CMSC 635: Advanced Computer Graphics
Global Illumination

Spring 1999

Global Illumination

Global illumination must consider 4 types of light transport between pairs of surfaces.
1. diffuse to diffuse
2. specular to diffuse -- handles caustics and refraction
3. diffuse to specular
4. specular to specular
All must be considered at once for each light propagation path.
Post processing radiosity solution with ray-tracing won't work!

Why?
1. some specular may be result of earlier diffuse reflection.
2. some diffuse may be re-reflected specular
Radiosity does :
- diffuse to diffuse correctly
Ray tracing does:
- specular to specular correctly
- diffuse to specular empirically
- specular to diffuse can be added in by a 2 pass method:
  Pass1 -- backward trace light from source to environment.
  Pass2 -- normal tracing using illumination from Pass1.

Combining Ray Tracing and Radiosity -- Two pass method:

Pass1: Enhanced Radiosity - View Independent [Rushmerier 90]

Pass2: ``Enhanced Ray-Tracing'' -- View Dependent

specular-specular -- normal ray tracing
diffuse-specular:
- 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 intensities here.
- can do recursively
only handles special cases of specular transmission and specular-diffuse reflection.