Faster Photon Map Global Illumination

Per H. Christensen

This paper appears in issue Volume 4, Number 3.
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Abstract

The photon map method is an extension of ray tracing that makes it able to efficiently compute caustics and soft indirect illumination on surfaces and in participating media. This paper describes a method to further speed up the computation of soft indirect illumination (diffuse-diffuse light transport such as color bleeding) 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 precomputing local irradiance values at the photon positions. Our tests indicate that the calculation of soft indirect illumination during rendering, which is the most time-consuming part, can be sped up by a factor of 5-7 in typical scenes at the expense of 1) a precomputation that takes about 2%-5% of the time saved during rendering and 2) a 28% increase of memory use.

Author Information

Per H. Christensen, Square USA, 55 Merchant Street #3100, Honolulu, HI 96813 per.christensen@acm.org

Figures

The following images are from the figures in the text. Click on any thumbnail to view the full image.

Figure 1. Cornell box with spheres

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(a) Global photon map.

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(b) Irradiance estimates computed at image sample points (dimmed for display).

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(c) Precomputed irradiance estimates at all 400,000 photon positions (dimmed for display).

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(d) Precomputed irradiance estimates at 100,000 photon positions (dimmed for display).

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(e) Radiance estimates based on (d).

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(f) Soft indirect illumination computed with final gathering.

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(g) Complete image with direct illumination, specular reflection and refraction, caustics, and soft indirect illumination.

Figure 2. Interior

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(a) Global photon map.

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(b) Irradiance estimates computed at image sample points (dimmed for display).

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(c) Precomputed irradiance estimates at all 500,000 photon positions (dimmed for display).

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(d) Radiance estimates based on (c).

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(e) Complete image with direct illumination, specular reflection, and soft indirect illumination.

Errata

  • The third sentence in section 3.2 of the printed text is garbled. It should read:
    (We chose not to store photons in a caustic photon map for this scene since caustics are an orthogonal issue to the method described here.)
  • The author list for reference [Christensen et al. 96] is incorrect in the printed text. The complete reference should read:
    Per H. Christensen, Eric J. Stollnitz, David H. Salesin, and Tony D. DeRose. “Global Illumination of Glossy Environments using Wavelets and Importance.” ACM Transactions on Graphics, 15(1): 37-71 (January 1996).
  • The author list for reference [Smits et al. 92] is incorrect in the printed text. The complete reference should read:
    Brian E. Smits, James R. Arvo, and David H. Salesin. “An Importance-driven Radiosity Algorithm.” Computer Graphics (Proc. SIGGRAPH 92) 26(2): 273-282 (July 1992).

BibTeX Entry

@article{Christensen99,
  author = "Per H. Christensen",
  title = "Faster Photon Map Global Illumination",
  journal = "journal of graphics tools",
  volume = "4",
  number = "3",
  pages = "1-10",
  year = "1999",
}