The quantities everything else is defined in terms of.
Colour is the family; a dashed line is the second member of it.
Ratio of outgoing radiance to incoming irradiance for a pair of directions. The formalism that lets a material be specified independently of the tran… · 1965
States outgoing radiance at a point as emission plus the integral of incoming radiance weighted by the BSDF. Unified the previously separate ray trac… · 1986
A BRDF and a BTDF taken together, defined over the whole sphere rather than the upper hemisphere, so that one function describes both sides of a surf…
A surface may not reflect more energy than it receives. Violating it makes multi-bounce renders diverge into brightness rather than settle.
A physically valid BSDF gives the same value when incoming and outgoing directions are swapped. Bidirectional algorithms depend on it: without it, a…
The problem of computing how radiance moves through a scene from emitters to the camera, accounting for every path it can take on the way.
Power per unit projected area per unit solid angle. It is the quantity that is constant along a ray in a vacuum, which is why renderers transport it…
Light leaving a surface on the same side it arrived from.
Light crossing into a medium with a different index of refraction, bending by Snell's law and changing radiance by the squared IOR ratio.
Light redirected inside a medium rather than at a surface boundary.
Render a material under uniform unit illumination with no absorption. A conserving, non-absorbing BSDF disappears against the background; anything vi…