my @redmap = map {  int( $r * $_)  } 0..255;
my @greenmap = map {  int( $g * $_)  } 0..255;
my @bluemap = map {  int( $b * $_)  } 0..255;
[..]
 $newimg->map( red=>\@redmap, green=>\@greenmap, blue=>\@bluemap );

 $newimg->filter(type=>'contrast', intensity=> $c);

##</code><code>##

my @redmap = map {  int( $r + $_)  } 0..255;