Color matching and gamma correction

Some designers and clients complain that graphics developed on one platform don't look the same on another. Find out how color matching and gamma correction can help.

By Paul Anderson

One problem with the RGB color model is that it measures color relative to the hardware being used at the time. A common complaint among designers—and their clients—is that graphics developed on one platform don't look the same on another. For example, an image that looks great on a PC may appear pale or washed out on a Macintosh.

The problem is that all monitors are not alike, and it goes deeper than ambient light or the brightness knob. The relation between RGB values and the actual color displayed on the screen is almost never linear. For example, a red channel set to 200 should theoretically be twice as bright as a red channel set to 100, but it usually isn't. And the actual relation, called gamma, varies from computer to computer, so even if one color matches on two computers, most other colors still won't.

The images below simulate the effects of two systems with different gamma values:

PC Macintosh

Color management is a problem with many computer peripherals. It takes built-in color matching (such as ColorSync on the Macintosh) or third-party products (such as the Pantone Matching System) to shepherd colors intact through digital cameras, scanners, and printers. But once an image is on the Web, your only worry is your users' monitors. The solution there is gamma correction. By including the intended gamma value with an image, you can leave it to individual users' rendering software to correct it relative to their monitor's color curve.

Unfortunately, popular image formats don't support gamma correction. For the most part, the Web has gotten by without gamma correction, but precise colors matter for online companies that want to sell merchandise such as clothing, cosmetics, and paint. And that was part of the impetus behind the Portable Network Graphics (PNG) format, which includes gamma values. The World Wide Web Consortium (W3C) published the final PNG specification back in 1996, but Web browsers and graphics applications have begun to support it only recently.

Paul Anderson is associate technical editor for CNET Builder.com. His responsibilities don't include handling graphics, so naturally, he handles them all the time.

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