Dagstuhl 2000 presentation

This is a HTML version of the slides from my presentation at the Dagstuhl seminar in June 2000. The presentation was an up-to-date version of my article "Faster photon map global illumination" in the Journal of Graphics Tools. Compared to that article, the render times have been significantly reduced, and I also talked about possible future improvements of the method.

Faster Photon Map Global Illumination

Per H. Christensen

Square USA, Honolulu, Hawaii

Abstract: The photon map method is an extension of ray tracing that enables it to efficiently compute caustics and soft indirect illumination on surfaces and in participating media. This presentation describes a method to further speed up the computation of soft indirect illumination on surfaces The speed-up is based on the observation that the many look-ups in the global photon map during final gathering can be simplified by (pre)computing local irradiance values at the photon positions. Our tests indicate that the calculation of soft indirect illumination can be sped up by a factor of 5-7 in typical scenes. The irradiance values can be computed before or during rendering. Other applications include participating media and importance at ``importon'' positions.


Advantages of the photon map method

The photon map method: overview

  1. Photon pass: emit, trace, store photons
  2. Sort photons
  3. Rendering: ray tracing with final gather and photon map lookups

1) Photon Pass

(figure showing photon paths in a Cornell box and the photons stored in the global map)

2) Sort photons

3) Rendering


Faster final gathering


Example: classic ray tracing

Classic ray tracing: 12 min. (soft shadows, textures)

Example: photon map

500,000 photons. Tracing: 39 sec, sorting: 12 sec

Example: irradiance (1)

(figure omitted -- see the JGT article)

Irradiance estimates at image sample points (200 photons)

Example: irradiance (2)

(figure omitted -- see the JGT article)

Precomputed irradiance estimates at 500,000 photon positions. Precomputation: 5 min. (Voronoi diagram)

Example: irradiance (3)

Precomputed irradiance estimates at 125,000 photon positions. Precomputation: 1.2 min.

Example: radiance

Radiance estimates (this is what the final gather "sees")

Example: complete image

Complete image. Final gathering: 69 min -> 13 min. Total render time: 94 min -> 28 min.


Other applications

Ideas for future work

Faster precomputation (1)

Faster precomputation (2)

No precomputation


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