In living color.

All the pictures in this magazine are optical illusions. Don't believe it? Neither did I. Then I took a closer look.

What's the first thing you do when you open a copy of Science World? You look at the pictures, right? I'll admit it, so do I. But I never took a really close look until I visited our printing plant last spring. There I discovered how printers trick our eyes into seeing colors that aren't really there.

SPOTS BEFORE MY EYES

My first view of the Quad/Graphics plant in Pewaukee, Wisconsin, told me something big was goin on. Huge eighteen-wheeler trucks were pulling in and out of the lot when I arrived.

But the giant trucks were nothing compared to what I saw inside. The pressroom --the size of an airplane hangar--contained eight mammoth printing presses, each about a block long and two stories high. forklifts whizzed about carrying tree-trunks-size rolls of paper, tooting horns so they'd be heard above the mechanical roar.

It's no surprise that the people working in the plant looked small. What did surprise me was that so many of them seemed to be concerned with something even smaller; I saw them everywhere peering through magnifying lenses. With everything around them so big, I wondered what they could possibly want to magnify.

"Dots," said Quad's Dennis Balas, whose job is to find ways to improve print quality. "What we do in printing is we break [the pictures and the words] into little dots," he explained. And by printing the dots, "we fool the mind into thinking it is seeing something else," namely, the pictures and the words.

I started thinking of my last trip to an art museum, and the paintings I saw in the style called pointillism. It was used by the nineteenth-century French painter Georges Seurat, among others. Saurat covered his canvases with colored dots to create the images he wanted to show. From far away, your eyes cannot resolve the dots (that is, you can't see them individually). But you can recognize the images and patterns that the many dots form.

The dots that make up the pictures in magazines like SW are much smaller than Seurat's, your naked eyes can't resolve them at all. That's why the workers at Quad look through magnifying lenses to see the dots when they want to check that they are printing correctly. (Use a hand lens to take a close-up look for yourself, or see the magnification on p.9.)

DOTS OF COLOR 

Of course, not all painters paint with dots. So why do printers use them?

"We have to separate [pictures] into dots to create the illusion that there are many colors on the page," said Bob Schrimpf, a technician who helps transform artwork into the metal press plates that print our pages at Quad. It just wouldn't be practical to build a press that could print the thousands of colors magazine pictures contain. "So we only print in four colors," he said.

Four special colors, which, when combined using dots, can produce a wide range of the colors your eyes can detect. They are the three primary pigments: yellow, magneta (a dark pink), and cyan (a blue-green)--plus black (see diagrams, p. 10 and below.)

KINDERGARTEN KOLORS

Magenta and cyan may surprise you if, like me, you're used to mixing yellow, red, and blue (which we sometimes call primary "colors") to produce a variety of other colors. But if you know something about the way our eyes see color, you'll see that, in printing, red and blue just won't do.

First of all, what our eyes detect when we see is light energy -- particular wavelengths of electromagnetic radiation. Our eyes have receptors for detecting three distinct groups of wavelengths: reds, greens, and blues.

These colors of light are the true primary colors. When their wavelengths are combined in different proporations, they create all the colors of the spectrum.

For example, when an even mix of red and green light wavelengths (not pigment) reaches our eyes, it stimulates both our green and red receptors. Our brain interprets the combined signal as "yellow." "White" light is an even mix of red, green, and blue wavelengths. (Try overlapping beams from flashlights covered with color filters to see for yourself).

REFLECTIONS

Most of the time when we see color, however, we are not lookint at beams of colored light. Instead we are looking at light reflected by objects. The objects are embedded with pigments that absorb some wavelengths of light energy and reflect others. "What we see is what is not absorbed," says Quad's director of imaging, Tom Frankowski. For example, an appale looks red because it absorbs blue and green wavelengths, but reflects the red ones to our eyes.

Red, blue, and green pigments are unusual for having this property--they completely absorb two of the primary colors while reflecting only one. That's why they are no good for mixing with one another. If you overlapped dots of blue and red ink, for example, each would absorb the wavelengths that the other one reflects. The result would be that all the wavelengths are absorbed; there'd be nothing left to see but black.

Yellow, cyan, and magenta pigments, on the other hand, each reflect two of the primary colors of light, in exactly equal proportions. Cyan, for example, absorbs red wavelengths, but reflects blue and green ones. So these primary pigments reflect more wavelengths that can be mixed in our eyes. Together they allow us to see some 2,000 printed colors--a mere 0.1 percent of the colors our eyes can detect, but enough to trick our brains into thinking we are seeing a full spectrum.

TO THE PRESSES

In modern printing, a machine called a scanner is programmed to determine which parts of a picture should be printed in each of these three primary pigments (see diagram, p. 11), as well as where black should go to add contrast. The Scanner also calculates how big or small the dots of each color ink should be. Big dots mean a solid blanket of color. Smaller onces allow for lots of space in between so that either the white paper or one of the other color inks can show through. That's how you get different hues, or what we call colors, and values, or gradations of color from light to dark.

The Scanner stores all of this iformation in computer files, which are then used to make the printing press plates. The dot pattern for each printing color is transferred to a plate, which is then mounted on a separate printing unit of the press (see diagram, p. 10).

When everything is ready, the machinery whirs, the paper rolls, the colors are printed in sequence--yellow, magenta, cyan, black. Giant heaters dry the ink and ... the colors of Science World come to life.