Absolute Beginner's Guide to Digital Photography

1. Open Photoshop (any version) and open a color image. Save the image with
   a new name to preserve the original.


2. If the image is not in RGB mode, convert it to RGB by clicking Image, Mode,
   RGB Color.


3. Open the Channels palette, if it isn’t already open, by clicking Window,
   Channels.


4. Click one of the color channels in the Channels palette. The other channels
   will turn off and only the selected channel will display.

Again, an RGB image has three color channels plus the composite channel.

Individual color channels are displayed in Photoshop as thumbnail images in the

Channels palette. The composite channel is labeled RGB and represents all three

channels together. When the eye icon is present next to the composite RGB channel’s

thumbnail, the image is displayed in full color in the main image window. When

working with channels, it’s always easier to see your edits when the composite RGB

channel is unchecked. It’s best to view the individual color channel’s thumbnail

images in black-and-white (instead of color) because they are easier to compare with

each other.

Color channels can be viewed individually in the main image window by making

the other channels invisible. Channels are turned on or off by clicking their eye

icons. In Figure 17.1, only the blue channel can be seen (as a black-and-white

image) in the main image window. The composite channel and other single color

channels have been turned off (their eye icons are not visible).

Using Masks to Create Selections

Channels store masks. Masks are the most advanced way to create selections. Think

of a mask as a sheet of plastic that lies on top of an

image. Masks restrict the editing performed to the

image beneath the mask.

In some ways, a mask is like a stencil. You can edit

the colors and tones of the image beneath wherever

you cut holes in the plastic, but nothing can

change wherever the plastic is solid because the

image is masked (see Figure 17.2).

One advantage of masks is their variable density.

Whereas ordinary selections have feathered or

antialiased edges, a mask lets you make any part

of a selection opaque, transparent, or in-between.

Where a mask is transparent you can edit the

image normally. Where a mask has partial density,

CHAPTER 17 THE IMPORTANCE OF CHANNELS 257

Before a mask can be

used to edit an image, it

must be converted into a selec-

tion.