Global Illumination
[Angel p605-609; Foley p793-806]
- 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