Understanding Process Color
Color images can be produced in two ways, depending on whether the image is being produced by light or by paints. If the image is being created by light — for example, the image you see on your TV or computer monitor — it is called the RGB color. If the image is being created by mixing paints onto a physical object — for example, applying ink to paper — it is called CMYK or process color.
RGB Color
The RGB color model is named for the three primary colors of light that can combine in different ways to produce most of the visual spectrum. These colors are red, green, and blue. Mixing all of these colors of light together at 100 percent intensity results in white. For this reason, RGB color is sometimes called additive color. The RGB color mode should be used only for an image that will be displayed on TV or the Internet.
CMYK Color
The CMYK color model is named for the four inks that can be combined in different ways to produce much of the visual spectrum. These colors are cyan, magenta, yellow, and black. (Black is abbreviated as “K” to avoid confusing it with “blue.”) Mixing cyan, magenta, and yellow together at 100 percent intensity yields black (or very close to it). For that reason, CMYK color is also referred to as subtractive color.
Cyan is often used to strengthen black ink. In other words, deep black is often created by adding cyan. In earlier comic books, this procedure was often done for characters' hair. The cyan would sometimes show through in a highlight area, giving the character a streak of cyan running through his or her otherwise jet-black hair.
Process Printing
All printing uses the CMYK color model. In the print industry, it's referred to as using process color. Preparing images for process printing requires an awareness of the limitations of the CMYK color mode. The spectrum produced by CMYK color is smaller than that of the RGB mode.
For that reason, your image should always be converted to CMYK before it is sent to the printer. If it is not, you could be producing colors that look fine on your computer screen (an RGB medium) but are unable to be printed. It is best to work only in CMYK unless you are going to be using some of Photoshop's special filters that operate only in the RGB mode. It is not wise to switch back and forth between CMYK and RGB as you refine your image, as the colors will become gradually duller due to the repeated conversions.
Building Color in CMYK Mode
Many people get confused when trying to mix CMYK color. In elementary school, students learn that the primary colors are red, blue, and yellow, and that all colors can be created by combining these three. And that's true, to a point. The problem is that “red” really means magenta, and “blue,” cyan.
Therefore, it is helpful to learn the CMYK makeup for some simple colors. Once you get the hang of CMYK color, it will be easy to manipulate the levels of the four inks to get any color you wish. Until then, use this chart to get started:
To get less intense colors, simply reduce the percentages of the inks proportionately. For example, to get a light blue, cut the intensity of the inks in half: 50 percent cyan and 25 percent magenta. To get a lighter blue, reduce each percentage to a quarter of the original value: 25 percent cyan and 13 percent magenta.
Where can I see process printing in action?
Look at the photos and graphics (especially the Sunday funnies) in your local newspaper through a magnifying glass. Since most newspapers print at a relatively low resolution (200 dpi), you can see the interplay between the inks with a magnifying glass.
