For the most part, Elements hides access to channels, even though channels are a fundamental building block of a Photoshop/PSE image.
In full Photoshop, you have direct access to the channels. Each component of each color model has its own channel – the RGB model has an R channel, a B channel, and a G channel, the CMYK model a C channel, M channel, etc. These let you work on specific colors within your image. You can apply sharpening to just one channel, for example. They’re very handy for lots of image manipulation.
The "right" way to achieve color balance, for example, is to work with individual response curves for the individual color channels – set the white, black, and midtone points for the R G and B channels (assuming you’re working iun the RGB color model).
Full PS also has "alpha channels," which let you store various other kinds of information about your image. In Elements, when you save a selection, you’re really creating an alpha channel; if you open the image in Photoshop, your saved selection will appear in the Channels palette, right along with the R G and B channels.
The main place most Elements users encounter channels is in the Levels palette. Here you can use them to vary the relative intensity of each channel. They’re useful in eliminating color casts; for example, if you have a green color cast, you can use the G channel to reduce the amount of green; or if you have a magenta color cast, you can use the G channel to increase the amount of green. They’re also useful in varying the relative amounts of each channel used to convert a color image to B&W for better control than you get with just the Convert to Grayscale option.
Richard Lynch’s toolset has a set of separation tools that break out the individual channels for PSE users. It’s a weak substitute for the tools available in full PS, but at $30 or so Richard”s book is a lot cheaper than full PS <g>.
