Precomputed Radiance Transfer
Encyclopedia
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.
In essence, PRT computes the illumination of a point as a linear combination of incident irradiance
. An efficient method must be used to encode this data, such as Spherical harmonic
s.
When spherical harmonics is used to approximate the light transport function, only low frequency effect can be handled with a reasonable number of parameters. Ren Ng extended this work to handle higher frequency shadows by replacing spherical harmonics with non-linear wavelet
s.
Teemu Mäki-Patola gives a clear introduction to the topic based on the work of Peter-Pike Sloan et al. At SIGGRAPH 2005, a detailed course on PRT was given.
Computer graphics
Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....
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.
In essence, PRT computes the illumination of a point as a linear combination of incident irradiance
Irradiance
Irradiance is the power of electromagnetic radiation per unit area incident on a surface. Radiant emittance or radiant exitance is the power per unit area radiated by a surface. The SI units for all of these quantities are watts per square meter , while the cgs units are ergs per square centimeter...
. An efficient method must be used to encode this data, such as Spherical harmonic
Spherical Harmonic
Spherical Harmonic is a science fiction novel from the Saga of the Skolian Empire by Catherine Asaro. It tells the story of Dyhianna Selei , the Ruby Pharaoh of the Skolian Imperialate, as she strives to reform her government and reunite her family in the aftermath of a devastating interstellar...
s.
When spherical harmonics is used to approximate the light transport function, only low frequency effect can be handled with a reasonable number of parameters. Ren Ng extended this work to handle higher frequency shadows by replacing spherical harmonics with non-linear wavelet
Wavelet
A wavelet is a wave-like oscillation with an amplitude that starts out at zero, increases, and then decreases back to zero. It can typically be visualized as a "brief oscillation" like one might see recorded by a seismograph or heart monitor. Generally, wavelets are purposefully crafted to have...
s.
Teemu Mäki-Patola gives a clear introduction to the topic based on the work of Peter-Pike Sloan et al. At SIGGRAPH 2005, a detailed course on PRT was given.