Chapter 27
Color for the Color Blind

Featuring

At our ongoing series of CorelDRAW seminars, we routinely ask the audience for a show of hands: “Do you think you have a good understanding of color publishing?” In a crowd of 100, it is unusual for more than a dozen to raise their hands. Despite the proliferation of color scanners and affordable desktop color printers, the realm of color publishing continues to give DRAW users a case of the heebie-jeebies (to use the technical term).

Don’t expect this chapter to be the ultimate treatise on working with color. Dozens of books dedicated to the subject are readily available to you from the usual sources. This chapter should serve as your launching pad. Once you’ve read it, you’ll be able to recognize the terms, understand the concepts, and above all, be able to translate it all into effective use of DRAW as your front end for color publishing projects.

Do You See the Light?

When creating the heaven and the earth in those first six days, God also created two ways that humans perceive light. We see light that is directly transmitted from a source (from the sun or a light bulb, for instance), and we see light that is reflected (from the moon, the clouds, the walls in your house, and the pages of this book). Why should you care about this self-evident fact? Because as a computer user, you deal with both types of light, so it’s important to understand how they are different.

Like the sun and a light bulb, your computer monitor is a light source, and the light it uses to display images is transmitted directly to your eyes. On the other hand, your computer produces a printed piece that reflects light but does not transmit it. This is a very important point that we will return to throughout this chapter.

You have probably heard these terms before—RGB and CMYK. They are the color models that most distinctly represent these two kinds of light.

The ABCs of RGB

So you’ve probably heard of RGB, and maybe you sort of know what it is—a way of defining colors—and that the initials stand for Red, Green, and Blue. (Maybe you’ve also heard the term “RGB monitor,” which is a bit superfluous, because there can be no other type of monitor than an RGB one.) Although most light sources in the physical world emit white light, which is made up of all the colors of the rainbow, the human eye perceives only red, green, and blue light. In other words, all the colors that the human eye can perceive are registered by the eye as combinations and varying intensities of these three colors. That’s why color monitors and TVs, which emit only red, green, and blue, can simulate the full spectrum.

Figure 27.1 shows a woman looking at a computer monitor. In this black-and-white drawing you can’t tell that she is seeing a monitor with a yellow screen, but she is (although it looks as if her eyes are closed, but we’ll overlook that). What forces are at work that cause “yellow” to register in her brain?

	NOTE Here we are faced with our annual frustration: how to present a chapter on color publishing in a book printed in black and white. Thank goodness for the companion page of the Sybex Web site—there you’ll find all relevant drawings, named according to their figure numbers. For instance, Figure 27.1 is file f2701.cdr at the Web page.

Like all color monitors and TVs, hers emits RGB light, which means little rays of red, green, and blue light emanate from the monitor. In fact, if you held a magnifying glass up to your own display, you would see hair-thin lines of red, green, and blue. In Figure 27.1, the monitor is emitting red and green light, the two colors that combine to produce yellow. Why yellow, you ask? Because that’s what red and green do. It would take too much time and ink to explain the science of RGB light, so let’s just accept the fact that when red and green light are combined, they form yellow.

FIGURE 27.1  This monitor is transmitting red and green light, and those two colors combine to form the yellow screen seen by the woman.

RGB is the most straightforward of the various color models, not only because it depicts the behavior of light in the real world, but also because it is easy for humans to visualize. Imagine a bunch of red, green, and blue flashlights shining in various directions in a darkened room. When the rays of light overlap, they form other colors. By varying the intensities of the rays (pretend you have very sophisticated flashlights), you can create all the colors that the human eye can perceive.

When combined at full intensity, red, green, and blue form white, although you might have been tempted to guess the opposite, remembering your crayon-drawing days when using all of your crayons at once gave you a nice black mess. But black is actually the absence of light—a point that is obvious to anyone who has walked into the coffee table in the middle of the night.

The RGB color model is called an additive model, because those three primary colors combined in various intensities produce the spectrum of visible colors.

Reflections on CMYK

You probably know that CMYK stands for Cyan, Magenta, Yellow, and Black (K for Black because B could also be for Blue). And you probably also know that those are the four ink colors used in conventional four-color printing. What you may not know is that CMYK is worlds apart from the RGB color model. RGB represents the transmission of colors, but CMYK represents the reflection of colors.

The light you see from a printed piece is reflected light. This book, for instance, is not a light source (although we hope it is illuminating); rather, the black ink on this page absorbs light and the white paper reflects light. Colored inks and papers each absorb some portions of the light striking the surface and reflect others, allowing you to see particular colors.

Figures 27.2 and 27.3 demonstrate the process of reflected light. In Figure 27.2, a man is looking down at a book illuminated by white light and he sees red. Why? What forces are at work here that cause him to see red?

FIGURE 27.2  Red, green, and blue rays of light are hitting this page. Why does this man see only red?

The page he is reading is not like a computer monitor—it transmits no light of its own. So to read the page, the first thing he needs is a light source. Like all white-light sources, his emits red, green, and blue rays of light. In Figure 27.2 the desk lamp is flooding the book with RGB light.

The question now becomes this: If the light hitting this page is full-spectrum white light, how come the only light that bounces off the page is red? What ink colors are present on the page to make this so? Figure 27.3 has the answer: yellow and magenta (best seen from f2703.cdr on the Web site). When the light hits this book, the yellow ink absorbs colors at the blue end of the spectrum. Why does this happen? Again, we could write another book entirely about this topic—it’s called the “subtractive” theory of color. That’s what yellow does—it absorbs blue light. And the magenta absorbs the green, because that’s what magenta does. So with all of the blue and green light absorbed by the ink on the page, the only color that reflects off the surface is the red.

FIGURE 27.3  The ink on the page absorbs most of the color spectrum, but allows the red to pass through and be reflected off the white paper.

This man sees red because the page contains yellow and magenta ink. Though you might be tempted to say that yellow and magenta combine to make red, that’s actually RGB-speak. Rather than combine, they each filter out one of the other two colors, resulting in red. It may seem like this is just a semantic distinction, but it helps to better digest the whole color thing when you think of CMYK inks in terms of what they take away, not what they add.

You don’t need to understand the intricacies of additive and subtractive color theories, but you should grasp the moral of this story so far: color from your monitor is totally different than color from a printed piece. We will return to that point later in this chapter.