Precomputed Radiance Transfer (PRT) is a
computer graphics technique used to render a scene in real time with complex light interactions being precomputed to save time.
Radiosity methods can be used to determine the diffuse lighting of the scene, however PRT offers a method to dynamically change the lighting environment.
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In essence, PRT computes the illumination of a point as a linear combination of incident
irradiance In radiometry, irradiance is the radiant flux ''received'' by a ''surface'' per unit area. The SI unit of irradiance is the watt per square metre (W⋅m−2). The CGS unit erg per square centimetre per second (erg⋅cm−2⋅s−1) is often used ...
. An efficient method must be used to encode this data, such as
spherical harmonics.
When spherical harmonics are used to approximate the light transport function, only low-frequency effects can be handled with a reasonable number of parameters.
Ren Ng
Yi-Ren Ng (born September 21, 1979) is a Malaysian American scientist who is an assistant professor in the Department of Electrical Engineering & Computer Sciences at the University of California, Berkeley. He was the founder, executive chairman a ...
extended this work to handle higher frequency shadows by replacing spherical harmonics with non-linear
wavelets.
Teemu Mäki-Patola gives a clear introduction to the topic based on the work of
Peter-Pike Sloan et al. At
SIGGRAPH
SIGGRAPH (Special Interest Group on Computer Graphics and Interactive Techniques) is an annual conference on computer graphics (CG) organized by the ACM SIGGRAPH, starting in 1974. The main conference is held in North America; SIGGRAPH Asia ...
2005, a detailed course on PRT was given.
References
*Peter-Pike Sloan, Jan Kautz, and John Snyder. "Precomputed Radiance Transfer for
Real-time rendering in Dynamic, Low-Frequency Lighting Environments".
ACM Transactions on Graphics, Proceedings of the 29th Annual Conference on Computer Graphics and Interactive Techniques (SIGGRAPH), pp. 527-536. New York, NY: ACM Press, 2002
*NG, R., RAMAMOORTHI, R., AND HANRAHAN, P. 2003. All-Frequency Shadows Using Non-Linear Wavelet Lighting Approximation. ACM Transactions on Graphics 22, 3, 376–381
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3D computer graphics