Progressive Photon Mapping

최인창 (Inchang Choi)

KAIST (Korea Advanced Institute of Science and Technology)

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● can simulate specular and diffuse material

● Problems:● Caustics (LS+DE)● SDS paths (LSDSE)

Intro: MC based methods

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Intro: Photon Mapping

● Two pass algorithm● First pass: Photon Tracing● Second pass: Ray Tracing using the

photon maps

● Problem:● Scenes dominated by caustics->We don’t have infinite memory

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Intro:Progressive Photon Mapping

● An extension of Photon Mapping● Include SDS paths with arbitrary

accuracy without infinite memory

● Multi-pass algorithm● First Pass: Ray Tracing● Subsequent Passes: Photon Tracing

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Photon Mapping

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Photon Mapping:First Pass: Photon Tracing

● Shoot photons from the light source● -using MC technique and Russian Roulette● -store photons in K-d tree

●Position, incident direction, flux

● Manage two photon maps● Caustic map● Global photon map

Caustic mapphotons

Global mapphotons

From John C. Hart’s ppt

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● Trace rays ● Calculate illumination using two

photon maps

Photon Mapping:Second Pass: Ray Tracing

Use the nearest N photons to estimate L at point x

A = r2

From John C. Hart’s ppt

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Photon Mapping:Second Pass: Ray Tracing

Direct Illumination

Diffuse Indirect Illumination

Specular Illumination

CausticIllumination

From Michael Kaiser and Christian Finger’s ppt

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● 1. Make the number of photons very large● (lim n->∞)● Use an Iterative method

● 2. Reduce the radius r● (limt r-> 0)● Reduce the radius every iteration

How can it be improved?

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Progressive Photon Mapping

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Progressive Photon MappingFirst Pass: Ray Tracing

● Shoot a ray from eye to the scene● Trace the path until the first non-

specular surface● Store the hit point if the surface has

non-specular(diffuse) component in the BRDF

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Progressive Photon MappingFirst Pass: Ray Tracing

● A Hit Point Structure

These are updated each subsequent passes

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● In each Pass● Trace a given number of photons into the

scene

Progressive Photon MappingSubsequent Pass: Photon Tracing

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● After each Pass● Loop all hit points

●:Find the photons within the radius●:refine the estimate of the illumination●(Reduce R, increase N, update τ)

Progressive Photon MappingSubsequent Pass: Photon Tracing

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Progressive Photon MappingRadius Reduction

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Progressive Photon MappingFlux Correction

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Progressive Photon MappingRadiance Evaluation

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A Video Result

● http://www.youtube.com/watch?v=zg9NcCw53iA

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Result Comparison

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Thank you for listening

● Any Questions?