use strict;
use warnings;
# unused ... use feature 'say';
# unnecessary? ... use open IO => ':raw';
use GD;
use Convert::Color; # Handy..  Didn't know of this module

my $saturation_factor = 0.9;  # Will ultimately be coming from elsewhere

# ----

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

# ----

# this is as clear as mud in a beer bottle to me...
# my $gd = GD::Image-> newFromPngData( scalar qx/convert rose: png:-/, 1 );

my $gd = GD::Image->newFromPng("ruddy.png", 1) || die("cant on loading file\n"); # 1 = truecolour

# my ($max_X, $max_Y) = $gd->getBounds();  # My version
my $max_X = $gd->width;                    # TMTOWTDI
my $max_Y = $gd->height;

#for my $y ( 0 .. $gd->height - 1 ) {      # Construct causes 'unknown method' errors ()...
#    for my $x ( 0 .. $gd->width - 1 ) {
	
for my $y ( 0 .. $max_Y - 1 ) {
    for my $x ( 0 .. $max_X - 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, '>', 'new.png' or die;
binmode $fh;
print $fh $gd->png;
close $fh;