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Acceleration of Monte Carlo Path Tracing in General Environments

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Use the 'best' samples to evaluate an integral: Probability ... SIMULGEN ESPRIT project #35772. http://iiia.udg.es/Simulgen. Generalitat de Catalunya's AIRE ... – PowerPoint PPT presentation

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Title: Acceleration of Monte Carlo Path Tracing in General Environments


1
Acceleration of Monte Carlo Path Tracing in
General Environments
Frederic Pérez1 Ignacio Martín1 François X.
Sillion2 Xavier Pueyo1
2
Outline
  • Importance Sampling
  • Previous work
  • Link Probabilities
  • Results
  • Conclusions
  • Future Work

3
Importance Sampling
  • Variance reduction technique
  • Use the best samples to evaluate an integral
    Probability Density Function (PDF) prop. to
    kernel
  • Reflectance equation
  • Importance sampling
  • Use of approximate for PDF ?
    Usually by means of a 1st pass

4
Previous Work
  • Chen et al. 91
  • Progressive Multi-Pass
  • Jensen 95
  • Importance Driven Photon Maps
  • Szirmay-Kalos et al. 98
  • Importance Driven Quasi-Random walk
  • Stürzlinger 96, Ureña Torres 97
  • Final Gathering

5
Shortcomings
  • Fixed subdivision of hemisphere
  • Cannot adapt to irradiance changes
  • Missing samples
  • Sources does not fit solid angles
  • Fixed subdivision of object space first pass

6
Link Probabilities Overview
  • 1st Pass Radiance Clustering
  • Produces Line-Space hierarchy Links
  • Coarse solution not for rendering
  • 2nd Pass Monte Carlo Path Tracing
  • Improved Importance Sampling with Link
    Probabilities
  • Use links arriving at leaves as a representation
    of the irradiance

7
Link Probabilities
  • Importance Sampling in a random walk step

for each bounce at point x
x
8
Link Probabilities PDF per leaf?
  • Using a PDF per leaf ? Artifacts for 1st
    bounce

? Solution Recompute PDF per pixel
9
Link Probabilities
  • Link overlap

S2
S1
y
? Check if links sender is hit
10
Link Probabilities
  • PDF accuracy and visibility

S1
l1
S2
l2
R
Finite elements pass ? two links arriving at
leaf R
11
Link Probabilities
  • PDF accuracy and visibility

Solution Adaptive PDFs
12
Results
  • Simple test scene

13
Results
  • Room with indirect illumination

14
Results
16 samples
128 samples
64 samples
NEE
806s
1613s
201s
LP
1273s
2434s
409s
15
Conclusions
  • Enhancement of Path Tracing by Importance
    Sampling based on the estimated irradiances
    computed with a Radiance Clustering 1st pass
  • Quality of the images doesnt strongly depend on
    the lighting conditions

16
Future Work
  • Extension for isotropic participating media
  • Account for links arriving to leaf clusters with
    media and sample directions as for surfaces
  • Addition of glossy surfaces and anisotropic
    participating media
  • Account for BRDF/phase function
  • Use of Link Probabilities in BPT
  • Eye paths as presented
  • Light paths similarly using importance
  • Comparison to Metropolis Light transport

17
Acknowledgments
  • SIMULGEN ESPRIT project 35772
  • http//iiia.udg.es/Simulgen
  • Generalitat de Catalunyas AIRE
  • CICYTs TIC98-0586-C03-02
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