It basically involves the use of PHP's image creation capabilities. The reference guide is here:
The process is quite simple...
- Create a new image with imagecreate() and get a handle to the image (the canvas)
- Create a colour palette with imagecolorallocate()
...and then plot individual pixels, shapes, text, lines etc. etc. onto the canvas to create whatever effect you want...
- Get the image stream with imagepng() (for a .png)
- Send the output of imagepng() to client
You can even have a PHP script as the src='' attribute of an <img> tag. For example:
The first line of tabletop.php is then something like:
header ("Content-type: image/png");
The output is then a .png that can form the top of a table with nice anti-aliased smooth corners.
Using this technique, you can easily experiment with different colour schemes without having to go into Photoshop every time. I only actually do this on my development server. When i'm happy with a colour scheme I run a script to go through all my "dynamic" img src's and convert them to actual .png files for publishing.
Hope this helps!