Something about skin shading...

#1

I have read an article that mention ppl in Weta also use LaFortune for Gollum skin shader. What is LaFortune ? Is it a kind of shading method like phong , Lambert.,etc?
Where can I get more info about it? And what is 3/4 specular calls? Is that mean the specular calculation will be executed 3 / 4 times?

 From [http://www.rendermanacademy.com/docs/SSS_depthmaps.htm](http://www.rendermanacademy.com/docs/SSS_depthmaps.htm)
 “It's a pretty good method (subsurface scattering using depthmaps). It's how Ken McGaugh and I wrote the Gollum skin shader. My advice is don't get too caught up in the science of it. Play around until you get the *look* that you want. Gollum had a subsurface term mixed with a straight lambertian term and 4 specular terms, one of which was a LaFortune which is essentially 3 specular calls. The biggest problems you'll run into are noise, we were doing 64-128 samples per shading call, and the fact that in using the shadowmap method, the brightness of your subsurface term is linked to some arbitrary trace depth, which wasn't a deal breaker, but it was a pain in the butt.”
#2

There is RenderMan shader code for this here:

http://www.graphics.cornell.edu/~westin/lafortune/lafortune.html

It is basically 3 phong specular calls which you can control using 18 coefficients. These coefficients can be determined from real measurements.

Simon

#3

you mean Lafortune is basically 3 phong specular calls?

do 3 phong specular calls have exactly same parameter(specualr value.,etc)? and the final result of 3 specular calls = result1 * result2 * result 3?

any example pic of their difference?

#4

No. Each specular call has a different “roughness” value for each vector component for each colour component. (I got it wrong its 27 coefficients). It’s basically a generic formular which can give you lots of different looks. The shader makes more sense - I’ve probably not explained it properly anyway.

There are a couple of images here http://www.graphics.cornell.edu/online/measurements/reflectance/skin/

Simon

#5

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