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In digital imaging systems, color management is the controlled conversion between the Color representations of various devices, such as Image Scanner s, Digital Camera s, monitors, TV screens, film printers, Computer Printer s, offset presses, and corresponding media. The primary goal of color management is to obtain a good match across color devices; for example, a video which should appear the same color on a computer LCD Monitor , a plasma TV screen, and on a printed frame of video. Color management helps to achieve the same appearance on all of these devices, provided the devices are capable of delivering the needed color intensities. CONCEPTS Various concepts and components are needed in a color management system: Characterization In order to describe the behavior of the various output devices, they must be compared (calibrated) in relation to a standard Color Space . Often a step called linearization is performed first, in order to get the most out of limited 8-bit color paths. Instruments used for measuring device colors include Colorimeter s and spectrophotometers. As an intermediate result, the device Gamut is described in the form of scattered measurement data. The measurement data (CGATS) is often not usable immediately. Such data need to be prepared for high speed conversions of the actual image data. The transformation of the scattered measurement data into a more regular form, usable by the application, is called profiling. Profiling is a complex mathematical process. After the profiling is finished, an idealized color description of the device is created. This description is called a profile. Flexibility Transforming profiled color information to different output devices is achieved by referencing the profile data into a standard color space. It is easy to convert colors from one device to a selected standard, and from that color space to the colors of another device. By ensuring that the reference color space covers the many possible colors that humans can see, this concept allows one to exchange colors between many different color output devices. Communicating diversity Image formats themselves (such as JPEG and TIFF ) may contain embedded Color Profiles , but are not required to do so by the image format. The International Color Consortium standard was created to bring various developers and manufacturers together. The ICC standard permits the exchange of output device characteristics and color spaces in the form of Metadata . This allows the embedding of color profiles into images as well as storing them in a database or a profile directory. Color space consistency Editing spaces (better known as working spaces) are a valuable concept that facilitates good results while compositing and manipulating images. They behave differently from most output device color spaces. They must be consistent regarding gray editing and color arrangement. For instance after brightening an image a gray should not become greenish. Most often such editing color spaces are described in simple mathematical formulas, such as SRGB or Adobe RGB . Gamut mapping Since different devices don't have the same Gamut , they need some rearrangement near the borders of the gamut. Some colors need to be shifted to the inside of the gamut as they otherwise cannot be represented on the output device and would simply be clipped. For instance to print a mostly saturated blue from a monitor to paper with a typical CMYK printer will surely fail. The paper blue will not be that saturated. Conversely, the bright cyan of an inkjet printer cannot be easily presented on an average computer monitor. The color management system can utilize various methods to achieve pleasant results and give experienced users control of the gamut mapping behavior. IMPLEMENTATIONS Parts of this technology are implemented in the Operating System (OS), helper libraries, the application, and devices. The concept for color management (known as ICM) in Microsoft Windows and Microsoft Office products is that every driver for an input device makes a color transformation from the color space of the device to sRGB. For the output device or the monitor, the driver has to make a color transformation from SRGB to the color space of the output device. This kind of implementation of color management is very user-friendly, because there is no need for any configuration. However, the quality of the results depends entirely on the quality of the color transformations, which are part of the drivers. A more open-concept, platform-independent view of color management is the use of an ICC-compatible color management system. The International Color Consortium (ICC) is an industry consortium which has defined an open standard for a Color Matching Module (CMM) at the OS level, and color profiles (ICC profiles) for the devices and working space. Beginning with Windows Vista , color management in Windows will be handled at the OS level through an ICC V4-compatible color management standard and API known as Windows Color System . Apple's Mac OS X and the classic Mac OS have long been capable of such color management which is called ColorSync . Another ICC concept is to make Color Profiles a part of file formats like TIFF , JPEG , PNG , EPS , PDF , and SVG . The Linux operating system uses ICC profiles, but support for Color Management On This Platform is still quite nascent, with only a handful of applications supporting it including Scribus and development versions of The Gimp . Besides ICC and WWW style color management, a lot of other color management approaches exist, partly due to history and partly because of other needs than the ICC standard covers. Particularly in the printing industry, in broadcasting and in film studios there are diverging demands and solutions. Color matching method is a software algorithm that adjusts the numerical values that get sent to, or received from, different devices so that the perceived color they produce remains consistent. The key issue here is how to deal with a color that cannot be reproduced on a certain device in order to show it through a different device as if it were visually the same color, just as when the reproducible color range between color transparencies and printed matters are different. There is no common method for this process, and the performance depends on the capability of each color matching method. PROBLEMS WITH COLOR MANAGEMENT
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EXTERNAL LINKS More information about color management for software developers can be found here: Standards
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