precomputed local radiance transfer for real-time lighting design anders wang kristensen tomas...
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Precomputed Local Radiance Transfer for Real-time Lighting Design
Anders Wang KristensenTomas Akenine-Moller
Henrik Wann JensenSIGGRAPH ‘05
Presented by Shao-Ti Lee
2010/04/08
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OutlineIntroductionRelated WorkConstructing the Light CloudCompressing Surface RadianceReal-time RelightingResultsConclusion
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IntroductionRelated WorkConstructing the Light CloudCompressing Surface RadianceReal-time RelightingResultsConclusion
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IntroductionMAIN IDEA
◦Unstructured light cloud.
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IntroductionMAIN IDEA
◦Unstructured light cloud.
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IntroductionFEATURES
◦Local, not distant illumination. Accurately represent incident radiance on
different parts of the model.
◦Light positions and intensities are changeable.
◦Lights can be added or removed.◦Materials can be glossy.◦Camera is fully dynamic.◦Scene is assumed to be static.
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IntroductionRelated WorkConstructing the Light CloudCompressing Surface RadianceReal-time RelightingResultsConclusion
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Related WorkPrecompute the exitant radiance
[Wood et al. 2000; Chen et al. 2002]◦Basis: sphere harmonics.
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Related WorkSphere harmonics.
ApproximatedExitantRadiance
ApproximatedExitant Radiancein the SH basis
SH Basis
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Related WorkClustered PCA(Principle
Component Analysis) [Sloan et al. 2003]◦For geometry data representation
compression. ClusteringEx. K-Means
PCA
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IntroductionRelated WorkConstructing the Light CloudCompressing Surface RadianceReal-time RelightingResultsConclusion
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Constructing the Light Cloud
Before doing this, first divide the geometry into a set of discrete zones using a simple top-down partitioning algorithm.
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Constructing the Light Cloud
Use a two-stage approach to construct the light cloud.◦Stage 1 Make a sufficiently dense
uniform sampling of the region of interest.
◦Stage 2 The light cloud is then simplified by clustering similar lights using a bottom-up clustering algorithm.
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Constructing the Light Cloud
This is for point lights.
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Constructing the Light Cloud
This is for diffuse surface.
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Constructing the Light Cloud
A C
D E F
G H I A B C D E F G H I
Cluster List
Priority queue sorted by △jk
△AB △AD △BD △CE …..
S
S
Compute △SC , △SD , △SE , △SF , △SG ,△SH , △SI and re-sort the priority queue to end a loop and stop until △jk ≧1 for all j, k
B
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IntroductionRelated WorkConstructing the Light CloudCompressing Surface RadianceReal-time RelightingResultsConclusion
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Compressing Surface Radiance
Before compression◦Per vertex matrix X , with np = nb x
nl elements per color channel. nb : The number of SH bases.
nl : The number of lights.
After compression using CPCA
ClusterMean
PCA vectors(bases)
weights
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IntroductionRelated WorkConstructing the Light CloudCompressing Surface RadianceReal-time RelightingResultsConclusion
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Real-time RelightingOrganize the local lights in a kd-
tree and locate the m nearest lights.
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Real-time RelightingTo avoid undesirable popping
effects, set the weight for each pre-computed local light to
After computing all weights, normalization is used. And all weights are multiplied by the power of the light at l.
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Real-time RelightingVisibility problem
Solution: Use ray tracing with a few rays.
Cannot assign weights!
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Real-time RelightingDiscontinuity Problem
Suddenly disappear/appeardue to occlusion!
Solution:Smoothly fade out/in lights over time, but that now have become obscured by geometry.
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Real-time RelightingComputing Exitant Radiance
For each cluster, xm and bi are constant.
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Real-time RelightingReconstruct the vector of SH
coefficients representing exitant radiance in a vertex program by evaluating
◦Where is the variable to ensure that we get correct blending at the borders between clusters and between zones.
◦Recall that
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IntroductionRelated WorkConstructing the Light CloudCompressing Surface RadianceReal-time RelightingResultsConclusion
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Results
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Results
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Results
Left: Method of authors.Right: Ray tracing with per pixel lighting.
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Results
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IntroductionRelated WorkConstructing the Light CloudCompressing Surface RadianceReal-time RelightingResultsConclusion
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ConclusionThe system handles indirect
illumination efficiently for models with more than 100,000 triangles.
Future Work◦Soft shadow◦Spotlight