CMSC 635: Advanced Computer Graphics
David S. Ebert
Computer Science and Electrical Engineering Department
University of Maryland, Baltimore County
- Global illumination must consider 4 types of light
transport between pairs of surfaces.
- diffuse to diffuse
- specular to diffuse -- handles caustics and refraction
- diffuse to specular
- specular to specular
- All must be considered at once for each light propagation
- Post processing radiosity solution with ray-tracing won't
- some specular may be result of earlier diffuse reflection.
- some diffuse may be re-reflected specular
- Radiosity does :
- diffuse to diffuse correctly
- Ray tracing does:
Combining Ray Tracing and Radiosity -- Two
- Pass1: Enhanced Radiosity - View
Independent [Rushmerier 90]
- diffuse - diffuse
- General Equation
* - The last two items are only for specular surfaces that can't
see each other.
- Pass2: ``Enhanced Ray-Tracing'' -- View
- specular-specular -- normal ray tracing
- Integrate light arriving at reflection point by using a
square pyramid in the direction of specular bump.
- Divide into grid and do a z-buffer at low resolution to
see what is visible -- use radiosity calculated
- can do recursively
- only handles special cases of specular transmission and
Rendering Equation [Kajiya 1986]
- I(x,x') = transport intensity (from x' to x)
- g(x,x') = visibility between x and x'
- = transfer
emittance from x' to x.
- = scattering or bidirectional
reflectivity -- intensity of light at x' from
x''scattered in direction x.
- s means all points on all surfaces in the scene.
transport from x' to x = sum of light
emitted from x' in direction of x plus the total light
scattered from x' to x from all other surfaces.
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Last modified: Wed Mar 3 15:16:44 EST 1999