People who print colored pictures cheaply take advantage of the way we perceive by using this "process color" phenomenon. They print graphics as dots. If you have a color printer for your computer, you will see that in general the printer uses this technique as well.

For this system to work, many things have to be right. For example, each color is printed as a grid of dots. Where the color is the strongest, the dots are bigger; where it is weak, the dots are smaller. (In fact, as you will see in the activity, in a strong color, the grid is really white dots on a colored field, rather than the other way around.) When you have several colors, however, you have to make sure the grids of the different colors do not make strange patterns (called Moire patterns) that are not in the picture. So, engineers design printers not only to put the grids at special angles to one another but also to offset them just right.

A typical magazine or newspaper picture is printed in four colors: Cyan, Magenta, Yellow, and Black—also called C, M, Y, and K. (In this activity, only the first three are used.)

At the time of the Impressionists, some artists, notably Georges Seurat, began to paint with tiny dots of color. They did not limit themselves to dots of only a few colors but used a diverse palette. Doing this, they produced paintings which reflected precise colors and textures when viewed from a distance. But if you view the paintings up close, you can see the dots—just as you find with the less-sophisticated "magazine" effect.

At the National Gallery of Art web site, you can see examples, such as Seurat's The Lighthouse at Honfleur. When you use the link, be sure to click on "detail images" to see close-ups. Then click on the details themselves to get an even closer view.

You need this real-world experience to see how a few colors can create an array of many colors. Get a good magnifier, a magazine, and a photograph. Compare the colored pictures. The magazine picture really is made from dots, and the photograph really is formed by solid colors.