In this section, we show you two specific uses for masks and channels that cannot be accomplished by other means.
The natural mask of an image is a quick way to generate a mask that selects the subject of an image. This particular mask is not always accurate, but, in many cases, it yields good results. This concept is the brainchild of Carey Bunks, author of an excellent, early book about GIMP, Grokking the GIMP (New Riders, 2000).
Figure 14-37. The Channels dialog
Figure 14-38. The Threshold tool ...