Color Channels

When you acquire an image, the color information that the scanner sees is separated into red, green, and blue components . Photoshop configures this information into a red, green, and blue color channel plus a composite RGB channel, which displays the entire image in full color. Think of each color channel as a separate, transparent color overlay consisting of red, green, or blue pixels. The combination of the three color values, when superimposed over each other, produces full color.

The channels can contain 256 possible shades of either red, green, or blue, because each pixel on the channel contains 8 bits of tonal information (see the upcoming sidebar titled Bit Depth ). The computer processes the information in each channel as an independent grayscale image. Each pixel is assigned a specific numerical value, where the darkest shade (black) equals 0 and the lightest shade (white) equals 255.

By default, individual color channels are displayed in grayscale because the subtle variations in contrast are easier to see when looking at the channel in black-and-white. You can, however, see the independent components of an image in color. To see your channels in color follow these steps:

Choose Window ’ Channels.
Choose Photoshop (Mac)/Edit (Win) ’ Preferences ’ Display & Cursors.
In the Display options check the Color Channels In Color box.
In the Channels palette, click the thumbnail of the red, green, or blue color channel to display that color component of the image on-screen.