In digital image-processing programs (such as Adobe Photoshop), one of two basic types of "channel" which comprise an image. A channel is essentially one portion of a digital image. There are color channels and there are alpha channels. A color channel is one of three separate channels (one for red, one for green, and one for blue), each of which contains a grayscale image corresponding to one of the three primary colors making up the image. (For example, the red channel contains only the red portions of the image, the green contains only the green portions of an image, and the blue contains only the blue portions of an image). An alpha channel, on the other hand, is a kind of "wild card" channel, and can store other user-selected portions of an image, or even other images that can be intermingled with the other channels to provide various effects to the image as a whole. Most image-processing programs allow for many different channels to be added.
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