
A TwoPass Realistic Image Synthesis Method for
Complex Scenes
Kurt Zimmerman and Peter Shirley
Department of Computer Science
Indiana University
Bloomington, IN 47405
Program of Computer Graphics
Cornell University
Ithaca, NY 14853
Abstract
This paper presents a survey of twopass global illumination algorithms that use a local
pass (gather) and shadow ray optimization techniques as well as a new twopass algorithm
which relies on spatial coherence to efficiently handle the problem of numerous
luminaires. The algorithm presented operates on scenes with Lambertian reflectors and
luminaires with arbitrary emission distributions. A radiosity prepass is performed on a
simplified version of the scene. Bright reflecting surfaces are reclassified as light sources.
A spatial data structure is then built that associates bright visible surfaces to regions in
the environment. The visibility of these surfaces is probabilistically estimated. Finally,
a viewdependent gather" is performed at each pixel. This gather is made significantly
more efficient than previous algorithms because of careful integration based on the contents
of the spatial data structure.
CR Categories and Subject Descriptors: I.3.0 [Computer Graphics]: General;
I.3.6 [Computer Graphics]: Methodology and Techniques.
Additional Key Words and Phrases: Radiosity, realistic image synthesis, global
illumination, Monte Carlo Integration.
1 Introduction
In 1986 Kajiya introduced the rendering equation[8] and with it introduced an algorithm that, given sufficient computing time, can accurately solve all rendering problems that assume geometric optics. This has led to some speculation that global illumination is a solved problem[4]. However, a sufficient amount of computing time for Kajiya's algorithm is not practical for most rendering applications. Thus, since the introduction of Kajiya's algorithm, the goal of global illumination community has been a simple one: develop algorithms which can render realistic images to some accuracy goal in a practical amount of time. While there have been successful algorithms for simple scenes, most of these algorithms do not scale well when the environment becomes complex. So in spite of the volume of literature devoted to realistic rendering, a general and practical algorithm for producing physically accurate images of complex environments does not exist.