Authors
Robert L. Cook, Kenneth E Torrance
Cornell University; Lucasfilm Ltd.
Portals
Summary
This paper presents a reflectance model for rough surfaces. Given a light source, a surface, and an observer, a reflectance model describes the intensity and spectral composition of the reflected light reaching the observer. The intensity of the reflected light is determined by the intensity and size of the light source and by the reflecting ability and surface properties of the material. The spectral composition of the reflected light is determined by the spectral composition of the light source and the wavelength-selective reflection of the surface.
Abstract
A new reflectance model for rendering computer sythesized images is presented. The model accounts for the relative brightness of different materials and light sources in the same scene. It describes the directional distribution of the reflected light and a color shift that occurs as the reflectance changes with incidence angle. A method for obtaining the spectral energy distribution of the light relfected from an object made of a specific real material is presented, and a procedure for accurately reproducing the color associated with the spectral energy distribution is discussed. The model is applied to the simulation of a metal and a plastic.
Contribution
- The new reflectance model is applied to the simulation of a metal and a plastic, with an explanation of why images rendered with previous models often look plastic, and how this plastic appearance can be avoided
Overview
This paper presents a reflectance model for rough surfaces that is more general than previous models. It is based on geometrical optics and is applicable to a broad range of materials, surface conditions, and lighting situations. The basis of this model is a reflectance definition that relates the brightness of an object to the intensity and size of each light source that illuminates it. The model predicts the directional distribution and spectral composition of the reflected light. A procedure is described for calculating red, green, and blue (RGB) values from the spectral energy distribution.