Ta, JB. I will read up about that and give it a try. I managed something "acceptable" at low
magnification, and certainly better than it was.

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Hmm, that was fast! I did a search on "sharpening using LAB color"
and there are heaps of refs. This is the first one:
https://www.google.com/search?client...U4-EPt5O4wAs21