ABSTRACT
Radiance is the final quantity computed by the rendering process. So far, we have been using the reflectance equation to compute it:
Lo(p,v) =
∫ Ω
f(l,v)⊗ Li(p, l) cos θidωi, (9.1)
where Lo(p,v) is the outgoing radiance from the surface location p in the view direction v; Ω is the hemisphere of directions above p; f(l,v) is the BRDF evaluated for v and the current incoming direction l; Li(p, l) is the incoming radiance into p from l; ⊗ is the piecewise vector multiplication operator (used because both f(l,v) and Li(p, l) vary with wavelength, so are represented as RGB vectors); and θi is the angle between l and the surface normal n. The integration is over all possible l in Ω.
