References
Ebert, Musgrave, Peachey, Perlin, Worley. Texturing & Modeling: A Procedural Approach (3rd Edition), Morgan Kaufmann Publishers, San Francisco, CA, 2002.
Lagae, Lefebvre, Cook, DeRose, Drettakis, Ebert, Lewis, Perlin Zwicker. State of the Art in Procedural Noise Functions, Eurographics, 2010.
Olano, Hart, Heidrich, Mark, Perlin, Real Time Shading Languages, SIGGRAPH 2002 Course 36, 2002.
http://www.nyu.edu/its/pubs/connect/archives/99fall/lewisimprov.html