Thanks for the explanation. I might not have explained my questions well. I have a pretty good understanding of calibration and calibration frames, at least I thought so. Let me try again:
Until now, I removed bias signal from my flats with a Master Bias, but not from either Lights or Darks. My Master Dark, therefore, contains bias and dark current, and therefore removes both from the Lights when the Master Dark is subtracted from the Lights. As I understand it, that is the fairly common approach to calibration. However, since my ASI1600 suffers from the odd bias frame issue I decided to try the FlatDarks approach, instead of using a Master Bias. My uncertainty is over whether that FlatDark should be treated as a [modified] Master Bias or as a "short" Dark. Since Bias frames technically do contain a small amount of dark current, albeit a very small amount, and dependent on the minimum exposure time of the camera, in my mind Biases, FlatDarks and Darks are essentially all the same - they all contain bias and varying amounts of dark current. There are a number of lengthy threads on FlatDarks debating more or less that point, and making the argument that the amount of DC subtracted from Flats with a 0.1sec (or so) FlatDark would have no practical effect when that calibrated flat was subsequently divided into the Light frames, and therefore a FlatDark can be treated as a Bias. If those points are true, then it seems that treating the FlatDark as a Bias makes sense and I can see why one would assume that the FlatDark should be added to PI's "ImageCalibration" for Flats as a Bias, and not as a Dark, though I'm not entirely certain it matters. I can't find any thread where this point is raised, but noticed you add it as a dark. Hence the question in my earlier post - why as a Dark Rather than as a Bias?
Edited by Hawkdl2, 14 June 2020 - 03:25 PM.