[Bf-cycles] Velvet Shaders Sigma

[Julian Herzog]

Hi Greg,

I'm no expert on this topic, but a similar quesiton was answered here:
http://blender.stackexchange.com/questions/2211/how-exactly-does-the-sigma-parameter-affect-the-velvet-shader/2212#2212
a
few days ago, if that helps.

Cheers,
Julian


2013/8/12 Greg Zaal <gregzzmail at gmail.com>

> Hey guys,
>
> I'm curious about the implementation of the Velvet shader - I can see that
> it only reflects light at grazing angles and that the Sigma value is a sort
> of IOR of some fresnel calculation, but how is it different from simply
> connecting fresnel/facing ratio to a diffuse shader?
>
> Why the name "Sigma" and not something a little more artist-friendly? Do
> other renderers use the same term?
>
> With only a single light source, there's a big black patch near the
> 0-degree grazing angle, facing directly at camera - is it possible to
> control the size of this big black patch or is it a fixed constant due to
> the concept of a velvet shader?
>
> But really I'd just like to know why this shader exists - what it's
> intended use is and why we can't just create the same effect using other
> shaders and some fresnel/light vector calculations.
>
> The wiki for the Sigma value is empty, so I'll update it with anything you
> can tell me.
>
> Cheers,
> Greg
>
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