Ok Andrew, this is exactly what i do.
Before the evenings imaging I take my flats, scope pointed directly over head into the clear, just after sunset sky, about 15 or so.
Then take my images of the object of choice, in raw, with ICNR set on 2, that's not an issue.
Once the images are aquired I convert them to 16bit tiffs in the the canon software (Digital Photo Professional)
Then I open up Image Plus and open the Auto Image Set Processing window.
Load the Lights, the Flats etc, and click on process, here the lights are calibrated etc
Once processed I click on Align TSR, which opens another window, and then I click Centroid, and Translate + Rotate, and Comon Point of Star.
Choose my Star and go through the motions of doing each Image, when done it click on Common Angle Defining Point of Star, and go through the motions again.
When this is done I Check for a reference image and click align, once aligned I average combine and end up with a (Ave Combined Image).
This is automatically save as the combined image, or I could give it another name.
I leave this image open and then do a Auto, Digital Development on it. and adjust the Histogram and sliders accordingly.
When I'm happy with the result I save it under a different name as a 16 bit tiff,m and then take it to PS2 for some extra if needed, and that is about it Andrew,
So why the central brightness in all my images from this program. buggered if i know.
I have had this problem for some time now and constantly had to darken my image to compensate for it.
Andrew I can come up with a solution, or suggest something please do.
Leon
