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Bidirectional Photon Mapping
Jiří VorbaCharles University in Prague
Faculty of Mathematics and Physics
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Motivation
Goal: Robust Global IlluminationPhoton Mapping good at:
CausticsReflections of causticsSmall light sources
Photon Mapping bad at:Glossy scenes
© H.W.Jensen
© Wojciech Jarosz
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Our contribution
Photon Mapping
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Outline
Review of Photon Mapping (Jensen et al.)Main ideaAlgorithm overviewResultsApplication to progressive methodsConclusion
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Photon Mapping review
First passPhoton shootingOverall lighting approximation
© Kavita Bala
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Photon Mapping review
Second passLight path connection heuristic
Primary rays
BRDF lobe
PMquery
Secondary rays
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PM issues
1. Correlated queries
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PM issues
2. Radiance estimate variance
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Main idea
PMquery
PMquery
PMquery
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1st strategy
PMquery
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2nd strategy
PMquery
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3rd strategy
PMquery
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Strategy combination
Multiple importance sampling (Veach 97)
321
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PPP
Pw
321
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PPP
Pw
321
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PPP
Pw
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Algorithm overview
First passthe same as in PM
Second passPath-TracingRadiance estimate at every path vertexlight path contribution multiplied by
MIS weight
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Results
Photon Mapping Our Bidirectional Photon Mapping
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Application to progressive methods (not a part of the CESCG article)
Overcoming the memory limitsSolving finer detailsConsistent method
Our implementationBased on Stochastic Progressive PM
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Progressive resultsOur progressive bidirectional method Our bidirectional method
(not progressive)
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Results
Photon Mapping Progressive Bidirectional Photon Mapping
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Reference - PT(320x320, 4 days on 6 cores)
PBDPM (512x512, 1 day 3h on 6 cores)
Results
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Limitation
Bias introduced by an inappropriate MIS weights “gap” between a photon hit and a camera ray end point
PMquery
PMquery
Our assumption
Reality
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Conclusion
ContributionNew more robust photon mapping based
method Future works
“Area light source” strategyCompensate the bias introduced by
inappropriate MIS weights
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The end
Thank you!Questions?
Reference - PT(320x320, 4 days on 6 cores)
PBDPM (512x512, 1 day 3h on 6 cores)