image resizing in perl

perl is really versatile, and can do a lot of things. moreover, you can do it in a lot of different ways. the difficult part being sometimes to choose the way you want to do it...

so i need to resize an image within perl. this is for games::risk, a perl implementation of the famous board game (btw, try it and tell me if you like it!). i want the background image to fit the window size on resize events. of course, i want it to be fast - but i also want something maintainable.

looking on cpan, i found 3 modules: gd, image::magick and image::imlib2. using gd to resize a picture is a nightmare, therefore i ditched it for image::resize which is a convenient wrapper around gd.

here are the needed incantations to resize:

• with imlib2



my $old = Image::Imlib2->load($src);
my $new = $old->create_scaled_image($w, $h);



• with image::magick - note that the operation is done inplace, so one needs to clone the image first to compare the same things.
  



my $old = Image::Magick->new;
$old->Read($src);
my $new = $old->Clone;
$new->Scale(width=>$w, height=>$h);



• with image::resize



my $old = Image::Resize->new($src);
my $new = $old->resize($w, $h);

so i benchmarked them and found that on average, image::imlib2 is a few times faster than image::magick, which is itself around the same speed or a bit faster than image::resize.

however, image::imlib2 has a drawback: the only way to get back the new image is to save it to a file, where one can get the new image as a scalar directly:

• image::resize with $img->jpeg
• image::magick with $img->ImageToBlob
  

therefore, one must also take this into account in the benchmarking! so here's the latest version of the bench:

#!/usr/bin/perl

use 5.010;
use strict;
use warnings;

use Benchmark qw{ :all };
use Image::Size;                                                                                                                                             

use Image::Resize;
use Image::Imlib2;
use Image::Magick;

my $src = "src.jpg";
my $dst = "dst.jpg";

my ($w, $h) = imgsize($src);
my @sizes = (
 [10,10], [100,100], [1000,1000],
 [640,400], [840,600], [1024,768],
 [$w,$h], [$w/2,$h/2], [$w/4,$h/4],
 [$h,$w], [$h/2,$w/2], [$h/4,$w/4],
);

my $imlib2 = Image::Imlib2->load($src);
my $resize = Image::Resize->new($src);
my $magick = Image::Magick->new; $magick->Read($src);

foreach my $s ( @sizes ) {
 my ($width, $height) = @$s;
 say "-> ${width}x${height}";
 local $/;

 cmpthese( -3, {
     imlib2 => sub {
         my $img = $imlib2->create_scaled_image($width, $height);
         $img->save($dst);
         open my $fh, '<', $dst;
         return <$fh>;
     },
     magick => sub {
         my $img = $magick->Clone;
         $img->Scale(width=>$width,height=>$height);
         return $img->ImageToBlob;
     },
     resize => sub {
         my $img = $resize->resize($width,$height);
         return $img->jpeg; # $img->png
     },
 } );
 say '';
}

and i was quite astonished to see that image::imlib2 is still 2 or 3 times faster that image::magick or image::resize!

so, imlib2 may not the best api around, but sure it's fast...