use strict;
use warnings;
use feature 'say';

use Imager;
use Image::PNG::Rewriter;

use IO::Compress::Deflate 'deflate', ':constants';
use Compress::Zopfli::ZLIB 'compress';

my $name = 'PNG_transparency_demonstration_1.png';
open my $fh, '<', $name;
binmode $fh;

Imager-> new( fh => $fh )
      -> write( type => 'png', data => \my $png_imager );

seek $fh, 0, 0;
my $rw = Image::PNG::Rewriter-> new( 
    handle => $fh, 
    zlib   => sub {
        my $input = shift;
        deflate \$input   => \my $output, 
                -Level    => 9, 
                -Strategy => Z_FILTERED;
        return $output
    }
);
$rw-> refilter( $rw-> original_filters );   # no-op
my $png_zlib9 = $rw-> as_png;

seek $fh, 0, 0;
$rw = Image::PNG::Rewriter-> new( 
    handle => $fh, 
    zlib   => \&compress,
);
$rw-> refilter( $rw-> original_filters );   # no-op
my $png_zopfli = $rw-> as_png;

my $f = "%-24s%s\n";
printf $f, 'Original file', -s $name;
printf $f, 'Re-saved with Imager',   length $png_imager;
printf $f, 'Compressed with zlib',   length $png_zlib9;
printf $f, 'Compressed with zopfli', length $png_zopfli;

__END__

Original file           179559
Re-saved with Imager    203632
Compressed with zlib    198642
Compressed with zopfli  179618