Paul Leyland

Further to Jeremy’s comment: the use of dark and flat frames goes a long way to to cleaning your image of truly hot and cold pixels.  However, it cannot deal with either cosmic ray hits or satellite trails close to the VS or a comparison.  If you see any anomalously faint or bright estimate, take a close look at the corresponding image to see if there is an obvious reason to reject it.

In my case, I throw away perhaps two estimates per thousand.  It’s only when processing thousands of images does it become really noticeable.