Am 23.09.2010 11:34, schrieb Der_Minimalist:

> I use several area lights in my scene which highlight objects on a somewhat
> reflective plane. However, the light doesn't fall off completely smoothly but
> there seem to be darker concentric lines around the highlighted areas. The lines
> are virtually absent (or overlapped) in well light areas but become noticable
> (with decreasing interval) in parts where the light starts to fade.

The dark concentric lines are actually an optical illusion, occuring at 
the boundaries between areas of very slightly different brightness - 
just enough for the eye to notice the contrast at the boundaries, but 
not enough to perceive the adjacent areas as having different brightness 
as a whole.

The proper solution to this, as Florian already pointed out, would be to 
introduce a tiny bit of noise (ideally corresponding to +/- 0.5 bits).

Other than using crand, you can also use a higher-precision output 
format (OpenEXR, or 16-bit-per-channel variants of classic formats; 
Radiance HDR may also do, provided the gradient colors are not too 
saturated), then convert to a standard 8-bpc format using an external 
tool that supports dithering. (IC is my favorite tool for this kind of job.)

(Note that in this case, the render preview will still show the same 
banding artifacts, although the OpenEXR output will be perfectly smooth.)

Unfortunately, POV-Ray does not support automatic dithering for 
low-precision output formats yet.

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