Color management: An overview
Although all color gamuts overlap, they don’t match exactly, which is why some colors on your monitor can’t be reproduced in print. The colors that can’t be reproduced in print are called out-of-gamut colors, because they are outside the spectrum of printable colors. For example, you can create a large percentage of colors in the visible spectrum using programs such as Photoshop, Illustrator, and InDesign, but you can reproduce only a subset of those colors on a desktop printer. The printer has a smaller color space or gamut (the range of colors that can be displayed or printed) than the application that created the color.
Visible spectrum containing millions of colors (far left) compared with color gamuts of various devices and documents
To compensate for these differences and to ensure the closest match between on-screen colors and printed colors, applications use a color management system (CMS). Using a color management engine, the CMS translates colors from the color space of one device into a device-independent color space, such as CIE (Commission Internationale d’Eclairage) LAB. From the device-independent color space, the CMS fits that color information to another device’s color space by a process called color mapping, or gamut mapping. The CMS makes any adjustments necessary to represent the color consistently among devices.
A CMS uses three components to map colors across devices:
ICC profiles that define the color characteristics of particular devices and documents.
A color management engine that translates colors from one device’s color space to another according to a rendering intent, or translation method.
A. Scanners and software applications create color documents. Users choose document’s working color space. B. ICC source profiles describe document color spaces. C. A color management engine uses ICC source profiles to map document colors to a device-independent color space through supporting applications. D. The color management engine maps document colors from the device-independent color space to output-device color spaces using destination profiles.
About the device-independent color space
To successfully compare gamuts and make adjustments, a color management system must use a reference color space—an objective way of defining color. Most CMSs use the CIE LAB color model, which exists independently of any device and is big enough to reproduce any color visible to the human eye. For this reason, CIE LAB is considered device-independent.
About ICC profiles
An ICC profile describes how a particular device or standard reproduces color using a cross-platform standard defined by the International Color Consortium (ICC). ICC profiles ensure that images appear correctly in any ICC-compliant applications and on color devices. This is accomplished by embedding the profile information in the original file or assigning the profile in your application.
At a minimum, you must have one source profile for the device (scanner or digital camera, for example) or standard (SWOP or Adobe RGB, for example) used to create the color, and one destination profile for the device (monitor or contract proofing, for example) or standard (SWOP or TOYO, for example) that you will use to reproduce the color.
About color management engines
Sometimes called the color matching module (CMM), the color management engine interprets ICC profiles. Acting as a translator, the color management engine converts the out-of-gamut colors from the source device to the range of colors that can be produced by the destination device. The color management engine may be included with the CMS or may be a separate part of the operating system.
Translating to a gamut—particularly a smaller gamut—usually involves a compromise, so multiple translation methods are available. For example, a color translation method that preserves correct relationships among colors in a photograph will usually alter the colors in a logo. Color management engines provide a choice of translation methods, known as rendering intents, so that you can apply a method appropriate to the intended use of a color graphic. Examples of common rendering intents include Perceptual (Images) for preserving color relationships the way the eye does, Saturation (Graphics) for preserving vivid colors at the expense of color accuracy, and Relative and Absolute Colorimetric for preserving color accuracy at the expense of color relationships.
Color management resources
You can find additional information on color management on the Web and in print. Here are a few resources:
On the Adobe Web site (www.adobe.com), search for color management or go directly to http://www.adobe.com/support/techguides/color/.
On the Apple® Web site (www.apple.com), search for ColorSync.
On the LinoColor Web site (www.linocolor.com), open the Color Manager Manual.
On the Agfa Web site (www.agfa.com), search for the publication The Secrets of Color Management.
On the ColorBlind Web site (www.color.com), click Color Resources.
At your local library or bookstore, look for GATF Practical Guide to Color Management, by Richard Adams and Joshua Weisberg (May 1998); ISBN 0883622025.
 | For information about setting up color management in Photoshop, see Photoshop 7.0 online Help. |