Eric Stevens
It's not a reversible process as it is conventionally defined.

nospam
yes it is.

someone can unsharp mask today and remove it tomorrow and put it back the day after that.

Eric Stevens
You don't know the formal definition of a reversible process, do you?

nospam
the following week, that same someone can remove all colour (convert to b/w) and the week after that, can reverse that, exactly how it was in the original image, because it *is* the original image.

that's what just about everyone would call reversible.

Eric Stevens
I seem to remember that you once claimed to be familiar with Claude Shannon's seminal paper "A Mathematical Theory of Communication". If that is correct you should be able to tell me what he called a reversible process in that context.