Beginning PHP 5.3

Chapter 17. Generating Images with PHP

The ability to create HTML pages dynamically using PHP lets you do some pretty clever stuff, as you've seen in previous chapters. However, there are some tasks that HTML isn't suited for, such as displaying graphical information. Furthermore, because images are commonly used on the Web, there's often a need to manipulate image files — for example, to resize them or add text to them.

Fortunately, PHP contains a range of functions that enable you to create, open, manipulate, and output images — both to the Web browser and to disk. In the course of this chapter you see how these functions work and how you can use them to create dynamic graphics for your pages. In this chapter you:

• Explore some of the basic concepts that you need to understand before you create images, such as color theory and how image coordinate systems work in PHP

• Learn to use PHP's drawing tools to build your own images from scratch, drawing lines, curves, and other shapes on your images

• See how to work with existing images, such as applying watermarks to images, creating thumbnails, and adding text

The image functions that PHP uses are based on the GD image library that is developed by Tom Boutell (www.boutell.com). The code for the GD library is bundled with the PHP installation and includes some enhancements to the original code. With the version of GD included in PHP you can do things like draw lines, ellipses, and rectangles; fill areas of an image; create text within images; ...