Color Management 101
Color management is the term used to describe an integrated system of computer hardware, software and workflow techniques all working together to translate color from one device to another in a controlled way. Color management is of great importance in graphic design; if you want your designs to look their best you should follow a color-managed workflow.
Gamut: Range of Colors Available
Various devices (monitors, printers, cameras, scanners, etc.) all handle color differently. Each device has its own characteristics when it comes to rendering color, and each has a limited range of colors it can reproduce. No device can reproduce all colors and all devices reproduce color differently. With any given image or design file, devices will interpret the color numbers in different ways, because of variations in the type of device and the colors model they use (red/green/blue; cyan/magenta/yellow/black, etc.) The range of colors that a device can reproduce (or that a digital file contains) is called the color gamut. A large gamut contains many possible colors and a small gamut contains relatively few colors.
Enter the CMS
The Color Management System (CMS) on your computer controls how colors are translated from one device to another. The CMS on Mac is called ColorSync; on Windows 7 it’s Windows Color Management. Both operating systems handle color management automatically. However, different programs, such as Photoshop, InDesign, etc., have their own controls for color management, and some programs—including most web browsers—do not use color management at all.
ICC Profiles: Source and Destination
The CMS translates color from one device to another with profiles, often referred to as ICC profiles. (ICC stands for International Color Consortium; look them up at www.color.org.) A profile describes the color gamut of a device or an image file. Profiles are stored in specific places within your operating system so they are made available to any program using the CMS. The CMS processes the source color values using the numbers in the profile to create the optimum values for the destination. For example, an image file in the Adobe RGB color space would be the source and an Epson printer would be the destination.
Out-of-gamut colors are those values present in the source but that do not exist in the destination. For example, with their limited gamut, many color printers and offset printing presses will have difficulty reproducing bright shades of blue.
The method the CMS uses to handle out-of-gamut colors is the rendering intent. The two most commonly used rendering intents are Perceptual and Relative Colorimetric. Perceptual compresses the gamut of the source to fit into the destination, remapping all the colors to preserve their visual appearance as perceived by the human eye. Relative Colorimetric keeps all the in-gamut colors unchanged and clips the out-of-gamut colors to the closest possible match within the destination gamut. Perceptual can often give the most natural rendering, but Relative Colorimetric is numerically more accurate. In prepress and proofing, you might use other rendering intents such as Absolute Colorimetric.
Calibrate and Profile Your Display
By far, the most important step in managing the color in your graphic design workflow is to have your monitor calibrated and profiled. You need to use the correct monitor profile to view accurate color. Most monitors come with a default profile, which you can specify in the Display system settings. You can either use the profile provided by the display manufacturer or make custom profiles yourself, using specialized hardware and software such as the X-Rite ColorMunki and i1 systems. Never use Adobe RGB, sRGB or ProPhoto as your display profile—these are intended only as working spaces for digital files. Always use a dedicated monitor profile.
Embed Profiles in Image and Layout Files
A working color space defines the available gamut for an image file. The most common RGB working spaces are sRGB, Adobe RGB (1998) and ProPhoto. The provided screen capture shows the Apple ColorSync Utility with the Adobe RGB (1998) profile loaded. Every image file should include an embedded profile that defines the working color space—this tells the CMS how to interpret the colors for that image. When you save image files, most often you should embed the working profile, so that later in the workflow all the devices will recognize the color space and handle the color translations correctly. Whether you’re working in RGB or CMYK, you should always embed the profile when you save files.
Working with Vendors
When sending an image to a print shop, prepress house, photo lab or other vendor, you need to know how your file will be processed. Ask them if there is a specific color space that they want the file saved in. Find out if the vendor can provide a profile for the equipment they will be using. When you’re working with outside vendors, good communication is essential to reproducing color accurately.
Take Control Over Your Color
In graphic design, working with color is one of the most common tasks. You must be in control over the colors you specify and also be sure how those colors will be translated further in the production workflow. Using a good quality, calibrated display is an essential aspect of proper color management. You should also learn about the color management settings in the software you use. These topics and more will be covered in future articles.