Reflection from Layered Surfaces due to Subsurface Scattering

Abstract:

The reflection of light from most materials consists of two major
terms: the specular and the diffuse. Specular reflection may be
modeled from first principles by considering a rough surface
consisting of perfect reflectors, or micro-facets. Diffuse reflection
is generally considered to result from subsurface scattering; that is,
light enters a surface layer, is scattered multiple times, and then
exits in a random direction in the process inheriting the color of the
surface. Accounting for diffuse reflection by Lambert's cosine law,
as is universally done in computer graphics, is not a physical theory
based on first principles.
This paper presents a model for subsurface scattering in layered
surfaces in terms of one-dimensional linear transport theory. The
solutions to this equation account for diffuse reflection from first
principles. This model is particularly appropriate for common layered
materials appearing in nature, such as biological tissues (e.g. skin,
leaves, etc.) or inorganic materials (e.g. snow, sand, paint,
varnished or dusty surfaces). As an application of the model, we
simulate the appearance of a face and a cluster of leaves, from
experimental data describing their layer properties.