DBE and circular gradients?

[ftherrmann]

I'm using the current version of PI and have some images with bad circular gradients (less than perfect flats).  I've tried placing DBE model points at various places in the image but am not getting good results.  The circular gradients are lessened after DBE but still very prominant.  I've also tried the ABE with less success. 

Is there an optimum placement for these types of circular gradients?

TIA

Fred

[georg.viehoever]

Try changing the "tolerance" parameter in DBE. Also try if multiplicative correction (instead of subtraction) helps. Placement of the samples is usually uncritical (if placed on background).