VrayEnvironmentFog sampling problem

[racoonart]

I found a strange thing happening with environment fog sampling on bright spots (like reflections). Please see image below:
On the left you see the beauty pass with a bright blurry reflection highlight. On the right there are three images with different subdivision values:
#1: 16 samples, you can see a darker area where the big bright highlight is
#2: lowering the subdivisions will results in a more noisy but dark-spot-free pass
#3: same result with really high values

I thought it could be the cutoff threshold and tried lowering it to zero but it didn't change anything.
In another scene I can even see a kind of dark halo around bright spots in the beauty pass. I can't lower or raise the subdivisions there so it's quite a problem.

[edit]
I attached another image where the problem is even visible in the beauty pass (image zoomed)

[vlado]

What are your color mapping settings? Do you have the "clamp output" option in the color mapping section enabled? It could be that V-Ray sees the very bright highlight and does not trace enough rays to smooth out the environment under the (valid) presumption that more samples won't have an effect on the result anyways because of the clamping.

Best regards,
Vlado

[racoonart]

No, in both scenes color clamping (and subpixelmapping) is deactivated. Furthermore i just found some other places (not only very bright areas) where those dark seams appear.. and even if there is no need to trace more rays to get a clean result in the beauty pass there shouldn't be a dark spot in the REs... it's very ugly in the comp later on.
[edit] The problem is that there are really "black holes" in the pass which don't fade out or something (like the speculars/reflections), that's why there are dark seams everywhere (on the chairs for example)

[vlado]

Ok; can you get me an example scene to vlado@chaosgroup.com?

Best regards,
Vlado

[racoonart]

File sent I extended the scene a bit, now it's very clear what the problem is

[racoonart]

Any news on that issue? I can't go back to 1.5 right now, so it's a bit annoying to be without environment fog...

[racoonart]

Sorry for digging out this old thread but i just tested the scene again with 2.0 sp1 on 2012 and the problem still exists


[edit]
Ok, i just found out that there might be a problem with the DMC sampler. When i lower the noise threshold to 0,005 (before 0,01) i get this result. Especially the dark buckets are interesting.