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OrenNayar reflectance model 88
Oren–Nayar reflectance model
The Oren-Nayar reflectance model, developed by Michael Oren and Shree K. Nayar, is a reflectance model for
diffuse reflection from rough surfaces. It has been shown to accurately predict the appearance of a wide range of
natural surfaces, such as concrete, plaster, sand, etc.
Introduction
Reflectance is a physical property of a material that
describes how it reflects incident light. The appearance
of various materials are determined to a large extent by
their reflectance properties. Most reflectance models
can be broadly classified into two categories: diffuse
and specular. In computer vision and computer
graphics, the diffuse component is often assumed to be
Lambertian. A surface that obeys Lambert's Law
appears equally bright from all viewing directions. This
model for diffuse reflection was proposed by Johann
Heinrich Lambert in 1760 and has been perhaps the
most widely used reflectance model in computer vision
Comparison of a matte vase with the rendering based on the
Lambertian model. Illumination is from the viewing direction
and graphics. For a large number of real-world surfaces, such as concrete, plaster, sand, etc., however, the
Lambertian model is an inadequate approximation of the diffuse component. This is primarily because the
Lambertian model does not take the roughness of the surface into account.
Rough surfaces can be modelled as a set of facets with different slopes, where each facet is a small planar patch.
Since photo receptors of the retina and pixels in a camera are both finite-area detectors, substantial macroscopic
(much larger than the wavelength of incident light) surface roughness is often projected onto a single detection
element, which in turn produces an aggregate brightness value over many facets. Whereas Lambert’s law may hold
well when observing a single planar facet, a collection of such facets with different orientations is guaranteed to
violate Lambert’s law. The primary reason for this is that the foreshortened facet areas will change for different
viewing directions, and thus the surface appearance will be view-dependent.