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Light-Driven Global Illumination with a Wavelet Representation of
Light Transport
Robert R. Lewis
Alain Fournier
Imager Computer Graphics Laboratory
Department of Computer Science
University of British Columbia
31 March, 1995
Abstract
We describe the basis of the work he have currently under way to implement a new rendering algorithm called light-driven global illumination. This algorithm is a departure from conventional raytracing and radiosity renderers which addresses a number of deficiencies intrinsic to those approaches.
1 Introduction
Illumination is the study of how light interacts with matter to produce visible scenes. In computer graphics, we use illumination to produce realistic" images. Illumination studies both local" and global" phenomena.
Local illumination describes the interaction of light with a single, small volume or surface element with given incident and viewing directions. Figure 1 shows the typical geometry and and nomenclature for local illumination studies. The symbols are defined in Table 1. We have attempted to be compatible with the ANSI/IES standard [ans86] wherever possible.
The fundamental equation describing local illumina-
tion is
L = Le +
Z
?RN
fr(S0; V)Li jN ? S0j d!0i
+
Z
?TN
ft(S0; V)Li jN ? S0j d!0i (1)
where L is the total radiance given off (either Lr or Lt), Le is the surface emissivity, Li is the incident radiance, ?RN is the reflection hemisphere (contains V), ?TN is the transmission hemisphere (opposite ?RN), fr is the bidirectional reflectance distribution function (BRDF), ft is the bidirectional transmittance distribution function (BTDF), and d!i is sin ?id?idOEi. We use the to indicate bound variables of integration. A local illumination solution is entirely characterized by its BRDF and BTDF functions.
Global illumination describes how light is distributed in a scene: a collection of objects, including light sources, immersed in a given medium. Global illumination solutions must consider multiple reflections. The solution scope of global illumination may vary. We may be interested in determining illumination at a few points (e.g. the amount of light reaching reading surfaces in the design of an office), on visible surfaces (the viewer-dependent" solution), on all surfaces (the viewer-independent" solution), or