All your image's color data is saved in the Channels palette. When you're working with RGB or CMYK images, each color channel holds information for one of the component colors (red/green/blue or cyan/magenta/yellow/black). Each channel is a grayscale version of the image as a whole, using shades of gray, from white to black, to indicate where that channel's color appears (and how strongly) in the image. In RGB images, the lighter the pixel in a channel, the more of that color. When you work with a CMYK image, the light-dark in a channel is reversed, with darker areas showing where more of that color is applied.
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