I’ve submitted chapter 7 of jQuery 1.3 with PHP to Packt, which involves image manipulation. The editor I build in that chapter allows you to non-destructively manipulate an image in the most commonly needed ways – resize, rotate and crop.
The idea is that when you upload an image, it’s usually not yet right to include in a website. People tend to upload massive photos (3000×2000 or so) and resize it down using the
<img> attributes, which is the wrong way to do it (see here for a solution to that particular problem).
However, once you’ve resized an image down, you can’t change it back.
The solution is to make copies of the image with your manipulations applied to them. That lets you make multiple versions of the same image.
But again, there’s the problem that if you change your mind about the original image, you can replace that, but the others all need to be redone.
Yet another problem is that unless you’ve kept records, there’s no link from the new images back to the original, so if you need to make space on the server by removing files that might not be in use anymore, you can’t be certain what thumbnails are still relevant and what are not.
The solution is to not actually create copies, but to record the changes applied to the original image in the URL of your manipulated image. When the server is asked for those URLs, it runs the manipulations on the original image and gives you back the new image. Of course, we will cache the new manipulations so this doesn’t need to be done every time, but this now allows you to replace the original image, then clear the cache, forcing all the variants of it to refresh, without you needing to do it again.
What this means, is that when the manipulation is recorded in the URL, no new copy is actually created until some browser actually requests it. This means that you can periodically clear your old thumbnails, safe in the knowledge that if they were still relevant, they will be recreated from the archived originals automatically the next time they’re needed.
This is, as usual, just a demo. It’s not designed to be impressive, but just to show how to do manipulations.
A permanent URL is provided, in the same manner as google maps – it updates itself as you manipulate it. To see the actual cropped, resized and rotated image, try opening that permanent URL in a different tab.
The GUI here is a means to an end (the permanent URL). In your own CMS, you might force a certain width/height for uploaded images automatically using the URL for example.
The example image I manipulated in the chapter is the IMG_0134.JPG in chp7. Try rotating, resizing, and cropping (drag your mouse on the image).
Little thing to note about that URL – there’s no query indicator. Standards-compliant browsers treat the ‘?’ mark in a URL as an indication that the result should never be cached, but that would be pretty expensive for the server, so we remove that. The
get.php file rebuilds the query from the
$_SERVER['REQUEST_URI'] and sends out the manipulated image with caching headers.
The graphics manipulation was done using Imagick, which is a PECL extension that allows PHP to run ImageMagick functions internally.
In Fedora, you can install Imagick with
yum install php-pecl-imagick. In CentOS, follow these instructions.
CentOS users might have a problem with the latest Imagick (2.2.2), so change the
pecl install imagick line to
pecl install imagick-2.2.1.
Make sure to edit the
images_libs.php file to point to your own image repositories. The images don’t need to be in a web-accessible directory.