Here's a piece of undocumented Radiosity Voodoo:


If you get stray black splotches in your shot, increasing the global
max_trace_level will reduce their number.


I hope it doesn't kill your render speed though...

These stray splotches are due to an implementation blunder in POV-Ray, and
basically appear in any scene that has reflection or refraction; I'll make sure
it gets fixed in the next 3.7 beta.

I guess these are the ultimate source of a lot frustrating fights with POV
radiosity settings - because to my knowledge there is *no* other way to get rid
of them, regardless how high you crank up the radiosity quality. If you manage
to reduce their number they will grow; If you manage to shrink them, they will
multiply; if you manage to level them out a bit, they will spread out like
pancakes.

The only thing that really helps is toying around with the global
max_trace_level.

There is also a potential similar issue related to global and/or radiosity
adc_bailout; However, I haven't investigated this in detail yet, so I currently
cannot give any advice on how to set these. However, toying around with them may
help as well.

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> If you get stray black splotches in your shot, increasing the global
> max_trace_level will reduce their number.
> ...
> These stray splotches are due to an implementation blunder in POV-Ray, and
> basically appear in any scene that has reflection or refraction; I'll make sure
> it gets fixed in the next 3.7 beta.

   You're absolutely right: I discovered this cause of artifacts while doing 
some tests last month, and I was going to publish an article about it on my 
site, but Real Life got in the way and I forgot about it...

   Usually, just increasing a bit the default max_trace_level to 7 is 
enough, and it doesn't have much impact on regular scenes. It is really 
evident when you have a perfectly square room with reflecting walls: the 
corners receive a lot of artifacts. So I figured out it was something to do 
with max_trace_level without looking at the code... ;)

--
Jaime

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