While working with Ufraw I noticed one thing that may help solve the long standing but with uniform blue color (when anything is changed in the luminosity tab, zones of the image with uniform blue colors may present artifacts in the form of solid black zones). I have noticed that, even when no blue color is present, when any small modification of the parameters in the luminosity/saturation tab introduces a dramatic change in the image (and in the histogram) w.r.t. the image with all the parameters in this tab set to 0 . It looks like, when any of these parameters is set, there is a kind of scaling going on. Look at the differences in the dark parts (e.g. the clothes of the model or the shadowed part in the bottom right) and the histogram.
As you may remember, I have already tried looking at the code for this problem, but it is very difficult to understand what happens without a specific knowledge of the library used by this portion of ufraw. I (kind of) guess that the problem happens in the scale_curve function of ufraw_developer.c. Is there anybody with some knowledge of these libraries and willing to look into the problem?
the long standing BUG, sorry!