[Bf-cycles] Velvet Shaders Sigma
gregzzmail at gmail.com
Mon Aug 12 16:49:03 CEST 2013
That makes sense, thanks Brecht.
On 12 August 2013 16:18, Brecht Van Lommel <brechtvanlommel at pandora.be>wrote:
> It could indeed use a better name, I don't know what other renderers
> call it. It's sigma as in the the variance of the normal distribution,
> controlling the sharpness of the peak. It's a kind of roughness I
> Velvet is made up of small threads along the normal of the surface,
> which means if you look straight at the surface there is no light
> reflected, only when viewing them from the side do you get light
> reflection. In practice threads aren't quite placed perfectly and
> there's also scattering going on between them, so this idealized model
> isn't enough and you would usually mix it with a diffuse shader.
> There is no light vector available for shading nodes so you couldn't
> do these calculations there.
> On Mon, Aug 12, 2013 at 11:06 AM, Greg Zaal <gregzzmail at gmail.com> wrote:
> > Hey guys,
> > I'm curious about the implementation of the Velvet shader - I can see
> > it only reflects light at grazing angles and that the Sigma value is a
> > 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
> > 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
> > use is and why we can't just create the same effect using other shaders
> > some fresnel/light vector calculations.
> > The wiki for the Sigma value is empty, so I'll update it with anything
> > can tell me.
> > Cheers,
> > Greg
> > _______________________________________________
> > Bf-cycles mailing list
> > Bf-cycles at blender.org
> > http://lists.blender.org/mailman/listinfo/bf-cycles
> Bf-cycles mailing list
> Bf-cycles at blender.org
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Bf-cycles