On 02/02/2016 07:03 PM, Norbert Kern wrote:
> "Norbert Kern" <nor### [at] t-onlinede> wrote:
>
>> Of course I can send more scenes with black pixels...
>
>
> I uploaded a collection of 12 materials, which give black pixels in combination
> with a very simple scene setup.
>
>
http://news.povray.org/povray.binaries.scene-files/message/%3Cweb.56b13fdfffbcf045dea14abf0%40news.povray.org%3E/#%3Cwe
> b.56b13fdfffbcf045dea14abf0%40news.povray.org%3E
>
> Averaging normals seem to be a good way to cause such problems...
>
>
> Norbert
>
>
Hi Norbert,

I think the trigger is normals with turbulence scaled very, very small. 
Perhaps the shape is seen inside out. Try replacing the averaged normals 
in your primitives3.pov with the single normal :

normal { bumps 0.6 warp {turbulence 0.5} scale 0.01 scale 0.05 }

If the problem is still present as it was for me, try :

normal { bumps 0.6 warp {turbulence 0.0} scale 0.01 scale 0.05 }

or

normal { bumps 0.6 warp {turbulence 0.5} scale 1.01 scale 0.05 }

and see if the problem goes away for you too. If so then I guess 
understanding how small is too small to use turbulence with normals, 
whether a real bug etc.

Radiosity is sending out its own rays of course. I am not sure why those 
rays seem more sensitive to what ever is happening than do rays directly 
from the camera.

Aside: Wish I had your machine! I had to cut WAY back on the radiosity 
settings to get things to turn reasonably for me & some chance this 
affected results though I was seeing similar artifacts to those posted.

Bill P.

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