The Critically Important Color and Gamma Calibration Article - International Color Consortium (ICC)
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In 1993, the International Color Consortium (ICC)—a group of companies recognized as leaders in the fields of electronic publishing, software development, and digital prepress—formed a committee to establish standards for electronic color publishing. The ICC based its standardized color information on the CIELAB color space, and developed device profiles that would easily transfer color information from one device to another and from one computing platform to another.
Here is the problem the ICC tackled: Each printing device, scanner, digital camera, and monitor has its own way of rendering a color (that is, assigning a meaning to a color). This meaning is called the device's color space.
Monitors, for example, specify colors as values of red, green, and blue (RGB). The values R:100, G:20, B:30 specify a certain shade of red on a particular monitor. These values are said to be device-dependent; if these values are sent to a second monitor with different colored phosphors, a different color red will be displayed. If they are sent to a printer that describes colors as percentages of cyan, magenta, yellow, and black (CMYK), yet another different red will be printed.
Which is the correct color? The color seen on the first monitor? The color seen on the second monitor? Or the color printed on the printer?
Photoshop CS Color Working Spaces
Fast forward to today. To enable Photoshop to provide uniform ways of describing color space, Adobe needed to offer several different standard color working spaces. Thanks to the foundation laid by the CIE and the ICC, Adobe was able to do so. For RGB images Photoshop offers sRGB, Adobe RGB 1998, Apple RGB, and Colormatch RGB working spaces. For CMYK working spaces, Photoshop offers US Web Coated SWOP, US Web Uncoated, US Sheetfed Coated, US Sheetfed Uncoated, Japan Standard, Euroscale Uncoated, and Euroscale Coated.
Establishing these color working spaces wasn't enough. How could that information be exchanged between devices?
Enter ICC profiles.
ICC Profiles
ICC profiles are an essential element of the color management equation. Because no device can be brought into perfect calibration, and because no two devices—monitors, printers, or scanners—perform identically even if they are the same make and model, profiles are created to document the ways a specific device strays from the standard. What kind of documentation is this? Well...
The Adobe CMS uses ICC standard device profiles to ensure that colors are accurately converted across devices. Profiles are data files that record all the relevant information for a particular device, including its color space, capabilities, and limitations. Each profile relates a device's color space to the CIE-referenced color space. By doing so, a profile assigns an absolute meaning to each color that a device can produce.
When you transfer an image between two devices that have ICC profiles, a Color Management Module (CMM) compares the ICC profile of the source device (such as the monitor) with the ICC profile of the destination device (such as the printer) to create consistent color results. With the information contained in the ICC profile, the CMM transforms colors in image files to produce consistent color simulation on the monitor and the proofing device. For every RGB value in the monitor color space, for example, the color transformation produces a similar CMYK value in the printer's color space. If a color space specified on one device falls outside the color gamut of another device, the CMS may automatically reassign the actual values put out from the devices to preserve the relationship of colors from one device to another. The CMS in effect remaps colors that fall outside the other device's gamut, but...it does so in a way the human eye accepts.
Note - In Windows it's ICM
Because the Windows operating system had already assigned the ICC suffix to another system component, Windows refers to ICC profiles as ICM. The suffixes ICC and ICM are interchangeable in the language of CMS.
How do you get ICC profiles? Adobe and your operating system offer generic profiles for popular brands of monitors. Adobe also offers Adobe Gamma, which creates a custom ICC profile the Adobe CMS can use to understand how your monitor handles color. (Hang on. We cover Adobe Gamma next.)
Even if one of the generic profiles fits your monitor, we recommend that you create a custom ICC profile. It is not recommended (at least, not by us) to use preset monitor profiles. They are of little value, due to aging and varied viewing conditions of the devices that the profiles describe. Custom profiles are always better. After all, would you rather have a picture of an ideal family or a picture of your family?
Note - Profiling
When you create an ICC profile for your monitor, you are making a system-level adjustment. This means that any program that is color management–capable uses the ICC profile you've created for your monitor.
You can (and should) have multiple ICC profiles for printing devices—one profile for one specific working condition. But use only one profile at a time. Also, be careful that you are using the correct profile for the current condition. For example, you may have one profile for your inkjet printer that you use with the manufacturer's standard glossy paper, and another that you use with a third party's glossy paper.
In addition to performing regular calibration (hey, stuff ages) and profiling of the monitor, an artist should try to maintain consistent lighting conditions. The monitor needs to be calibrated and profiled at least once a month. Of all the devices that require ICC profiles, the monitor loses its calibration the quickest.
 This chapter is from Inside Photoshop CS, by Gary D. Bouton. (Sams, 2004, ISBN: 0672326442). Check it out at your favorite bookstore today. Buy this book now.
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