Bidirectional Importance Sampling for Unstructured Direct Illumination.

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Bibliographic Details
Title:	Bidirectional Importance Sampling for Unstructured Direct Illumination.
Authors:	Wang, Rui¹, Åkerlund, Oskar²
Source:	Computer Graphics Forum. Apr2009, Vol. 28 Issue 2, p269-278. 10p. 5 Color Photographs, 2 Diagrams, 1 Chart.
Subjects:	Lighting software, Computer graphics software, Ray tracing algorithms, Computer graphics research, Three-dimensional imaging, Photorealism, Statistical sampling software, Computer software
Abstract:	Recent research in bidirectional importance sampling has focused primarily on structured illumination sources such as distant environment maps, while unstructured illumination has received little attention. In this paper, we present a method for bidirectional importance sampling of unstructured illumination, allowing us to use the same method for sampling both distant as well as local/indirect sources. Building upon recent work in [ WFA*05 ], we model complex illumination as a large set of point lights. The subsequent sampling process draws samples only from this point set. We start by constructing a piecewise constant approximation for the lighting using an illumination cut [ CPWAP08 ]. We show that this cut can be used directly for illumination importance sampling. We then use BRDF importance sampling followed by sample counting to update the cut, resulting in a bidirectional distribution that closely approximates the product of the illumination and BRDF. Drawing visibility samples from this new distribution significantly reduces the sampling variance. As a main advance over previous work, our method allows for unstructured sources, including arbitrary local direct lighting and one-bounce of indirect lighting. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

Description
Abstract:	Recent research in bidirectional importance sampling has focused primarily on structured illumination sources such as distant environment maps, while unstructured illumination has received little attention. In this paper, we present a method for bidirectional importance sampling of unstructured illumination, allowing us to use the same method for sampling both distant as well as local/indirect sources. Building upon recent work in [ WFA*05 ], we model complex illumination as a large set of point lights. The subsequent sampling process draws samples only from this point set. We start by constructing a piecewise constant approximation for the lighting using an illumination cut [ CPWAP08 ]. We show that this cut can be used directly for illumination importance sampling. We then use BRDF importance sampling followed by sample counting to update the cut, resulting in a bidirectional distribution that closely approximates the product of the illumination and BRDF. Drawing visibility samples from this new distribution significantly reduces the sampling variance. As a main advance over previous work, our method allows for unstructured sources, including arbitrary local direct lighting and one-bounce of indirect lighting. [ABSTRACT FROM AUTHOR]
ISSN:	01677055
DOI:	10.1111/j.1467-8659.2009.01366.x