WHEN PREPARING PRINT AND ONLINE MEDIA, instructional designers often use the same color graphics for both. Have you been in a situation where you were asked to prepare a print version of documentation and a version for access on your website as well? Usually, you can re-purpose or convert the text easily, but what about the graphics. How do the colors translate? In order to understand what happens to the color in your graphics, you need to understand how color is defined on a computer and how color changes as it goes from device to device. In studying color management, we will focus on the topics of color models, color gamuts and color mapping.

There are two basic color models used to define color. The first is RGB, which stands for Red, Green, and Blue, is used to define color displayed on a monitor. The second is CMYK, which stands for Cyan, Magenta, Yellow, and Black (the B was already taken by Blue) and is used to define colors printed on paper. The range of colors that each medium can reproduce, monitor and print, are not the same so this is where the challenge presents itself.

Color on a monitor is produced with light-emitting phosphors. For each pixel on your screen there is a set of 3 phosphors (red, green, blue). The intensity of each (lightness/darkness) and the balance of each (saturation) produce different colors. 

RGB Color Model

If the light from all three colors is at 100% and you combine them, you will get white light. This is known as an additive color system.

Color on paper is produced by the light-absorbing character of inks printed on the paper. When light strikes translucent inks, part of the spectrum of colors is absorbed and part is reflected back and this is what we see.

CMY Color Model

Theoretically, if you combine 100% of cyan, magenta, and yellow inks on paper, it would absorb all the light and display or black. Actually the three inks produce a very muddy black, so printers add a separate black ink (K) to make it solid. CMYK is known as a subtractive color system.

Notice that the two color spaces complement each other.

RGB and CMYK each produce a different gamut, or range of colors. Because RGB uses light to produce its colors, it is capable of producing much brighter colors which inks cannot reproduce. Correspondingly, inks used to print colors can produce some wonderful pastels that you just can’t match on a computer screen. Although all color gamuts overlay, they don’t match exactly.

The human eye can see a wide range of colors. As this graphic shows, the range of colors that can be reproduced using the RGB or CMYK color models is much more limited. 

CIE (Commission Internationale d'Eclairage) color models.

Notice that the monitor's shape is similar to the eye's. It just can't reproduce as much saturation. That's because the eye is an RGB sensitive device.

To further complicate the situation, not all RGB and CMYK gamuts are alike. Different monitors, scanners, and computers vary in how they reproduce color. Have you ever sat next to someone in a computer class and noticed their monitor’s color looked a whole lot different than yours? The way individual devices reproduce color defines their color space.

Professional computer graphics software use a color management system(CMS) to compensate for all these differences. The CMS translates colors from the color space of one device into a device-independent color space(an objective reference). This color space is then translated to another device’s color space by a process called color mapping. In this way, you can be assured that your color will be as accurate as possible as it moves from screen to print or vice versa.

Additional information on color is available in these other EET articles:

Choosing a color palette
Principles of using color

Use of color in graphic representation

Visit these websites for more information on color and color management:

Adobe Web Site - Technical Guides on Color
International Color Consortium

Pantone Web Site - Color Fundamentals

Sarah Ryan-Roberts, SDSU student, Educational Technology Department