"You can get more than 3 masks out of a coloured image if you want to."

You probably can, but I don't know how to, not and keep all 256 levels of greyscale for each mask...

Anyway, I find it confusing enough separating and re-combing the masks with just 3 of them, let alone more. I'll let the experts like yourself do all the difficult stuff:-)

Cheers,
Diolma