poser 4 bumfiles are red-to-green. AFAIK changing 'em to greyscale won't work. we useta create greyscale displacement maps, then poser would convert 'em to red-to-green, based on the first derivative of change in brightness. hence one would wanna use the original greyscale map from which the bum file was generated. bum files don't work in anything but the poser 4 renderer (see manual).