I've got a question regarding how flat division is actually implemented in ASTAP.
The documentation on the web site describes this in the stacking process as:
2) The combined dark frames called master dark will be subtract from the light frames to extract the pure deep sky signal.
3) The combined light frames, dark compensated in 2) will be flattened by dividing it by the master-flat resulting in the final deep sky image. Prior to this a small 2x2 or 3x3 median filter is applied the master flat to reduce noise.
Does that actually mean, that flat division happens after
alignment and stacking of the dark compensated light images? That would seem wrong to me, as after alignment (translation, rotation, scaling), the light image does no longer match the flat image. Dust bunnies are no longer in the same place as in the flat!
In all other stacking software I know of, flat division is part of the calibration / pre-processing step that is done for each source light image before
alignment (registration) and stacking.
Is this probably just wrong wording in the documentation on the web site?