Is that your shot? I saw it last week in a video tutorial on how to do masking. I can't find it at present, but here's another one that seems to go over the same ground. It's a little complex to explain, so watching a tutorial is best. But it does work well in CS6. Try searching 'layer mask tutorial photoshop' in Youtube as there are others.
Hi rob, The image was taken from a YouTube video on masking, but I don't remember the title. I will search YT for more videos. Thanks Luís