What is a Color Management System

A color management system (CMS) is a set of program modules that mediate color translation between different devices. These modules are often part of a computer's operating system, and they are usually provided by software manufacturers. If an application is used to display, edit, or print a color image, it initiates the appropriate function(s), such as displaying an image or generating the correct ICC profile information, and then tells the CMS what function should be performed. The central part of the CMS is a color CMM = "color management module" or management module (CMM)* which performs the calculations needed to "color matching module" translate (transform) a color from color space A to color space B. Here's how it works:

1. First, the CMM translates the device-dependent color values in the image to the device-independent L*a*b* color space, using the description in the source ICC profile. This intermediate space is called the transfer color space or profile connection space (PCS).

2. Next, the L*a*b* values are translated to color values that will produce a color on the output device that is as close to the original color as possible. If the output device cannot produce the exact same color, the CMM will try to find the closest match. The best match is determined by a kind of translation intent (explained in section 3.3 on page 68), called the rendering intent.

The ICC profiles used in this schematic are actually simple translation tables. They support translation from device-dependent color values to device-independent color values, and vice-versa.

Photoshop and other applications that support color management embed the ICC profile data within the image file; this new file is called a tagged file or tagged image. When you pass the tagged image on, the profile information is passed on with it. You should be aware that not all image file formats support ICC profiles - TIFF and JPEG do, GIF doesn't. As you have probably noticed, GIF images have unacceptable color depth anyway.

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