Further reading:

1. A semi-standard textbook on the subject, but now a bit dated (don't be fooled by the 2002 date on the 3rd ed., most of the text is from the 1st ed): http://www.amazon.com/Texturing-Modeling-Third-Edition-Proce...

2. A more recent but much shorter survey paper: http://graphics.tudelft.nl/Publications-new/2009/SDGTB09a/SD...

If you like this topic check out "Texturing and Modeling: a Procedural Approach" which covers Perlin noise and other similar algorithms. The books shows you how Pixar generates life like surfaces and effects in Renderman. http://www.amazon.com/Texturing-Modeling-Third-Procedural-Ap...