Using ImageMagick and GD2 together with Drupal ImageCache

A lot of Drupal sites use ImageCache and ImageAPI to automatically scale and process images for display. Most of them (the vast majority, unless I miss my guess) will be using the GD toolkit and running with mod_php embedded in Apache. This is fine in most cases, but sometimes it's definitely the wrong thing to do; in my case, I'm processing large image files (~4M or so) and keeping my memory limit down. The easiest way to do this is to offload the processing to another process. Something like ImageMagick perhaps? With a custom action from ImageCache Actions, this is simple!

A quick Google led me to an article called Create PDF thumbnails with imagecache and ImageMagick while GD is still the default toolkit which supplies the following code (simplified a little by removing the PDF-y bits):

<?php
$w = 246; // change to your preferred thumbnail width
if (!_imageapi_imagemagick_convert($image->source.'[0]', $image->source.'.png', array(0 => '-thumbnail '.$w))) return FALSE;
$img = imagecreatefrompng($image->source.'.png');
file_delete($image->source.'.png');
$image->resource = $img;
$image->toolkit = 'imageapi_gd';
$image->info = array('extension' => 'jpeg');
return TRUE;
?>

Alas, this code it pretty useless: because it stomps on $image->info any further actions on this $image will probably break.

Thankfully, there's an easy fix: when you update $image, make sure you update everything that needs fixing. Here's the amended code:

<?php
// "Thumbnail" the image
$width = 600;
if (!_imageapi_imagemagick_convert($image->source, $image->source.'.png', array(0 => '-thumbnail '.$width))) return FALSE;

// Load it back in as a GD resource
$img = imagecreatefrompng($image->source.'.png');

// Get the "deets" on the new image
$info = getimagesize($image->source.'.png');
$image->resource = $img;
$image->toolkit = 'imageapi_gd';
$image->info = array(
  'width' => $info[0],
  'height' => $info[1],
  'extension' => 'png',
  'file_size' => filesize($image->source.'.png'),
  'mime_type' => $info['mime'],
);

// Clean up
file_delete($image->source.'.png');

return $image;
?>

Make sure that you've enabled the ImageMagick toolkit, drop this code in a custom action and you'll be on externally processing images in no time!