clipka <ano### [at] anonymousorg> wrote:
> Am 01.09.2016 um 16:06 schrieb Mr:
>
> >>> -Minnaert?
> >>
> >> Nope. Again, to the contrary: Minnaert also makes the diffuse component
> >> fall off at shallower angles.
> >
> > Blender's implementation can also do the opposite: lightening faces as their
> > normals get perpendicular to the viewing direction, kind of like oren Nayer also
> > does , but orders of magnitude stronger.  (" if Dark is 1 you get exactly the
> > Lambertian result. Higher darkness values will darken the center of an object
> > (where it points towards the viewer). Lower darkness values will lighten the
> > edges of the object, making it look somewhat velvet")
>
> I must confess that I'm digging into the Minnaert model only just now.
> And yes, it seems indeed to be capable of doing something like the
> Oren-Nayar and Lommel-Seeliger models.
>
> > So maybe we could say that Lommel-Seeliger  is a good model to emulate all
> > darkness values of Blender Minnaert below 1 wile values above could switch to a
> > darkening slope_map/aoi pattern ?
>
> If you want to emulate Blender's Minnaert in POV-Ray, wait for a couple
> of hours until the next UberPOV release ;)
>
> > And Brilliance parameter would be better to emulate Fresnel as it's more light
> > dependant than viewing angle dependant???
>
> The Brilliance parameter is primarily a poor hack with no physical
> legitimation. I suspect the best way to emulate it would be with
> something like an aoi pattern. While it might indeed have been used as a
> poor man's attempt at approximating a fresnel term, it would have
> succeeded in that only for the outgoing light, ingoing that there should
> be a symmetric term for the incoming light.
>
> (After some research, I have a hunch that the brilliance parameter
> /might/ actually have originated as a failed attempt to implement the
> Minnaert model. But that's just speculation, and it's probably far too
> late to find out the truth about it.)
>
> > Anyway, at the moment I meet a bigger issue, as I see no variation when trying
> > to use the two new models in pov, are they confirmed to work in your Windows 64
> > build?
>
> They should be working fine in UberPOV 1.37.1.1-alpha.8756754, but I'll
> check again.
>
> > The Minnaert shader in POV was the topic of this work:
> >
http://news.povray.org/povray.binaries.images/thread/%3C3f6ccdf7%40news.povray.org%3E/
> >
> > Has it been used for this feature or can it still be added to all the options?
>
> I didn't even know about Kevin's work until right now that you've
> mentioned it (and I'm not sure whether I would be able to dig up his
> code on the Internet). I had even started on my own Minnaert
> implementation already.

Thanks for all the work,  I tried again and it works (I was using a bad version
/#patch syntax...

Three shaders Oren_nayar, Lomel_selliger, minnaert work well. To be nitpicky, I
felt that the minnaert at a value of 2 which is its Blender Maximum value, the
result looked less contrasted than Blender internal renderer. That is to say, in
Blender, faces away from camera appeared lighter while normals facing the camera
were darker than pov result but the overall behaviour is a much closer result
than what we had so far !

How would we use the second fresnel outgoing term ?

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