Global Illumination

• physics-based illumination
• origins: heat transfer and illumination engineering
• diffuse reflection
• results are view independent
• object-space algorithm
• infinite reflections: energy balance
• soft shadows, colour bleeding, dark corners

Definitions

flux

energy per unit time (W)

 

radiosity, B

exiting flux density (W/m^2)

 

E

exiting flux density for lightt sources

 

reflectivity, R

fraction of incoming light which is reflected (unitless)

 

form factor, Fij

fraction of energy leaving Ai and arriving at Aj,

determined by geometry of polygons i and j

Energy balance

Matrix form of radiosity system

Problems

• matrix is O(n^2)
• form-factor computation costly
• computing visibility costly
• reconstruction of continuous image from constant radiosity patches
• curved surfaces?
• sharp shadows?
• refraction, translucency, specularity?

Partial Solutions

• use iterative methods
• compute form-factors on-demand
• progressive refinement: shoot from brightest emitters first
• create and use hierarchy
• use non-constant basis functions
• hybrid radiosity / ray-tracing techniques