Calibrating is clipping to much ? (BatchPreprocessing)

[Thomas]

After I run BatchPreprocessing the calibrated pictures are always clipped for some reason.

I did some tests to may figure out what could by wrong , so I was running BatchPreprocessing just with MasterBias or just with a MasterDark or with all (Bias/Dark/Flat) but the result was always the same, the calibrated pic are always clipped. (shown in the added pic) .

I cant remember I noticed this also in earlier PI versions, but maybe I have just  accidently adjusted a parameter/ setting somewhere, or is it a bug ?

The left pic shows the original 60 seconds exposure  , the right pic the same pic after calibrating. (with their zoomed in histograms)

PS: All frames captured with SGP so there was not added a pedestal value.

Any hint is welcome.

Thomas

[sharkmelley]

If the background level in your lights is extremely low then subtracting the master bias can sometimes lead to clipped values, simply because of the randomness of the data.

What is the mean and standard deviation in your master bias?  What is the mean and standard deviation in a star-free background area of your light frame?

Mark