Fast and Detailed Approximate Global Illumination with Irradiance Decomposition

Okan Arikan   - University of California, Berkeley
David Forsyth   - University of Illinois, Urbana-Champaign
James O'Brien   - University of California, Berkeley

Abstract

In this paper we present an approximate method for accelerated computation of the final gathering step in a global illumination algorithm. Our method operates by decomposing the radiance field close to surfaces into separate far- and near-field components that can be approximated individually. By computing surface shading using these approximations, instead of directly querying the global illumination solution, we have been able to obtain rendering time speed ups on the order of 10x compared to previous acceleration methods. Our approximation schemes rely mainly on the assumptions that radiance due to distant objects will exhibit low spatial and angular variation, and that the visibility between a surface and nearby surfaces can be reasonably predicted by simple location- and orientation-based heuristics. Motivated by these assumptions, our far-field scheme uses scattered-data interpolation with spherical harmonics to represent spatial and angular variation, and our near-field scheme employs an aggressively simple visibility heuristic. For our test scenes, the errors introduced when our assumptions fail do not result in visually objectionable artifacts or easily noticeable deviation from a ground-truth solution. We also discuss how our near-field approximation can be used with standard local illumination algorithms to produce significantly improved images at only negligible additional cost.

Download

Okan Arikan, David A. Forsyth, James O'Brien. Fast and Detailed Approximate Global Illumination with Irradiance Decomposition. ACM Transactions on Graphics (ACM SIGGRAPH 2005), pp 1108--1114, 2005.

Paper

Software

The source code for the algorithm we presented is available as a part of Pixie, hosted on http://pixie.sourceforge.net

High Res - High Dynamic Range (HDR) versions of the figures

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Figure 2
Irradiance Caching
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Spherical Harmonic 
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Final Image 
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Ground truth image
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Figure
Ground truth

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Our method

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Figure 4
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Figure 4 - insets
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SH sample locations

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SH sample locations

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SH sample locations

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Figure 6
Our method

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Irradiance caching

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Ground truth

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Figure 6 - insets
Our method
SH sample locations

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Irradiance caching
Sample locations

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Difference images
4 times magnified error
 image for our method

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4 times magnified error
image for irradiance 
caching

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Figure 7
Spot light + Bounce light

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Spot light + Bounce light
+ Local correction

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Figure 8

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