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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)