nstance of that color in the file. A different color may be substituted
for the selected color. Do that for all selected background colors by

Thaks a lot for your comments. I have used Picture Window for similar
purposes. Briefly, the procedure was to make an exposure near the image, then
remove the stars in the second image and use this as a template for a flat
field image. This method is tedious while the Olympus method is so much more
elegant.