Physically Accurate Lighting Simulation /Introduction

Physically Accurate Lighting Simulation in Computer Graphics Software

A.B. Khodulev, E.A. Kopylov

Contents Introduction Lightscape System Specter System Radiance System Scenes for Comparison Experimental Results Conclusion Acknowledgments

INTRODUCTION

In this paper we investigate capabilities for physically accurate global lighting simulation in several computer graphics systems. We compare the following systems:

Lightscape Visualization system (LVS), ver. 1.2.4 distributed by Lightscape Technologies Inc.
Specter system ver. 4.83.1 distributed by Integra, Inc.
Radiance ver. 2.5, a public system developed by G.Ward [War94].

It should be mentioned that we used restricted version of LVS distributed for educational institutions.

All these systems allow to do global lighting analysis but they use different approaches to solve the global light propagation equation ("rendering equation", [Kaj86]).

LVS uses radiosity method [CCWG88] for global light propagation simulation and backward ray tracing for rendering (image generation).

Specter uses bi-directional ray tracing with forward Monte Carlo ray tracing used for producing view-independent illuminance distribution in a model (the so called illumination maps) while in further invocations of backward ray tracing for creating high-quality view-dependent images information is retrieved from the illumination maps.

Radiance uses backward Monte Carlo ray tracing. It also stores illuminance distribution as a set of point samples (that is used instead of the Specter illumination maps).

As we are mainly interested in physical accuracy of the systems, the following criteria are used for comparison:

Comprehensiveness and physical correctness of scene description. This relates to types of light sources available in model and material attributes available. The latter correlate with range of physical mechanisms of light-material interaction that can be simulated (local reflectance model).
Completeness of a global light propagation model. A complete model assumes that all possible ways of light propagation are taken into account.
Accuracy of simulation and capabilities for user monitoring/controlling the accuracy. All systems provide some control over a trade-off among accuracy and processing time, i. e. the former may be improved at the expense of the latter; therefore, the accuracy criterion is tightly connected with the processing speed criterion.
We also take into account some user interface features such as interactive facilities and presentation of calculation results. While not related to physical accuracy these features contribute considerably in convenience of system usage.

Sections 1-3 below analyze each system from the viewpoint of the above criteria with the exception of simulation accuracy that was examined experimentally. Results of this experimental comparison are presented on "Scenes for Comparison" and "Experimental Results" pages.

Contents Introduction Lightscape System Specter System Radiance System Scenes for Comparison Experimental Results Conclusion Acknowledgments


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