1. Computer Graphics (Spring 2003)
COMS 4160, Lecture 23: Radiosity Ravi Ramamoorthi

2. Radiosity
Cornell box [Goral et al 84]

3. Rendering Equation

4. Radiosity Finite Element Method Assume Lambertian (polygonal) surfaces
View Independent
Classically, capture diffuse interreflection
Issues
Meshing (division into small elements)
Form Factors (Radiosity Matrix)
Solving Linear equations (Efficient iterative solution)

5. Earliest Radiosity pictures
Radiosity was first developed in other fields
Heat transport, Lighting Design
In graphics:
Goral et al. 84
Parry Moon and Domina Spencer
(MIT), Lighting Design, 1948

6. Radiosity Equation Simplest case: Assume surfaces are diffuse
Drop angular dependence, f is a constant
Discretize in constant elements
Matrix Equation, MB = E, with M = I-PF
Solve with iterative numerical techniques

7. Form Factors Defn of Form Factor Intuition
Bounce energy around until it’s absorbed
Like ray tracing except view-independent diffuse
Form factor controls fraction of energy from i to j

8. Nusselt’s Method

9. Hemicube

10. Hemicubes
Each small hemicube cell has a precomputed delta form factor:
We can render the scene using normal Z-buffer scan conversion onto the faces of the hemicube!

11. Monte Carlo Ray Tracing
Can be used to find form factors (slow)
Can be used directly to shoot energy

12. Solution Gathering Shooting Progressive Refinement Examples (plates)
Constructivist Museum: Chen, Feldman, Dorsey, Cornell 88