1. CS 655 – Computer Graphics
Global Illumination

2. BRDF Measurments
FYI: Cornell has done BRDF measurements and made them available at:

3. Global Illumination
How do we accurately simulate all light interactions between objects?
Diffuse to Diffuse
Specular to Diffuse
Diffuse to Specular
Specular to Specular
Which are handled by Ray tracing? Which by Radiosity?

4. Global Illumination An accurate method must handle all four types
Radiosity – very good at diffuse-diffuse.
A two pass algorithm can include specular to diffuse.
Radiosity is view independent, specularity is not.
Ray tracing – specular to specular handled well.
Diffuse to specular handled somewhat.
Specular to diffuse can be included using a two-pass method or by backwards ray tracing.

5. Global Illumination
Putting light interactions in regular expression form, with
E = eye
L = light
D = Diffuse reflection or transmission
G = Glossy reflection or transmission
S = Specular reflection or refraction
How well do the various algorithms do?
Appel ray casting
Whitted recursive ray tracing
Kajiya path tracing
Goral radiosity:
E(D|G)L
E[S*](D|G)L
E[(D|G|S)+(D|G)]L
ED*L

6. Combining Rendering Algorithms
Can we get the diffuse interactions of radiosity and also the specular interactions of ray-tracing?
Several approaches to doing this
Each of them use two passes

7. Combining Radiosity and Ray Tracing
A two pass approach
Pass 1: enhanced radiosity to account for diffuse to diffuse and specular to diffuse.
Pass 2: diffuse to specular and specular to specular using enhanced ray tracing.
Why two passes?
A view-independent diffuse computation followed by a view-dependent specular computation is doable.