Can someone tell me what the Quick Mask tool is for?
I've seen it quite a few tutorials ... and while I know how to turn it on and turn it off, I'm never quite sure what it does
Well, painting with black and white on a mask reveals and hides pixels on that layer, that you know. But usually when you do so, you will either see your pixels or you will see what lies underneath, the quick mask mode lets you see the layer in it's entirety while you paint your transparency, you will see red as what will become your mask but you still see the layer - I hope that made sense, as I was typing it, I couldn't really figure out if I could explain it better. People used to use it to extract something from it's background, but with the extract tool, that is no longer necessary. When you exit quick mask mode, you will have a selection again, rather than a mask.
Quick mask is a good way to make a selection, using any of the painting tools, your colors change to black and white automaticly, black paints, white erase's, the color red shows where your selection will be. When you exit quick mask you will have the "marching ants" to show your selection, Press cmd/ctr-J and you will have a new layer with your selected area empty, if you want your selected area to show but the background to be empty go to the top, choose select>inverse before you press cmd/ctr-J
I hope that helps.
I use quick mask more then any other selection tool because it gives you total control.
[Edited on 2/13/2003 by Stellor]
You can also use filters on the quickmask to produce really weird selections.
This can help you achive some interesting affects.