#!/usr/bin/perl

use strict;
use warnings;
use Imager;

my $gif = shift || die 'need an image';
my $img = Imager->new;

$img->read(file => $gif)
or die $img->errstr;

$img = $img->scale(scalefactor => 0.5);

$img->write(file => join '.', $gif, 'half', 'gif')
or die $img->errstr;