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Understanding Channels

In Photoshop CS2, an image can have up to 56 total channels, up from 24 in older versions of Photoshop. (The total does not include the composite channel, RGB, CMYK, or Lab, which doesn't actually hold color data.) There are three types of channels:

  • Component color channels: Component color channels contain the basic color information for an image. They are used with RGB, CMYK, and Lab color modes. The single channel in a Grayscale mode image can also be considered a component color channel. Component color channels store the color information for all artwork on layers in the image.

  • Spot channels: Spot channels are used in CMYK images to hold special color information. A spot channel represents ink that will be printed independently of and in addition to the component inks (cyan, magenta, yellow, and black). Spot colors and their channels are independent of the layers in the image and are defined only in the spot channel.

  • Alpha channels: Alpha channels do not hold color information. Rather, they are saved selections and are referred to as masks. Black, white, and shades of gray are used to store the selection information. A hard-edged selection made with the Rectangular Marquee tool would appear by default as a white rectangle on a black background. A heavily feathered selection made with the same tool would appear as an area of white blending through gray to black. Alpha channels can also be used to store transparency information for a variety of file formats.


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