Steve,
I think robin is trying the real unshape mask as mentioned right at the top of the thread...
Robin,
What program are you using? I used Photoshop, and didn't exactly follow the instructions to the letter. Where the method talks about "apply image", I just used layer subtract. Essentially the same thing, just easier. Try resetting the white point in levels if the final image is too dim, and then stretch the levels some more to acheive a balanced result. Also reducing the brightness of the mask will increase output brightness, but you will have less unshape mask.
Hope this helps
Cheers
Rob