Color Channels in CS5
When you work with an image in Adobe Photoshop, the image has at least one (but typically more) color channels. A color channel stores information about a particular color in a selected image. For example, an RGB image has three color channels: one that handles the reds (R), one for handling green information (G), and the last for information about the blues (B).
You can have, in addition to the three color channels, an alpha channel, which can hold the transparency information about a particular image. If you’re working with a file format that supports transparency, you can add and use the alpha channel to save alpha information.
You can also use an alpha channel to save a selection. By choosing Select→Save Selection in Photoshop, you create an alpha channel with your selection saved to it. You can choose Select→Load Selection and choose the channel to reload your selection at any time.
In Photoshop, you can access the channels in your image by choosing Windows→Channels. When the Channels panel opens, you can toggle the visibility of each icon by clicking the eye icon next to each channel.
Using color in documents is one of the most important considerations in creating your projects. The colors you use, the mode you use them in, and even the way you select colors make a difference in the way you create a document and the final output of that document. Even though you can create a document that looks the same on a monitor in different color modes, how that file prints on paper is a different matter.