Hi Gerhard.
I have a number of images of the same object taken over several nights and involving meridian flips, so the frames don't quite line up. For one reason and another, i don't have flats, so I want to correct for vignetting. Each image has a simple background correction, but if I combine all images the background becomes more complicated. So i think it is better to keep the ABE application simple and correct before combination
Geoff