A comment on this script was made to me thru email, and so I'll post it here in case in may help someone looking at this snippet.

edada wrote:

Hi, I had some problems changing brightness with Imager using your code :

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);
[download]

In Imager::Filters doc I can read that the contrast filter "scales each channel by intensity. Values of intensity < 1 will reduce the contrast". Your map do the same if $r => $b => $g ! It's supposed to change brightness and not contrast. I simply recommand you writing it with a :

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

and using null value as default value.