Color Essentials | Real World Adobe Creative Suite 2

One of the problems we have found in trying to explain colors, color theory, and color management is that most of our students are designers who tuned out in science classes as soon as the teacher started talking about these (and probably other) topics. They thought, "Hey, I'm going to be an artist/designer. Why do I need to learn any of this stuff?"

Well, we're sorry to tell you, kids, but if you don't understand the science of color, or at least the basic essentials of the science, you're not going to understand much about colors and color management. So, at the risk of turning you back into a surly high-school student, here are some of the essential concepts you need to understand in order to work with color.

Color Theory

All color starts with light. If you sit in at the bottom of a cave that's been totally sealed off from any light source and look around, you're not going to see any colors. The absence of light means the absence of colors. Now, let's bring you back up outside the cave, and have you look at an apple. The skin of the apple looks red. But is that red really red? Bring the apple into your kitchen and the fluorescent lights will change the appearance of the red. Put the apple on a table lit by candles, and the red will change again. Wherever you are, the color of the light affects the color of the apple.

Our color guys describe this process in much greater detail. For now, what you need to know is that color is described as light bouncing off an object and then being viewed by an observer. However, it's not just the light affects the color; so does the type of object.

A wax coating on an apple will change the color of the apple. An apple made out of clay and painted red will have a different color. A plastic, toy apple will appear different. An apple printed on a T-shirt will look different from an apple printed on paper even if the exact same inks are used. In these cases, the object itself influences the perception of the color.

Finally, the type of observer is also an important factor. People view colors differently than animals. So what you see as red may look very different to your dog or cat. Some people (mostly men) have color blindness that causes them not to react to colors the same way as others do.

Types of Colors

There are two basic types of colors. Additive colors are the colors that are created from light. Although the actual light spectrum has six color categories (reds, oranges, yellows, greens, blues, and violets), there are three primary additive colors: red, green, and blue.

A good way to understand additive colors is to imagine three spotlights, each with a colored lens one red, one green, and one blue. When the three spotlights are aimed at a wall, the area where all three overlap will be white. The three colors added together create white. That's why they are called additive colors (Figure 10-6; see the color plates for the color version of this diagram.)

Figure 10-6. How the additive colors of light combine. (See the color version on page C-1 of the Color Insert.)

Computer monitors and television sets are examples of additive colors. Red, green, and blue combine to make all the colors on the screen.

Subtractive colors (also called process colors) are the colors in inks, paint, and other physical elements. They are called subtractive because as light hits the color, the color is subtracted from the original white source. The three subtractive primary colors are blue, red, and yellow. However, for the purpose of printing, the red color is described as magenta. The blue is described as cyan. And the yellow is described as, well, yellow.

As the theory goes, if you pour red paint into blue and then the blue and red into yellow, you get black. The black is the what's left when you take away all the white (Figure 10-7; see the Color Insert for the color version of this diagram).

Figure 10-7. How the subtractive colors of inks combine. (See the color version on page C-1 of the Color Insert.)

That's just the theory, though. In reality, a fourth color, black, is added to the three additive colors. (See the sidebar "Why Does Printing Use a Fourth Color?" for an explanation of this fourth color.)

Color Glossary

It's possible, as we go through the rest of this chapter, that we will use terms with which you may not be familiar. So, here's a brief glossary of color-related terms:

Blend: Term used to describe the effect when one object changes from one color or shape into another. Illustrator allows you to create blends that can be color or shape changes. The other CS2 applications use gradients to blend one color to another.

Brightness: Amount of light intensity. Lower the brightness and you lower the light.

CMYK: Abbreviation for the four inks used in process color printing: cyan, magenta, yellow, and black. A color of 20c, 40m, 0y, 10k represents a tint of 20% cyan, 40% magenta, 0% yellow, and 10% black. A CMYK image in Photoshop consists of four channels: Cyan, Magenta, Yellow, and Black.

Color space: A way of representing color using a set of three or more numbers. For example, one type of color space is the RGB space of a particular monitor.

Coated paper: Paper that has clay or another type of coating applied to one or both sides. Coated paper generally produces brighter images and colors.

Gamma curve: Describes how the middle tones of images appear. Changing the value of the gamma affects middle tones while leaving the lightest and darkest pixels of the image unaltered.

Gamut: The range of colors that can be reproduced by a specific media or device. A computer monitor is said to have a bigger color gamut than the colors in four-color printing. The term out-of-gamut describes those colors that can be seen on a monitor, but will appear different when printed using process inks.

Gradient: A blend that is created electronically with the software rather than by manually blending objects. Gradients are categorized by their shape: A gradient that changes color along a line is called linear. A gradient that moves out as a circle from a center is called radial.

Halftoning: A printing method used to create tones and tints by applying a grid pattern (also called a screen) of dots of different sizes and shapes. (See "Printing Basics" in Chapter 16, "Preflighting and Printing.")

Hue: A wavelength of color within the optical spectrum, or visible spectrum, of light. Thus, yellow is the hue of a banana. Green is the hue of a leaf.

HSB: The description of RGB colors that have been defined using their hue, saturation, and brightness.

Knockout: Term used to describe how one color is printed when another object, with a different color, is positioned underneath. The top color is said to knock out the bottom color when the two colors do not mix together. The shape of the top object pokes a hole in any objects underneath. The default setting for objects is to knock out.

Lab: (also known as L*a*b*) A way of defining colors, useful for color management, that uses lightness (L), red-green values (a), and blue-yellow values (b). Lab color is the intermediate color mode used when Photoshop converts one color to another.

Overprinting: Term used when one object does not knock out the color below it, but allows the inks to merge together. If a yellow object is set to overprint a blue object, the area where they overlap will print as green.

Process color: Describes the four-color printing process that uses patterns of cyan, magenta, yellow, and black inks to print images and colors.

Profiles: Software files that contain the information to convert colors into or out of a color space (see the definition above). For instance, a profile can be used to convert an image into a monitor color space or a printing press color space.

RGB: The description of colors created using red, green, and blue light. Monitors use RGB colors. An RGB image in Photoshop consists of three channels: Red, Green, and Blue.

Registration: A color that prints on all the plates of a document (meaning the four process colors as well as any spot colors in the document). The registration color is usually applied to printing elements such as crop marks, fold marks, and printer notes. It should never be used for artwork.

Rich black: In process printing, describes a combination of black plus any of the other process inks. The recipes for rich black are varied, but a generally accepted one is 40c, 40m, 20y, 100k.

Saturation: The intensity of the hue. The higher the saturation, the more of the hue is visible. As you lower the saturation, you add white to the hue.

Screen angles: The direction for the dot pattern of a color, used when printing with halftones. When two colors are combined to create a new color, each color has its own screen angle. If the screen angles for each color are set at the same angle, unacceptable patterns (called moiré patterns) may appear within the image.

Screens: The pattern of lines, dots, or other shapes used to print lighter shades of a color. A 25% screen indicates that the dot pattern covers only 25% of the area with that color.

Spot colors: Inks that are not based on one of the four process colors, and are printed on their own plate. Spot colors are used to match a color exactly (as for a particular corporate logo), to create a special effect (such as with a metallic ink), or to add an inexpensive, second color to black.

Tint: Term applied to screens of a specific color. Although usually used only for spot colors, it is possible to tint a process-color mixture.

Trapping: Technique used to compensate for incorrect registration of colors on a printing press. Most print shops recommend that you not apply trapping to documents manually. Instead, you should let the print shop handle the trapping electronically.

Uncoated paper: Paper that does not have a coating applied for smoothness. Uncoated paper displays colors differently than the same paper that has been coated.

Web colors: Colors defined using the hexadecimal system (which combines the numbers zero through nine and the letters A through F).

Web-safe colors: The 216 colors that can be viewed, without any dithering, on both Macintosh and Windows monitors that are set to display only 256 colors. Because so many users now have monitors that display thousands and millions of colors, there is much less need to restrict web pages to web-safe colors.

Why Does Printing Use a Fourth Color?

If the three subtractive colors create black, then why do print shops add a fourth color, black, to a printing press? The reason is that the theory of colors is different from practice. In theory the three colors create black. In practice, impurities in the colors create only a very muddy brown.

So the printing industry adds a fourth, key color black to ensure that blacks look their blackest. The key color is why the black plate is described as K in CMYK.