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.
One-line summary: How to make photon map global illumination 5-7 times faster.
Published in: Journal of Graphics Tools, volume 4, number 3, pages 1-10. ACM, 1999.
Download paper here: jgt99.pdf.
High-resolution images and errata here: JGT page.
Reprinted, with corrections and comments, in: Ronen Barzel, editor. Graphics Tools: The JGT Editors' Choice, pages 241-251. A K Peters, 2005.
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