Photon Mapping and Irradiance Caching

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Photon Mapping and Irradiance Caching
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Bidirectional Paths
Light path
Eye path
Shadow ray
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Bidirectional Paths
flux (photons)
radiance
shadow ray
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Weighting the paths
Pixel estimate is weighted sum of path radiances
where
Choice of weights is critical for low
variance see Veach for details
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Advantages and disadvantages

• Bidirectional path tracing
• Good for small sources of strong indirect
  illumination (caustics)
• Path tracing
• Good for outdoor scenes with only a small part of
  the model visible
• Both have trouble sampling mirror images of
  caustics
• Both need lots of samples to avoid objectionable
  high frequency noise

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Photon mapping

• Cache light paths for efficiency?
• Decouple geometry and illumination
• Dont use illumination maps where number of
  samples needed is dependent on primitive size and
  scene complexity
• Get rid of high-frequency noise efficiently
• Density estimation
• However, density estimation produces biased (but
  consistent) samples

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Two pass approach

• Pass one photon tracing
• Build the photon map data structure
• Pass two rendering
• Trace eye paths using photon map to produce
  radiance estimates efficiently

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