Inside Photoshop® CS

Channels: A Definition and the Keys to Mastering Them

Let's pretend we can revisit grade school and are listening in on a lecture concerning how light is broken down into components. The professor whips out a prism, places it near sunlight (which is very close to absolute white), and ker-blooey…the white light is broken down into its components.

Although all this is very illuminating, it does not describe the principle of additive primary colors—the colors your computer monitor uses to make up all the colors you can imagine. What we need to do in our imaginary trip back to 4th grade is to come up with an equally imaginary device—a perverse prism—that will allow us to do the exact opposite of what a prism does. In Figure 4.32, you can see my own ...