Mr schrieb:
>> That may be due to the coefficients you picked for the material ;)
>>     
>
> Yes I got through so much trial and error because I didn't find examples nor any
> data on real world "sigmas" I must also confess, I din't understand what
> 1/mm as the way to express these coefficients meant. I hope I'm not bohering you
> guys by giving noob feedback on still undocumented beta.
>
>   
The original Jensen et al. paper has actual values for some materials - 
see Figure 5 (b) on page 5:

http://graphics.stanford.edu/papers/bssrdf/bssrdf.pdf

The sigma[a] coefficients basically specify how much absorption a light 
ray of a given wavelength suffers, per mm travelled in the medium (hence 
the 1/mm dimension; that's "odometer" distance btw, not simply |A-B|); 
the sigma-prime[s] coefficients specify how many scattering events a 
light ray of a given wavelength suffers on average (again per mm 
travelled in the medium), multiplied by a correctional factor to account 
for non-isotropic scattering.

These coefficients are admittedly hard to use and non-intuitive, as it 
is difficult to predict the resulting apparent material color, so I 
expect future versions to add another layer to automatically compute 
fitting coefficients, based on a user-specified apparent material color 
and some other RGB parameter to control the "waxiness" of the material 
(probably the "mean free path", which should be intuitive enough for 
this purpose).

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