$img->write( file => $outfile, type => 'png', compression => 0 );
$img->write( file => $outfile, type => 'png', compress => 0 );
$img->write( file => $outfile, type => 'png', level => 0 );
$img->write( file => $outfile, type => 'png', quality => 0 );
... I've tried these and many more, including every variation or combination I could think of