  Computer vision applications have heavily relied on the linear combination of
Lambertian diffuse and microfacet specular reflection models for representing
reflected radiance, which turns out to be physically incompatible and limited
in applicability. In this paper, we derive a novel analytical reflectance
model, which we refer to as Fresnel Microfacet BRDF model, that is physically
accurate and generalizes to various real-world surfaces. Our key idea is to
model the Fresnel reflection and transmission of the surface microgeometry with
a collection of oriented mirror facets, both for body and surface reflections.
We carefully derive the Fresnel reflection and transmission for each microfacet
as well as the light transport between them in the subsurface. This
physically-grounded modeling also allows us to express the polarimetric
behavior of reflected light in addition to its radiometric behavior. That is,
FMBRDF unifies not only body and surface reflections but also light reflection
in radiometry and polarization and represents them in a single model.
Experimental results demonstrate its effectiveness in accuracy, expressive
power, and image-based estimation.
