Image Color Matching in Windows 2000

By Brien M. Posey | Jan 17, 2001 | Print this Page
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If you create a Web page that contains images, you probably take for granted the idea that the images will appear the same to everyone. Sure, some people will have their video cards set to different resolutions or numbers of colors, but on comparable systems, the images should look the same. Although this idea sounds simple, it really isn't.

You've probably noticed that during the Windows Setup process, Windows attempts to determine the exact make and model of your monitor. The reason for this detection process is that every brand of monitor works a little differently. If you view an image that has with just a few colors, such as a 16- or 256-color image, you'd probably never notice these subtle differences. However, if you view a high-resolution photograph that contains lots of colors, the differences quickly become apparent.

Image Color Management

This is where Image Color Management (ICM) 2.0 comes in. ICM 2.0 is a Windows 2000 component; its job is to make sure that an image looks the same on every system. It accomplishes this task by looking at the profiles for each individual type of monitor. By knowing exactly how an individual monitor will display a known color, ICM can alter the color so that it's displayed correctly on that monitor.

For example, suppose ICM knew that a particular monitor displays the color blue just a bit too dark. ICM could alter the way that images containing blue are displayed, so that the color blue is displayed accurately in spite of the monitor's inherent flaws.

Beyond Monitors

As cool as ICM is, its functionality doesn't stop with monitors. ICM performs the same type of task on a wide variety of other devices, such as scanners, digital cameras, and printers. ICM maintains a color profile for each type of input device. Because the specific color inaccuracies are known for each device, ICM can correct the images as they're fed into the computer. Likewise, because ICM knows about color inaccuracies associated with printers, it can intervene to make sure images are printed in accurate colors.

Because ICM relies so heavily on device profiles, you may wonder what happens when a device has no profile. Usually, ICM is used in situations with both a source and a destination device. For example, a scanner might be the source, and the monitor might be the destination. If either device contains a color profile, that color profile is used--even if the other device doesn't have a profile. When a device doesn't have a profile, ICM uses a built-in color profile called sRGB in place of the missing device-specific profile. //

Brien M. Posey is an MCSE who works as a freelance writer. His past experience includes working as the director of information systems for a national chain of health care facilities and as a network engineer for the Department of Defense. Because of the extremely high volume of e-mail that Brien receives, it's impossible for him to respond to every message, although he does read them all.