Thanks Christian - although I'm a little unskilled in this area.I tried varying the water mask 8 bit values between 0 ( black , water) and 255 (white , land) and Resampler just rounds back to 0 or up to 255 with the result of either full water effects or land and nothing in between.Have I misinterpreted your post ? Not sure how to set the alpha component to a non interger as you suggest.