source: bootcd/isolinux/syslinux-6.03/utils/ppmtolss16

#!/usr/bin/perl
## -----------------------------------------------------------------------
##
##   Copyright 2004-2008 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.
##
## -----------------------------------------------------------------------

##
## ppmtolss16
##
## Convert a PNM file with max 16 colors to a simple RLE-based format:
##
## uint32 0x1413f33d    ; magic (littleendian)
## uint16 xsize         ; littleendian
## uint16 ysize         ; littleendian
## 16 x uint8 r,g,b     ; color map, in 6-bit format (each byte is 0..63)
##
## Then, a sequence of nybbles:
##
## N    ... if N is != previous pixel, one pixel of color N
## ... otherwise run sequence follows ...
## M    ... if M > 0 then run length is M
## ... otherwise run sequence is encoded in two nybbles,
##     littleendian, +16
##
## The nybble sequences are on a per-row basis; runs may not extend
## across rows and odd-nybble rows are zero-padded.
##
## At the start of row, the "previous pixel" is assumed to be zero.
##
## Usage:
##
##      ppmtolss16 [#rrggbb=i ...] < input.ppm > output.rle
##
## Command line options of the form #rrggbb=i indicate that
## the color #rrggbb (hex) should be assigned index i (decimal)
##

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

$magic = 0x1413f33d;

# Get a token from the PPM header.  Ignore comments and leading
# and trailing whitespace, as is required by the spec.
# This routine eats exactly one character of trailing whitespace,
# unless it is a comment (in which case it eats the comment up
# to and including the end of line.)
sub get_token() {
    my($token, $ch);
    my($ch);

    do {
        $ch = getc(STDIN);
        return undef if ( !defined($ch) ); # EOF
        if ( $ch eq '#' ) {
            do {
                $ch = getc(STDIN);
                return undef if ( !defined($ch) );
            } while ( $ch ne "\n" );
        }
    } while ( $ch =~ /^[ \t\n\v\f\r]$/ );

    $token = $ch;
    while ( 1 ) {
        $ch = getc(STDIN);
        last if ( $ch =~ /^[ \t\n\v\f\r\#]$/ );
        $token .= $ch;
    }
    if ( $ch eq '#' ) {
        do {
            $ch = getc(STDIN);
        } while ( defined($ch) && $ch ne "\n" );
    }
    return $token;
}

# Get a token, and make sure it is numeric (and exists)
sub get_numeric_token() {
    my($token) = get_token();

    if ( $token !~ /^[0-9]+$/ ) {
        print STDERR "Format error on input\n";
        exit 1;
    }

    return $token + 0;
}

# Must be called before each pixel row is read
sub start_new_row() {
    $getrgb_leftover_bit_cnt = 0;
    $getrgb_leftover_bit_val = 0;
}

# Get a single RGB token depending on the PNM type
sub getrgb($) {
    my($form) = @_;
    my($rgb,$r,$g,$b);

    if ( $form == 6 ) {
        # Raw PPM, most common
        return undef unless ( read(STDIN,$rgb,3) == 3 );
        return unpack("CCC", $rgb);
    } elsif ( $form == 3 ) {
        # Plain PPM
        $r = get_numeric_token();
        $g = get_numeric_token();
        $b = get_numeric_token();
        return ($r,$g,$b);
    } elsif  ( $form == 5 ) {
        # Raw PGM
        return undef unless ( read(STDIN,$rgb,1) == 1 );
        $r = unpack("C", $rgb);
        return ($r,$r,$r);
    } elsif ( $form == 2 ) {
        # Plain PGM
        $r = get_numeric_token();
        return ($r,$r,$r);
    } elsif ( $form == 4 ) {
        # Raw PBM
        if ( !$getrgb_leftover_bit_cnt ) {
            return undef unless ( read(STDIN,$rgb,1) == 1 );
            $getrgb_leftover_bit_val = unpack("C", $rgb);
            $getrgb_leftover_bit_cnt = 8;
        }
        $r = ( $getrgb_leftover_bit_val & 0x80 ) ? 0x00 : 0xff;
        $getrgb_leftover_bit_val <<= 1;
        $getrgb_leftover_bit_cnt--;

        return ($r,$r,$r);
    } elsif ( $form == 1 ) {
        # Plain PBM
        my($ch);

        do {
            $ch = getc(STDIN);
            return undef if ( !defined($ch) );
            return (255,255,255) if ( $ch eq '0' ); # White
            return (0,0,0) if ( $ch eq '1'); # Black
            if ( $ch eq '#' ) {
                do {
                    $ch = getc(STDIN);
                    return undef if ( !defined($ch) );
                } while ( $ch ne "\n" );
            }
        } while ( $ch =~ /^[ \t\n\v\f\r]$/ );
        return undef;
    } else {
        die "Internal error: unknown format: $form\n";
    }
}

sub rgbconvert($$$$) {
    my($r,$g,$b,$maxmult) = @_;
    my($rgb);

    $r = int($r*$maxmult);
    $g = int($g*$maxmult);
    $b = int($b*$maxmult);
    $rgb = pack("CCC", $r, $g, $b);
    return $rgb;
}

foreach $arg ( @ARGV ) {
    if ( $arg =~ /^\#([0-9a-f])([0-9a-f])([0-9a-f])=([0-9]+)$/i ) {
        $r = hex($1) << 4;
        $g = hex($2) << 4;
        $b = hex($3) << 4;
        $i = $4 + 0;
    } elsif ( $arg =~ /^\#([0-9a-f]{2})([0-9a-f]{2})([0-9a-f]{2})=([0-9]+)$/i ) {
        $r = hex($1);
        $g = hex($2);
        $b = hex($3);
        $i = $4 + 0;
    } elsif ( $arg =~ /^\#([0-9a-f]{3})([0-9a-f]{3})([0-9a-f]{3})=([0-9]+)$/i ) {
        $r = hex($1) >> 4;
        $g = hex($2) >> 4;
        $b = hex($3) >> 4;
        $i = $4 + 0;
    } elsif ( $arg =~ /^\#([0-9a-f]{4})([0-9a-f]{4})([0-9a-f]{4})=([0-9]+)$/i ) {
        $r = hex($1) >> 8;
        $g = hex($2) >> 8;
        $b = hex($3) >> 8;
        $i = $4 + 0;
    } else {
        print STDERR "$0: Unknown argument: $arg\n";
        next;
    }

    if ( $i > 15 ) {
        print STDERR "$0: Color index out of range: $arg\n";
        next;
    }

    $rgb = rgbconvert($r, $g, $b, 64/256);

    if ( defined($index_forced{$i}) ) {
        print STDERR "$0: More than one color index $i\n";
        exit(1);
    }
    $index_forced{$i} = $rgb;
    $force_index{$rgb} = $i;
}

$form = get_token();
die "$0: stdin is not a PNM file" if ( $form !~ /^P([1-6])$/ );
$form = $1+0;

$xsize = get_numeric_token();
$ysize = get_numeric_token();
if ( $form == 1 || $form == 4 ) {
    $maxcol = 255;              # Internal convention
} else {
    $maxcol = get_numeric_token();
}
$maxmult = 64/($maxcol+1);      # Equal buckets conversion

@data = ();

for ( $y = 0 ; $y < $ysize ; $y++ ) {
    start_new_row();
    for ( $x = 0 ; $x < $xsize ; $x++ ) {
        die "$0: Premature EOF at ($x,$y) of ($xsize,$ysize)\n"
            if ( !scalar(@pnmrgb = getrgb($form)) );
        # Convert to 6-bit representation
        $rgb = rgbconvert($pnmrgb[0], $pnmrgb[1], $pnmrgb[2], $maxmult);
        $color_count{$rgb}++;
        push(@data, $rgb);
    }
}

# Sort list of colors according to freqency
@colors = sort { $color_count{$b} <=> $color_count{$a} } keys(%color_count);

# Now we have our pick of colors.  Sort according to intensity;
# this is more or less an ugly hack to cover for the fact that
# using PPM as input doesn't let the user set the color map,
# which the user really needs to be able to do.

sub by_intensity() {
    my($ra,$ga,$ba) = unpack("CCC", $a);
    my($rb,$gb,$bb) = unpack("CCC", $b);

    my($ia) = $ra*0.299 + $ga*0.587 + $ba*0.114;
    my($ib) = $rb*0.299 + $gb*0.587 + $bb*0.114;

    return ( $ia <=> $ib ) if ( $ia != $ib );

    # If same, sort based on RGB components,
    # with highest priority given to G, then R, then B.

    return ( $ga <=> $gb ) if ( $ga != $gb );
    return ( $ra <=> $rb ) if ( $ra != $rb );
    return ( $ba <=> $bb );
}

@icolors = sort by_intensity @colors;

# Insert forced colors into "final" array
@colors = (undef) x 16;
foreach $rgb ( keys(%force_index) ) {
    $i = $force_index{$rgb};
    $colors[$i] = $rgb;
    $color_index{$rgb} = $i;
}

undef %force_index;

# Insert remaining colors in the remaining slots,
# in luminosity-sorted order
$nix = 0;
while ( scalar(@icolors) ) {
    # Advance to the next free slot
    $nix++ while ( defined($colors[$nix]) && $nix < 16 );
    last if ( $nix >= 16 );
    $rgb = shift @icolors;
    if ( !defined($color_index{$rgb}) ) {
        $colors[$nix] = $rgb;
        $color_index{$rgb} = $nix;
    }
}

while ( scalar(@icolors) ) {
    $rgb = shift @icolors;
    $lost++ if ( !defined($color_index{$rgb}) );
}

if ( $lost ) {
    printf STDERR
        "$0: Warning: color palette truncated (%d colors ignored)\n", $lost;
}

undef @icolors;

# Output header
print pack("Vvv", $magic, $xsize, $ysize);

# Output color map
for ( $i = 0 ; $i < 16 ; $i++ ) {
    if ( defined($colors[$i]) ) {
        print $colors[$i];
    } else {
        # Padding for unused color entries
        print pack("CCC", 63*$i/15, 63*$i/15, 63*$i/15);
    }
}

sub output_nybble($) {
    my($ny) = @_;

    if ( !defined($ny) ) {
        if ( defined($nybble_tmp) ) {
            $ny = 0;            # Force the last byte out
        } else {
            return;
        }
    }

    $ny = $ny & 0x0F;

    if ( defined($nybble_tmp) ) {
        $ny = ($ny << 4) | $nybble_tmp;
        print chr($ny);
        $bytes++;
        undef $nybble_tmp;
    } else {
        $nybble_tmp = $ny;
    }
}

sub output_run($$$) {
    my($last,$this,$run) = @_;

    if ( $this != $last ) {
        output_nybble($this);
        $run--;
    }
    while ( $run ) {
        if ( $run >= 16 ) {
            output_nybble($this);
            output_nybble(0);
            if ( $run > 271 ) {
                $erun = 255;
                $run -= 271;
            } else {
                $erun = $run-16;
                $run = 0;
            }
            output_nybble($erun);
            output_nybble($erun >> 4);
        } else {
            output_nybble($this);
            output_nybble($run);
            $run = 0;
        }
    }
}

$bytes  = 0;
undef $nybble_tmp;

for ( $y = 0 ; $y < $ysize ; $y++ ) {
    $last = $prev = 0;
    $run = 0;
    for ( $x = 0 ; $x < $xsize ; $x++ ) {
        $rgb = shift(@data);
        $i   = $color_index{$rgb} + 0;
        if ( $i == $last ) {
            $run++;
        } else {
            output_run($prev, $last, $run);
            $prev = $last;
            $last = $i;
            $run  = 1;
        }
    }
    # Output final datum for row; we're always at least one pixel behind
    output_run($prev, $last, $run);
    output_nybble(undef);       # Flush row
}

$pixels = $xsize * $ysize;
$size = ($pixels+1)/2;
printf STDERR "%d pixels, %d bytes, (%2.2f%% compression)\n",
    $pixels, $bytes, 100*($size-$bytes)/$size;