Primary ColorsThe concept of primary colors is at the heart of much of the color work we do on computers. When we work with primary colors, we're talking about three colors that we can combine to make all the other colors. We can define colors by specifying varying proportions of primary colors, and we can color-correct images by adjusting the relationship of the primary colors. Ignoring for the moment which specific colors constitute the primaries, there are two fundamental principles of primary colors.They are the irreducible components of color.The primary colors, combined in varying proportions, can produce an entire spectrum of color. The secondary colors, by the way, are made by combining two primary colors and excluding the third. But we don't much care about that. It is important to note, though, that what makes the primary colors specialindeed what makes them primary colorsis human physiology rather than any special property inherent in those wavelengths of light. Additive and Subtractive ColorBefore becoming preoccupied with the behavior of spherical objects like apples, billiard balls, and planets, Sir Isaac Newton performed some experiments with light and prisms. He found that he could break white light down into red, green, and blue components, a fairly trivial phenomenon that had been known for centuries. His breakthrough was the discovery that he could reconstitute white light by recombining those red, green, and blue components. Red, green, and bluethe primary colors of lightare known as the additive primary colors because as you add color, the result becomes more white (the absence of colored light is black; see Figure 4-1). This is how computer monitors and televisions produce color. Figure 4-1. Additive and subtractive primariesAn Imperfect WorldA little while ago, we asked you to trust us on the subject of CMYK. Well, we just told you that combining cyan, magenta, and yellow would, in theory, produce black. In practice, however, it produces a muddy brown mess. Why? In the words of our friend and colleague Bob Schaffel, "God made RGB . . . man made CMYK." To that we add: "Who do you trust more?" Imperfect pigmentsIf we had perfect CMY pigments, we wouldn't have to add black (K) as a fourth color. But despite our best efforts, our cyan pigments always contain a little red, our magentas always contain a little green, and our yellows always contain a trace of blue. Moreover, there's a limit to the amount of ink we can apply to the paper without dissolving it. So when we print in color, we add black to help with the reproduction of dark colors and to achieve acceptable density on press. See Chapter 5, Color Settings, for more on this. Imperfect conversionsIf we only had to deal with CMY, life would be a lot simpler. However, a large part of the problem of reproducing color images in print is that scannerssince they deal with lightsee color in RGB, and we have to translate those values into CMYK to print them. Unfortunately, this conversion is a thorny one (see Chapter 5, Color Settings, for more on this subject). |