#! perl -slw
use strict;
use GD;

our $T ||= 150;

my $file = shift @ARGV;
die "$file not found" unless -e $file;

my $in = GD::Image->new( $file ) or die $!;
my( $w, $h ) = $in->getBounds;

## New palette image with just two colors
my $out = GD::Image->newPalette( $w, $h );
my $black = $out->colorAllocate( 0, 0, 0 );
my $white = $out->colorAllocate( 255, 255, 255 );

for my $y ( 0 .. $h - 1 ) {
    for my $x ( 0 .. $w -1 ) {
        my( $r, $g, $b ) = $in->rgb( $in->getPixel( $x, $y ) );
        ## Map the pixels relative to the threshhold 
        my $index = (( $r = $g +$b ) / 3) > $T ? $black : $white;
        $out->setPixel( $x, $y, $index );
    }
}

open OUT, '>:raw:perlio', "BW-$file" or die $!;
print OUT $out->png( 9 );
close OUT;

#system 1, "BW-$file"; ## display image