Archive for April, 2011
There are two quantities flying around when writing a physically based renderer:
- Irradiance, which is power per unit area
- Radiance, which is power per unit area per unit projected solid angle
Any BSDF is the ratio between the two: a patch receives unit irradiance from some incident direction, the BSDF defines the radiance emitted for each outgoing direction.
At no point is (non-projected) solid angle used as a measure for the patch in question, yet many references and implementations consider probability density relative to this measure. In this post I will argue that using projected solid angle directly is more natural.