I'm photomerging slides that were taken as panoramas in the 1980s. One of these panoramas is rather dark and won't photomerge, but if I lighten the images, then they will. I want to keep the original dark tones, and I'd rather not lighten (for the photomerge), and then darken. I'm a bit of a purist in regards too many edits.
Is there a way I can apply, say, a Curves layer, and photomerge with the Curves layer intact? Or any other technique?
If not, what is the most reversible way to increase brightness and then revert? Reversible meaning ending up as close as possible to the original brightness.
As an aside: why is that my slide panoramas so readily photomerge, sometimes with only 5% overlap, whereas digitals seem to require a lot more overlap?