You can create a mask from a selection, an alpha channel, or another image. You create a mask and the mask adjusts itself to the size of the image to which it is applied. If you need more precision, you have to create a mask specifically for the image on which you are working. Add Mask from Image Dialog Box Options Source of Luminance Creates a mask based on luminance value. Any Non-Zero Value Creates a mask with no gradation.
Black pixels cover completely.
All other pixels are transparent. Source Opacity Creates a mask based on opacity. A Sharp Edge Mask Open a new file. Set your foreground color to white. Right-click to open the recent color dialog box.