How To Create and Apply Image Filters in PHP

Most likely, the first time you heard about image filters was when you had to edit your vacation pictures to remove the "red eye" effect or an undesirable face. For such basic purposes, a little practice and some specialized software such as Adobe Photoshop or Paint Shop Pro is sufficient to end up with great pictures. But if you want to go beyond the basics you need to understand what a picture actually is, what the main algorithms dedicated to image processing are, and how a programming language, as PHP per example, can help you. Images are wonderfully malleable, and after you understand those points, you can develop your own custom image filters with PHP. This article covers:

• Introduction to the GD library, which provides PHP support for image processing
• Creating custom image filters by modifying pixel colors
• Implementing the "convolution" technique
• Creating custom image filters by modifying pixel positions