Unsavory characters
One way to find the remaining cosmic rays and other defects is to
compare the four images taken with the four different filters.
Another way is to compare the pictures with the image profile of a
point source such as a star. If we see a sharp bit of light that
doesn't have the right profile to be a star, it's probably a
cosmic ray residual or other defect that we need to flag and
remove. This image shows the remaining undesirable bits flagged in
white against the desired image, shown for the moment in red to
ease visibility.
Now let's delete the remaining "flurries" and see what we've got.