Hello,
I'm using the following snippet I found on perlmonks and have tried altering the code to transform a title image I have from color to black and white with the text being all black and the background being all white. I've had success doing this but when I save the file it still saves it using 256 colors.

Is there anyway to allocate just black and white before saving it to decrease the file size?

The code snippet is below: 

use warnings;
use strict;
use GD;

my $file = $ARGV[0];
chomp $file;

convert_to_bw($file);

sub convert_to_bw {

    my $in_file = shift;
    my $image = GD::Image->new("$in_file");

    unlink $in_file;
    my $ni_file = $in_file;

    my $i = 0;
    my $t = $image->colorsTotal();

    while($i < $t) {
    my( @c ) = $image->rgb( $i );
    
    # Convert the color image to black and white
    my $g = ( $c[0] + $c[1] + $c[2] ) / 3;

    $image->colorDeallocate($i);
    $image->colorAllocate( $g, $g, $g );

    my( @d ) = $image->rgb( $i );

    # Replace the background color with white 
    if ($d[0] > 150) {
        $image->colorDeallocate($i);
        $image->colorAllocate( 255, 255, 255 );
    }

    my( @e ) = $image->rgb( $i );

    # Replace the text with black 
    if ($e[0] > 10 && $e[0] < 255) {
        $image->colorDeallocate($i);
        $image->colorAllocate( 0, 0, 0 );
    }
        
    $i++;
    }

    my $colorsTotal = $image->colorsTotal();
    print "COLOR TOTAL: $colorsTotal\n";

    write_file( $ni_file, $image->png(9) );
}

sub write_file {
    
    my $i = shift;
    open DISPLAY, ">$i" or warn "can't clobber $i $!";
    binmode DISPLAY;
    print DISPLAY @_;
    close DISPLAY;
}

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In reply to GD - Two colors? by Anonymous Monk

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