Exaggerated Shading for Depicting Shape and Detail
Author(s): Szymon Rusinkiewicz, Michael Burns, Doug DeCarlo.
Article: ACM Transactions on Graphics (Proc. SIGGRAPH'06), Vol. 25, No. 3, pp. 1199--1205, July,
2006.
[BibTeX] [DOI] 
Abstract:
In fields ranging from technical illustration to mapmaking, artists have developed distinctive visual styles designed to convey both detail and overall shape as clearly as possible. We investigate a non-photorealistic shading model, inspired by techniques for cartographic terrain relief, based on dynamically adjusting the effective light position for different areas of the surface. It reveals detail regardless of surface orientation and, by operating at multiple scales, is designed to convey detail at all frequencies simultaneously.