This command substracts from the selection image pixels corresponding to pixels with opacity more than 0% in the layer mask. White pixels (100% opaque) in layer mask will give pixels fully substracted from the selection. Grayscaled pixels (1% to 99% opaque) will give a feathered selection. Black pixels (0% opaque) will not be substracted. Substracted pixels are not removed: they are not included in the selection. The layer mask is not modified by this command.