Non-Linear Approximation of Reflectance Functions

Eric P.F. Lafortune, Sing-Choong Foo, Kenneth E. Torrance, and Donald P. Greenberg

SIGGRAPH 97 Conference Proceedings, Los Angeles, California (August 1997), pp. 117-126.

We introduce a new class of primitive functions with non-linear parameters for representing light reflectance functions. The functions are reciprocal, energy-conserving and expressive. They can capture important phenomena such as off-specular reflection, increasing reflectance and retro-reflection. We demonstrate this by fitting sums of primitive functions to a physically-based model and to actual measurements. The resulting representation is simple, compact and uniform. It can be applied efficiently in analytical and Monte Carlo computations.

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