Following up his previous post on the subject, Pierre has post number two about some of the new features that GD in 5.1.x has.

With the png compression, I also forgot the couple of filters added in php5 some months ago. Like any additions after php 5.0, they have been added to the HEAD, which happens to 5.1.x now. The convolution I presented yesterday is one of them.

A simple list of the current filters: negate, grayscale, brightness, contrast, colorize, edgedetect (convolution), emboss (convolution), gaussian blur (convolution), selective blur, mean removal (convolution), smooth (convolution).

He also includes some samples of what can be done with each filter on a variety of subjects...