The images you see on computer monitors and TVs are made of light; without light, these screens would be completely dark. While your eyes are sensitive to hundreds of wavelengths of light (each associated with a different color), it takes just three—red, green, and blue—to produce all the colors you see onscreen. So to create color, monitors add individual pixels of colored light. That’s why the onscreen color system is called “additive.” Each tiny pixel (short for picture element) can be red, green, blue, or some combination of the three. All image-capture and input devices—digital cameras, video cameras, and scanners—use the additive color system, as do all digital-image display devices.
Onscreen images are also called composite images because they’re made up of a combination of red, green, and blue light (also known as RGB).
In the additive color system, areas where red, green, and blue light overlap appear white (see Figure 6-1). Does that sound crazy, or does it ring a bell from high school physics? Think about it this way: If you aim red, green, and blue spotlights at a stage, you see white where all three lights overlap. Interestingly, you also see cyan, magenta, or yellow where just two of the three lights overlap (also shown in Figure 6-1). Areas where no light is shining appear jet black.
That’s how computer monitors and TVs create onscreen color. Now it’s time to talk about printed color, which—brace yourself—works in a totally different way.