[Bf-cycles] Velvet Shaders Sigma

Julian Herzog julian.hzg at gmail.com
Mon Aug 12 12:24:09 CEST 2013

Hi Greg,

I'm no expert on this topic, but a similar quesiton was answered here:
few days ago, if that helps.


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
> _______________________________________________
> Bf-cycles mailing list
> Bf-cycles at blender.org
> http://lists.blender.org/mailman/listinfo/bf-cycles
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.blender.org/pipermail/bf-cycles/attachments/20130812/6fc2436f/attachment.htm 

More information about the Bf-cycles mailing list