Could this be added to POV-Ray?

http://graphics.stanford.edu/~henrik/papers/bssrdf/

The pdf-file on that page is pretty informative.


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> 
> Could this be added to POV-Ray?
> 
> http://graphics.stanford.edu/~henrik/papers/bssrdf/
> 
> The pdf-file on that page is pretty informative.

If they'd just include the girl in the models library, I'd be happy
enough.

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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?  I caught
that BRDF is bi-linear reflection diffusion function or something on
that order, but what does that mean?  (Not all of us are able to decode
the pdf file and figure out what they are talking about.)

 - Rico

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[Reusser <reu### [at] chorusnet>]
| 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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On Mon, 20 Aug 2001 19:33:58 -0500, Reusser <reu### [at] chorusnet>
wrote:

>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?  I caught
>that BRDF is bi-linear reflection diffusion function or something on
>that order, but what does that mean?  (Not all of us are able to decode
>the pdf file and figure out what they are talking about.)

If you're talking about BDRF, it means Bi-directional Reflectance
Function. This is a geeky way to say 'material reflectance
properties'. The bi- in the name suggests that it can be used for
anisotropic shading, for example brushed aluminum.

diffuse, specular, phong and even ambient are BDRFs, as is blinn.
There are many different BDRF models aimed at representing different
material properties. Some are very mterial-specific, for example silk,
hair, skin etc.

IIRC programmable shaders a la RenderMan allow for custom BDRFs, which
is a really powerful material creation tool.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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