Wavelet Radiative Transfer and Surface Interaction
Robert R. Lewis
Imager Computer Graphics Lab
University of British Columbia
Department of Computer Science
20 February, 1996
Illumination is the study of how light interacts with matter to produce visible scenes. In computer graphics, we use illumination to produce realistic" images.
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.
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. Global illumination solutions are built on top of local illumination solutions.
In this paper, we will advance a new approach to an illumination solution that is intermediate between local and global illumination. Using wavelets, we are able to treat the interaction between two surfaces and the interaction of a surface with a radiation field in a source-to-destination model that applies to whole surfaces, not just small elements. We are continuing work to extend this to a fully global solution.
Wavelets are relatively recent additions to the rendering toolkit. They were first used by Gortler et al. [gort93] to solve the radiosity equations. Schr?oder et al. [schr93] and Christensen et al. [chri94] applied them to non-diffuse situations. What we present here may be considered a further development of that work.
Figure 1: Geometry
2 Radiative Transfer
and Surface Interaction
Let us first discuss some of the basics of how light is represented. The fundamental quantity is radiance, the amount of power passing in a given direction though a given surface per unit area (perpendicular to the direction of travel) per unit solid angle1.
1In this report, we will take radiance to be monochromatic and assume we can construct a polychromatic images by combining independently computed monochromatic images. We