Editing Photon mapping (section)

{{short description|Two-pass global illumination rendering algorithm}}
In [[computer graphics]], '''photon mapping''' is a two-pass [[global illumination]] [[Rendering (computer graphics)|rendering]] [[algorithm]] developed by [[Henrik Wann Jensen]] between 1995 and 2001<ref>Jensen, H. (1996). ''Global Illumination using Photon Maps''. [online] Available at: http://graphics.stanford.edu/~henrik/papers/ewr7/egwr96.pdf</ref> that approximately solves the [[rendering equation]] for integrating [[radiance|light radiance]] at a given point in space. [[Ray tracing (graphics)|Rays]] from the light source (like [[photon]]s) and rays from the camera are traced independently until some termination criterion is met, then they are connected in a second step to produce a radiance value. The algorithm is used to realistically simulate the interaction of light with different types of objects (similar to other [[photorealistic rendering]] techniques). Specifically, it is capable of simulating the [[refraction of light]] through a [[Transparent material|transparent substance]] such as [[glass]] or [[water]] (including [[Caustic (optics)|caustics]]), [[diffuse interreflection]] between illuminated objects, the [[subsurface scattering]] of light in translucent materials, and some of the effects caused by [[particulate matter]] such as smoke or [[water vapor]].  Photon mapping can also be extended to more accurate simulations of light, such as [[spectral rendering]]. Progressive photon mapping (PPM) starts with ray tracing and then adds more and more photon mapping passes to provide a progressively more accurate render.

Unlike [[path tracing]], [[Path tracing#Bidirectional path tracing|bidirectional path tracing]], [[volumetric path tracing]], and [[Metropolis light transport]], photon mapping is a [[Unbiased rendering|"biased" rendering algorithm]], which means that averaging infinitely many renders of the same scene using this method does not converge to a correct solution to the [[rendering equation]].  However, it is a consistent method, and the accuracy of a render can be increased by increasing the number of photons. As the number of photons approaches infinity, a render will get closer and closer to the solution of the rendering equation.