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.

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