Hi. You can do this:
- Press the D key for activating the Foreground/Background default colors (Black and white).
- Load a selection of the one layer mask: cmd + click the Layer mask icon
- With the selection active select other Layer mask icon and use Cmd + Backspace or Cmd + Option + Backspace for add or subtract areas from this mask.
[Replying to the thread starter]
I have never heard of doing what you describe, but I wonder if you are thinking of using Calculations to combine multiple Alpha channels? I'm trying to find a decent tutorial for you, because it is a wee bit complex.
I 'think' this book exert from Bert Monroy covers it (I have not read it all). It was Bert who introduced me to the technique in one of his Lynda.com tutorials (I think from the Times Square series).
I am not sure the above guides cover what I am talking about. Using Calculations to combine two channels into an Alpha channel (mask) is very powerful, but Bert used both layer and vector mask if I recall correctly, which suggests part of his selection was made with the pen tool. I'm away from my computer for a couple of hours now, but will look again later.
[EDIT] A bit of a 'whoops' moment there. The forum threw a wee hick-up as I was trying to reply to the OP, and I ended up quoting Marliton. I'll edit out the quote, but sorry if it confused before I noticed my cock up.
Thanks, Marliton and everyone else. After my post I fooled around with it and figured it out as you describe it. After activating the marching ants on the target layer mask, then hover the "hand" cursor over the secondary layer mask you wish to add to it, or subtract from it.
CTRL+SHFT will reveal a "+" on the hand cursor, and CTRL+ALT will reveal a "-". Decide whether to add or subtract the secondary layer mask then simply click it. It will be added or subtracted from the target layer mask. This is obviously for PC, Marliton described the technique for MAC.
In the olden days of Ps CS4 we would click and drag the secondary mask to the primary mask (with the appropriate keys held down to implement adding or subtracting the secondary layer mask to/from the primary), now there is no dragging involved.