[Radiance-general] What's causing these artifacts???

[Marcus Jacobs]

Dear Group

In some of my recent renders, I have encountered some very specious 
artifacts. I generally specify a high number of ambient division (usually 
around 3072) and ambient super samples (500-1000) for my renders.

The first ones are these mysterious dark splotches:

http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=b3e9&.dnm=4bcbre2.jpg&.src=ph

http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=b3e9&.dnm=c76fre2.jpg&.src=ph

I really can't figure out what's causing these. I am unsure if this is 
caused by poor interpolation. Also, occasionally I have come across the 
following bright spots:

http://pg.photos.yahoo.com/ph/marcdevon/detail?.dir=b3e9&.dnm=e02ere2.jpg&.src=ph

No matter how many ambient divisions that I specify (I went up to 16,000 
ambient divisions with 2000 ambient super samples),  I can't get rid of 
these bright spots. The problem with these particular artifacts is that I 
can not predict when it will occur. What I need the most when performing 
renders is predictability. Does anyone have any ideas?

Thanks

Marcus