An Overview of Color Management

Maintaining calibrated displays and printers is essential to good color management. Every display and printer is unique. As these devices age, environmental conditions, system configurations, and changes in materials such as inks and paper affect the devices’ ability to reproduce color. Changes in the way a device reproduces color over time are known as drift. Maintaining good color management ensures that when you make adjustments to the colors in your images in Aperture, those colors are faithfully reproduced on your display screen and on the printed page.

What Is a Device’s Gamut?

The range of colors an individual color device is capable of reproducing is known as its gamut. Because of the differences in gamuts between devices, such as displays and printers, these devices are incapable of reproducing exactly the same range of colors. In fact, two displays of the same model made by the same manufacturer have distinct gamuts. Ink types and paper stock can also affect a printer’s gamut. Likewise, the age of a display and how frequently it’s used can affect its gamut.

Displays and printers cannot reproduce the same colors consistently when their gamuts don’t overlap. For example, the colors shown on a display are brighter and more saturated than are those produced by a printer. The illustrations below show representations of the range of color and brightness values each device is capable of displaying. If you superimpose the printer’s gamut on the display’s gamut, some of the display’s colors fall outside the range of the printer’s gamut. The printer is incapable of reproducing the full range of colors in the image displayed onscreen because of the printer’s smaller gamut. Color values that are contingent upon the ability of a device to reproduce color are known as device dependent.

Figure. Comparison of the shape of a display's larger gamut to a printer's smaller gamut.

What Is a Color Space?

When compared to the full spectrum of light, the gamut of a display or printer is relatively narrow. Because of the small gamuts of the devices, mathematical models are used to simulate the full spectrum of light within the gamuts of the devices. These models are known as color spaces.

Color spaces in which the interpretation of a color is not dependent on a specific device are known as device independent. The Commission Internationale de l’Eclairage (CIE) was established in 1931 to create standards for a series of color spaces representing the visible spectrum. The CIE color spaces, CIE XYZ and CIE Lab, are found in ColorSync Utility. As technology evolved, new color spaces were created for RGB and CMYK color.

Device-independent color spaces are used by ColorSync Utility, Aperture, and other color management systems to transfer and transform color data from one device to another. Color from one device-dependent color space, such as a display, is translated to a device-independent color space, such as sRGB, and then translated to another device-dependent color space, such as a printer. The independent color space acts as an objective interpreter, ensuring that the color data is accurately passed on to the next device.

Understanding ColorSync Utility

ColorSync Utility is the color management system used by Mac OS X. ColorSync is completely integrated with Mac OS X and available to all native Mac OS X applications, including Aperture. ColorSync is used to manage accurate color, from image acquisition to image manipulation and display to publishing. ColorSync is used consistently by all devices and applications in your workflow.

What Is a Device Profile?

ColorSync and other color management systems use device profiles to identify and transfer color data from one device-dependent color space, such as a camera, to another device-dependent color space, such as a printer. Device profiles contain data about the unique color characteristics of a device. A device’s profile includes information about its gamut, color space, colorants, and modes of operation.

Many types of hardware and software have generic ICC profiles available in ColorSync Utility. You can also use ColorSync Utility and a color measurement device, such as a spectrophotometer, to accurately create your own custom device profile. When you profile a color device, an ICC profile is created and placed in /Users/username/Library/ColorSync/Profiles/.

Figure. Custom device profile selected in the Profiles window.

Once your display and printer have up-to-date custom profiles, you can begin to make accurate color adjustments to your digital images in Aperture. Aperture uses the ColorSync CMM, or color matching method, to translate and transfer the color data from your camera to your display and then to your printer. Although the gamuts of the devices are very different, ColorSync knows the exact parameters of their gamuts because of their custom profiles. The ColorSync CMM allows you to preview how the color in an image changes when you make color adjustments in Aperture. As long as you have current profiles of your display and printer, the printed image will closely match the image on the screen.