The Alpha to Selection command creates a selection in the current layer from the alpha channel, which encodes transparency. Opaque areas are fully selected, transparent areas are unselected, and translucent areas are partially selected. This selection replaces the existing selection. The alpha channel itself is not changed.

The other commands in this group of operations are similar, except that instead of completely replacing the existing selection with the selection produced from the alpha channel, they either add the two selections, subtract the alpha selection from the existing selection, or create a selection that is the intersection of the two.