Understanding Photoshop Channels


There are two types of channels in a Photoshop document. Color channels are graphic representations of color information. They are an integral part of the image. Having access to this information enables you to perform powerful modifications and corrections to the image s appearance and color relationships. Alpha channels are graphic representations of selections that have been stored for later use.

Color channels are composed of information segregated by color. Each color channel is actually a separate grayscale image. When you view the color channels superimposed on each other in an image, you see the full-color composite image. For a detailed description of color channels, see Chapter 3, The Nature of the Beast.

An alpha channel is also a grayscale image. Like a color channel, it can support 256 shades of gray. Unlike a color channel, however, an alpha channel does not contain information that contributes to the image s appearance. And instead of the values of gray representing tonality or color, they represent the areas of opacity, semitransparency, or transparency of a mask.

Photoshop provides many features that isolate areas of an image so that you can perform edits and adjustments to a specific region. It s helpful to think of an alpha channel as a tool that you create, store, and later use to isolate an area so that a tool or command can ultimately be applied to it.

Bear in mind that although alpha channels are stored selections and do not affect the way the image appears, they are perceived by Photoshop as part of the image, and therefore increase the file size of the image proportionally each time you save a selection. Photoshop supports a maximum of 56 channels in a document (except in bitmap images which don t support alpha channels). Images with alpha channels can become quite large and consume a great deal of disk space, so it is best to delete your alpha channels when you are sure you are done with them.




Photoshop CS Savvy
Photoshop CS Savvy
ISBN: 078214280X
EAN: 2147483647
Year: 2004
Pages: 355

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