Am 17.06.2012 13:19, schrieb FlyerX:
> Hello,
>
> I am working with the SSLT features in RC5 (Windows 64bit) and so far
> they seem to give nice results and I am adding it to PoseRay as a
> material property.
>
> According to the POV-Ray documentation, there is additional information
> about the translucency for several materials listed in
> http://graphics.stanford.edu/papers/bssrdf/bssrdf.pdf.
>
> I suppose the documentation refers to Figure 5 in the SIGGRAPH
> publication. Which of the values (or combination of them) are we
> supposed to use? I was given by clipka a skin value of <2.0,1.5,0.8>
> which, according to him, should be between the skin1 and skin2 values in
> Figure 5 but does not seem to match the data.

The SSLT parameterization has been changed since its introduction, to 
allow for more intuitive tweaking, and also for easier use of patterned 
pigments.

The early implementation was parameterized by the "reduced scattering 
coefficient" (sigma-prime[s]) and the "absorption coefficient" 
(sigma[alpha]); as these two parameters completely define a material's 
apparent color, the materials regular pigment was ignored; finding 
suitable parameters for materials not listed in the paper was 
cumbersome, as the relation between the coefficients and the resulting 
color is far from intuitive. Furthermore, using image maps to e.g. add 
some variation to a skin texture would have been impossible with this 
approach.

The current implementation takes two different parameters, from which it 
then computes the aforementioned coefficients internally. These 
parameters are the material's "diffuse reflectance" (R[d]) - i.e. the 
resulting apparent color of the material, which is conveniently 
specified via the classic pigment statement (modulated by the diffuse 
parameter) - and the "mean free path" (the inverse of sigma[tr]) - which 
is what you specify via the "translucency" parameter.


This parameterization has been suggested by Jensen & Buhler in a 
follow-up paper, "A Rapid Hierarchical Rendering Technique for 
Translucent Materials", but they didn't compute the corresponding values 
for the materials listed in the earlier paper.

Of course, from the equations in the two papers a formula can be thrown 
together to compute the translucency parameter from the measured values, 
but so far I haven't found the time and patience.

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