Photoshop Tutorials - Operations with Alpha-Channels
Operations with Alpha-Channels
If when saving selection you choose the name of existing channel for the Channel setting in the dialog window that opens then you must select how the new and old channel are combined? You can set the way old and new channel content interact in the Operation field of this same dialog window:
Replace Channel - replaces the content of the channel with the new selection.
Add to Channel - adds new selection to the old selection in the channel
Subtract from Channel - removes new selection area from the old selection
Intersect with New Channel - saves the areas of new and old selections that intersect.
Note that last two operations can be performed only if the selection areas intersect, that is obvious.
There are some options to play with when you load the channel as well. Such operations are possible when we load the selection to the file that contains some selection. All of the operation options are standard so I will not go over them again.