Photon Mapping
Overview
Photon mapping is a global illumination method to calculate the contribution of indirect illumination during rendering. It simulates the way actual light disperses over a scene - from the light towards the eye - as opposed to regular ray tracing where the light rays are traced "backwards" - from the eye to the light source. It is capable of emulating both light concentrations from refracted light (caustics) and diffuse illumination from reflected light. It was developed by Henrik Wann Jensen.
The algorithm works by first running a pre-processing step where the contribution of each light is stored in a photon map. Then this information is used during regular ray tracing.
Algorithm
The photon map is generated by sending a swarm of light rays from each light into the scene. The light rays are reflected, refracted and attenuated by the objects in the scene. For each intersection, an entry about the lights direction and color (a "photon") is stored in the photon map.
Then during ray tracing, the surrounding area around each intersection is checked in the photon map to gather information about the indirect illumination contribution at the intersection point.
Links
Henrik Wann Jensen's
[1]Paper
[2]Book
--Jdj 14:52, 27 September 2006 (UTC)
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