The Lit Sphere: A Model for Capturing NPR Shading from Art
Author(s): Peter-Pike J. Sloan, William Martin, Amy A. Gooch, Bruce Gooch.
Proceedings: Graphics Interface (GI'01), June,
2001.
[BibTeX] 
Abstract:
While traditional graphics techniques provide for the realistic
display of three-dimensional objects, these methods
often lack the flexibility to emulate expressive effects
found in the works of artists such as Michelangelo and
Cezanne. We introduce a technique for capturing custom
artistic shading models from sampled art work. Our
goal is to allow users to easily generate shading models
which give the impression of light, depth, and material
properties as accomplished by artists. Our system
provides real-time feedback to immediately illustrate
aesthetic choices in shading model design, and to assist
the user in the exploration of novel viewpoints. We describe
rendering algorithms which are easily incorporated
into existing shaders, making non-photorealistic rendering
of materials such as skin, metal, or even painted objects
fast and simple. The flexibility of these methods
for generating shading models enables users to portray
a large range of materials as well as to capture the look
and feel of a work of art. (Color images can be found at
http://www.cs.utah.edu/npr/papers/LitSphere HTML.)