use strict;
use warnings;
use feature 'say';
use open IO => ':raw';
use GD;
use Convert::Color;

sub desaturate {
    local $" = ',';
    my @HSV = Convert::Color-> new( "rgb8:@_" )-> as_hsv-> hsv;
    $HSV[ 1 ] *= 0.7;
    return Convert::Color-> new( "hsv:@HSV" )-> as_rgb8-> rgb8
}

my $gd = GD::Image-> newFromPngData( scalar qx/convert rose: png:-/, 1 );

for my $y ( 0 .. $gd-> height - 1 ) {
    for my $x ( 0 .. $gd-> width - 1 ) {
        my $packed_rgb = $gd-> getPixel( $x, $y );
        my @RGB = reverse unpack 'C3', pack 'L', $packed_rgb;
        $packed_rgb = unpack 'L', pack 'C3x', reverse desaturate( @RGB );
        $gd-> setPixel( $x, $y, $packed_rgb )
    }
}

open my $fh, '>', 'desaturated_rose.png' or die;
binmode $fh;
print $fh $gd-> png;
close $fh;