Photoshop CC: The Missing Manual, 2nd Edition

How Color Works

The images you see on computer monitors and TVs are made of light; without light, the 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 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.

Note

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 5-1). Does that 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 the three lights overlap. Interestingly, you also see cyan, magenta, or yellow where two of the three lights overlap (also shown in Figure 5-1). Areas where no light is shining appear jet black.

Now it’s time to talk about printed color, which—brace yourself—works in a totally different way.

Printing presses use what’s called a subtractive color system, where the colors result from a combination of light ...