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[Reusser <reu### [at] chorus net>]
| Sounds interesting, but what exactly is it (in terms of not what it
| does, but how it works)? Is it an extension on ray-tracing?
It can be implemented in any ray-tracer as described in the pdf-file.
| I caught that BRDF is bi-linear reflection diffusion function or
| something on that order, but what does that mean?
A BRDF function gives the reflectance of a target as a function of
illumination geometry and viewing geometry.
Not much help?
It's for modelling the reflection of materials where the viewing
direction and light direction will affect the look of of the material.
The classic example here is velvet. The reason why velvet looks like
it does is because it is in reality dozens of hairs standing up, which
means, among other things, that it will remain relatively dark when lit
slightly from behind, recause you're just illuminating the backside of
the hairs. Modelling the hairs is of course not practical, but this is
where the BRDF function comes in. You can think of it as regular ol' fake
bumpmapping, but on a much smaller scale.
BRDF-functions can be "captured" from real materials aswell, as
described in.
http://graphics.stanford.edu/~smr/cs348c/surveypaper.html
Okay. Enough about BRDF, and on to BSSRDF.
BRDF models pretty well how light scatters from a totally opaque surface,
but a lot of materials are slightly translucent, ie. milk, human skin,
marble, etc.
BSSRDF is an extension of BRDF that also takes into account subsurface
scattering, meaning light rays actaully penetrate the surface, bounce
around and lights up the object, and reflect some of the rays back.
The PDF contains a very convincing series of images of a glass of milk.
First modeled with a diffuse BRDF function, which basically looks like
a piece of white plastic, and then with BSSRDF as skimmed mink and
whole milk.
| (Not all of us are able to decode
| the pdf file and figure out what they are talking about.)
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