batch rgb brightness and contrast adjustment

Hi, sometimes you have a whole bunch of rgb files which are just too dark or light, and you want to adjust them all in one step. Well, I used to launch gimp and adjust each one individually, but that is a pain if you have more than a few files. Well here is a way with Imager.

The idea is very simple. You increase(decrease) the rgb values to adjust brightness, and you adjust the contrast with +- intensity.

Experiment on 1 first to get the best setting, then run it in a whole dir full of images. If you keep the $r $g $b values identical, the brightness change will be uniform, otherwise you will be adjusting "tint" as well.

#!/usr/bin/perl
use warnings;
use strict;
use Imager;
use File::Basename;

# Usage: "scriptname red blue green contrast"
# example: " script 2.0 2.0 0.5 2.0" 
# 1.0 is "no change", values less than 1 reduce 

my ($r,$g,$b,$c) = @ARGV;

$r = $r || 1;
$g = $g || 1;
$b = $b || 1;
$c = $c || 1;

umask 0022;
my @pics= <*.jpg *.gif *.png>;
my @exts = qw(.jpg .gif .png);

my $img = Imager->new();

my @redmap = map {  int( $r * $_)  } 0..255;
my @greenmap = map {  int( $g * $_)  } 0..255;
my @bluemap = map {  int( $b * $_)  } 0..255;

foreach my $file (@pics){
    my ($basename,$path,$suffix) = fileparse($file,@exts);
    $img->open(file=>$file) or die $img->errstr();

    my $newimg = $img->copy();
    $newimg->map( red=>\@redmap, green=>\@greenmap, blue=>\@bluemap );
    $newimg->filter(type=>'contrast', intensity=> $c);
    $newimg->write(file=>"$basename-b$suffix" );
}
[download]

Comment on batch rgb brightness and contrast adjustment Download Code

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Re: batch rgb brightness and contrast adjustment by zentara (Cardinal) on Oct 10, 2005 at 17:55 UTC
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. I'm not really a human, but I play one on earth. flash japh	[reply] [d/l] [select]

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Re: batch rgb brightness and contrast adjustment
by zentara (Cardinal) on Oct 10, 2005 at 17:55 UTC

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]

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

I'm not really a human, but I play one on earth. flash japh

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