POV-Ray : Newsgroups : povray.general : Focal Blur banding? : Re: Focal Blur banding? Server Time
30 Nov 2022 05:26:31 EST (-0500)
  Re: Focal Blur banding?  
From: Alain Martel
Date: 27 Oct 2022 12:35:08
Message: <635ab33c$1@news.povray.org>
Le 2022-10-27 à 10:31, Shinzo a écrit :
> Hello everybody. I just rendered the "chess2.pov" from the
> "advanced"-example-directory and noticed a very strong banding effect on the
> chess pieces in front of the camera. Since I know a little bit about modern
> raytracing (I have written some pathtracers for personal use) I asked myself
> what's wrong here since raytraced DOF should NEVER lead to a banding-effect.
> 
> My guess is that POVRay calculates the lense sample positions just once for the
> whole image instead of resampling the lens positions for every pixel.
> 
> If that is the case you might want to change that as it is really sad to see
> those artefacts from Scanline renderers of the 80ties in a real raytracer.
> 
> BTW.: Have you thought about changing the RandomNumberGenerator? It seems that
> sometimes in special cases there appear sampling artefacts (Hyperplane
> artefacts) that seem to come from an Linear Congruential Generator (LCG). If
> POVRay uses an LCG-Generator you should think about exchanging it to an
> LCG/XORSHIFT combination or at least to a generator that uses a combination of
> linear-generation and non-linear-generation.
> 
> 

The sampling is done at the pixel level. And, if antialiasing is in 
effect, individually for each sub-pixel when antialiasing get triggered.
You may :
Try slightly increase blur_samples. Increase gradually, no benefit in 
taking 50 samples when 20 would be enough.
Try adding a minimum value for the blur_samples : blur_samples 9, 20
Try increasing the confidence value (default to 0.9) Max value =1.
Try decreasing the variance value (default 1/128) MUST be >0.


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