STDERR "$0: Short file\n";
    exit 1;
}

($magic, $xsize, $ysize, @colorset) = unpack("Vvvc48", $header);

if ( $magic != 0x1413f33d ) {
    print STDERR "$0: Invalid file format\n";
    exit 1;
}

%color = ();
for ( $i = 0 ; $i < 16 ; $i++ ) {
    $r = int((shift @colorset) * 255 / 63 + 0.5);
    $g = int((shift @colorset) * 255 / 63 + 0.5);
    $b = int((shift @colorset) * 255 / 63 + 0.5);

    $color{$i} = pack("ccc", $r, $g, $b);

    if ( $map ) {
        printf STDERR "#%02x%02x%02x=%d\n", $r, $g, $b, $i;
    }
}

sub get_nybble() {
    my($ch,$n);
    if ( defined($nybble_buf) ) {
        $n = $nybble_buf;
        undef $nybble_buf;
    } else {
        if ( read(STDIN, $ch, 1) != 1 ) {
            print STDERR "$0: Short read on input (file corrupt)\n";
            exit 1;
        }
        $ch = ord($ch);
        $nybble_buf = $ch >> 4;
        $n = $ch & 0xF;
    }
    return $n;
}

print "P6\n";
print "$xsize $ysize\n";
print "255\n";

for ( $y = 0 ; $y < $ysize ; $y++ ) {
    $x = 0;
    $last = 0;
    undef $nybble_buf;          # Nybble buffer starts clear on each line
    while ( $x < $xsize ) {
        $n = get_nybble();

        if ( $n != $last ) {
            print $color{$n};
            $last = $n;
            $x++;
        } else {
            $c = get_nybble();
            if ( $c == 0 ) {
                # Double-nybble run
                $c = get_nybble();
                $c += get_nybble() << 4;
                $c += 16;
            }
            # Truncate overlong runs
            $c = $xsize-$x if ( $c > $xsize-$x );
            # Output run
            print $color{$n} x $c;
            $x += $c;
        }
    }
}