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

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

my $i = Imager-> new( 

# defaults are RGB, 8 bits per channel

    xsize      => 256, 
    ysize      => 2,
    filetype   => 'raw',
    interleave => 1,            # RRRR...GGGG...BBBB...
    data       => \( pack 'C*', 
        ( 0 .. 255 ) x 3,       # 1st scanline is gradient
        ( 0 ) x ( 3 * 256 )),   # 2nd scanline is flat black
) or die;
$i-> write( data => \my $png, type => 'png' );

open my $fh, '<', \$png;
my $re = Image::PNG::Rewriter-> new( handle => $fh );

say for $re-> original_filters;

__END__

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