Introduction to Radiosity
Geometry Group Discussion Session
Jiajian (John) Chen
9/10/2007
Outline
•
•
•
•
•
Global Illumination and Radiosity
Overview of Radiosity Algorithms
How to Solve Radiosity Equations
Pros and Cons
References
Global Illumination and Radiosity
• Global illumination
– Add light intensity to 3D scene, including direct
illumination and indirect illumination (reflect,
refract)
– Algorithms: ray tracing, radiosity, ambient
occlusion, photon mapping, image based lighting,
…
– Radiosity was introduced into computer graphics
as a rendering method in 1984. (Initially it’s used
to solve radiative heat transfer problem)
Overview of Radiosity Algorithms
• Preprocess: Divide 3D scene into a group of
surfaces.
• Assumptions:
– Each surface can reflect light energy diffusely
(Lambert’s Law). Colorful reflected light will lead
to color bleeding on surfaces
– Each surface emits and reflects energy uniformly
over its whole area
•The equation is applied to each surface
•Need to compute each color component (RGB) by this equation
•Fij-s are computed between each pair of surfaces. Purely decided by
geometry between two surfaces. Expensive to calculate
How to Solve the Radiosity Equation
• “Full matrix” algorithm
Given Fij, pj, Ei, Solve Bi. Bi is the radiosity (intensity for coloring) for each
surface.
Expensive to get all N*N Fij and then compute the inversion of N*N matrix.
How to Solve the Radiosity Equation
• “Progressive” algorithm
•Compute Fij between surface i
and all other surfaces and
update the radiosity values for
all surfaces.
•It doesn't need to compute
N*N Fij, hence It lowers the
computation cost.
•Finally it gives the same result
as the “full matrix” algorithm
Pros and Cons
• Pros:
– Realistic lighting effects: shadow, reflection, …
– Independent of viewpoint
• Cons:
– Preprocess (divide environment into polygons)
– Large storage and computation cost
– Non-diffuse components not counted
References
• Radiosity and derived algorithms:
http://www.siggraph.org/education/materials
/HyperGraph/radiosity/
• Wiki:
http://en.wikipedia.org/wiki/Radiosity
• "Modeling the interaction of light between
diffuse surfaces", C. Goral, K. E. Torrance, D. P.
Greenberg and B. Battaile, Computer Graphics,
Vol. 18, No. 3.