Attached Link: http://www.soft-rabbit.com/

Unfortunately, it is not. The BUM conversion is some sort of weird emboss effect, and there is no trivial way (like channel operations) to reverse it. I wrote a filter called "GreyBump" for GraphicConverter which performs exactly this (BUM back to greyscale) with some minor loss of quality, but unfortunately it is currently Mac-only. I'm considering possibilities to eventually port the feature to PC, but I can't promise you anything in the *very* near future, I'm afraid...