CMSC 635 Global Illumination

 Local Illumination  light – surface – eye  Throw everything else into ambient  Global Illumination  light – surface – surface … – eye  Multiple bounces  Local Illumination  light – surface – eye  Throw everything else into ambient  Global Illumination  light – surface – surface … – eye  Multiple bounces

Global Illumination ambient no ambient global illumination

“Backward” algorithms  Follow light transport: eye to light  Traditional ray tracing  Follow primary reflection  Path tracing  Follow other rays  Monte-carlo integration  Follow light transport: eye to light  Traditional ray tracing  Follow primary reflection  Path tracing  Follow other rays  Monte-carlo integration

“Forward” algorithms  Follow light transport: light to eye  Lights are emitters  Everything else both emitter & receiver  Integrate bounce to bounce  All surfaces for each bounce (radiosity)  All bounces for one photon (photon map)  Follow light transport: light to eye  Lights are emitters  Everything else both emitter & receiver  Integrate bounce to bounce  All surfaces for each bounce (radiosity)  All bounces for one photon (photon map)

Radiosity  Based on radiant heat transport  Diffuse surfaces only  Try to find steady state solution  Based on radiant heat transport  Diffuse surfaces only  Try to find steady state solution

Sample Locations  Usually need more samples than provided by geometric patches  Uniform subdivision  Adaptive regular subdivision  Adaptive irregular subdivision  Usually need more samples than provided by geometric patches  Uniform subdivision  Adaptive regular subdivision  Adaptive irregular subdivision

Discontinuity Meshing Lischinski, Tampieri and Greenburg, “Combining Hierarchical Radiosity and Discontinuity Meshing”, SIGGRAPH 93

Discontinuity Meshing Lischinski, Tampieri and Greenburg, “Combining Hierarchical Radiosity and Discontinuity Meshing”, SIGGRAPH 93

Interactive Rendering  Diffuse surfaces only  viewpoint independent  Pre-compute and store radiosity  As patch/vertex colors  As texture  Separate solution for each light  Linear combination to change lights  Diffuse surfaces only  viewpoint independent  Pre-compute and store radiosity  As patch/vertex colors  As texture  Separate solution for each light  Linear combination to change lights

Two pass  Radiosity for diffuse  Ray tracing for reflection  Doesn’t handle radiosity of specularly reflected light  Radiosity for diffuse  Ray tracing for reflection  Doesn’t handle radiosity of specularly reflected light

Radiometric Units TermSymbolUnits Radiant EnergyQJ Radiant Flux (Power)  = dQ/dt W = J/s Irradiance (entering) E = d  /dA W/m 2 Radiosity (exiting) B = d  /dA W/m 2 Radiant Intensity I = d  /d  W/sr Radiance L = d 2  /(d  dA) W/(sr m 2 )

Photometric Units TermSymbolUnits Luminous EnergyQtalbot Luminous Flux  = dQ/dt lm = talbot/s Illuminance (entering) E = d  /dA lx = lm/m 2 Luminous exitance m = d  /dA lm/m 2 Luminous Intensity I = d  /d  cd = lm/sr Luminance L = d 2  /(d  dA) lm/(sr m 2 )