Transcript Global Illumination

CMSC 635
Global Illumination
Global Illumination
 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
“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)
Radiosity
 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
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
Two pass
 Radiosity for diffuse
 Ray tracing for reflection
 Doesn’t handle radiosity of specularly
reflected light
Radiometric Units
Term
Radiant Energy
Symbol
Q
Units
J
Radiant Flux (Power)  = dQ/dt
W = J/s
Irradiance (entering)
Radiosity (exiting)
Radiant Intensity
E = d/dA
B = d/dA
I = d/d
W/m2
W/m2
W/sr
Radiance
L = d2/(d dA) W/(sr m2)
Photometric Units
Term
Luminous Energy
Symbol
Q
Units
talbot
Luminous Flux
 = dQ/dt
lm = talbot/s
Illuminance (entering) E = d/dA
Luminous exitance
m = d/dA
Luminous Intensity
I = d/d
Luminance
lx = lm/m2
lm/m2
cd = lm/sr
L = d2/(d dA) lm/(sr m2)