CHAPTER 17 THE IMPORTANCE OF CHANNELS 259Seeing Through a Mask
A mask can be easier to use than an ordinary selection because of its visibility.
Ordinary selections are visible because their edges are marked by a moving marquee
(the marching ants). But if it’s a feathered selection, the marquee doesn’t show
exactly where its edges are. A mask is better; you can see all of it.
A mask appears on the monitor as a blanket of color
over the image. The colored blanket is most dense
where the mask is fully opaque and is transparent
where the mask is transparent. You choose both the
color of the mask and how opaque you want it to
appear on the monitor. (Usually you don’t want a
mask to be so opaque that you can’t see the image
beneath it.) You can also temporarily make the
mask invisible if it blocks your view of what you’re
doing.
Adobe Photoshop treats masks as grayscale (8-bit)
images. This has significant consequences. Because
the software treats masks like images, you can edit
them like images. This means you can use a brush
to paint on a mask, making the mask either more
opaque (blacker) or more transparent (whiter).
Because masks are treated as images, you can also paste shapes and other images
into masks. For example, you can put type into a mask; the shapes of the letters can
then be transformed into colors or effects (see Figure 17.4). You can paste images
into masks (but only 8-bit grayscale images).
Selections also can be turned into masks. Clicking the Save Selection As Channel
icon in the Channels palette turns the selection into a mask. Why do this? Most
complex selections start with a simple selection, as you might make with the Lasso
tool or the Magic Wand; by turning them into masks, you can edit them more pre-
cisely. Finally they are turned back into selections. This might sound roundabout,
but it is a powerful technique. For example, it is helpful when creating extremely
complex selections, such as around someone’s hair.A feathered selection
blends into the area out-
side the selection. In Photoshop
make a selection, then click
Select, Feather.