Windows Color Management: Background and Resources
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Introduction
Digital media presents both consumer and professional users with challenges for getting consistent color from input devices such as camera and scanners to rendering devices such as displays and printers.
For example, a digital camera owner wants to transfer pictures to the PC for slide shows and to a printer for copies, with the color in each output matching the image from the source device. In the publishing industry, designers want identical color results when a clients print job is passed to the service bureau and then to the print shopand also want the image to look great when it is on the Internet.
Today, the standards-based color management capabilities of Windows XP, Windows 2000, and Windows Millennium Edition (Windows Me) operating systems offer sophisticated support that is equal to or better than any comparable computing platform.
Windows delivers color management benefits for end users throughout the production process: from image acquisition and editing, to display and print output. Microsoft also provides tools for developing and testing devices to help manufacturers take advantage of color management.
Microsoft Windows and color management
Windows XP, Windows 2000, Windows Me, and Windows 98 provide color management support.
ICC Profiles | Color profiles that comply with the International Color Consortium (ICC) Profile Format specification work in all of these versions, to support flexible, state-of-the-art color control |
sRGB Standard | The default color space is the IEC 61966-2-1 standardsRGB-compliant devices do not have to provide profiles or other support information to work well |
ICM 2.0 API | Software written with the Image Color Management (ICM) APIs runs in all these versions of Windows |
Color Test Kits | Microsoft-provided kits for color-capable devices help manufacturers validate capabilities in the development process |
Why Color Management Matters
To achieve color consistency, color processes must be managed with these considerations in mind:
| • | Compatibility. The process must ensure compatibility among different input and output devices, publishing and imaging software, and commercial publishing systems. Historically, the publishing industry has used proprietary systems that require all components to be designed and calibrated to work togetherwhich imposes constraints that arent workable in an open, heterogeneous PC-based computing environment. |
| • | Workflow. The process must ensure continuous workflow from input to display to output devices without intermediary image conversion or color correction. |
| • | Transparent, Predictable Color Reproduction. Color consistency must be maintained automatically by the hardware, operating system, and applications. Consistency must also be maintained across different software for scanning, editing, composition, proofing, and distribution. |
Color Management Challenges
"What you see is what you get" color results across scanners, monitors, applications, and printers have been difficult to achieve because of differences in how each defines the following aspects of color:
Illuminants and Colorants. Devices such as monitors and scanners use an "additive" color system based on red, green, and blue (RGB)starting with black and then adding red, green, or blue as needed to produce a specified color. Additive illuminants are the monitor phosphors and the light emitting component in scanners.
Other types of devices, such as printers, use the "subtractive" color system, typically using cyan, magenta, yellow, and black (CMYK)starting with white and subtracting RGB to produce colors and black. Subtractive illuminants are the ambient lighting environment.
Differences occur, therefore, in the color results on the different devices because, for example, the spectral transmission of the displays phosphors differ from the spectral reflectance of the printers cyan colorant.
However, other matching problems occur because colorants appear different in different viewing conditions, and different vendors use different colorants. So one CMYK printer will have one color cyan while another will use a different color cyan. When compared inside a room versus outside in the sunlight, the output might appear different in yet another way.
Device Gamuts. Each device produces a particular range of colors, known as the device gamut, as determined by the devices physical characteristics and ambient lighting. Therefore, colors may appear rich in a dimly lit room and washed out in a sun-lit room.
To compensate for differences in how different devices handle color, any color management technology must address elements such as the following:
| • | Color Space. Describes a set of colors and their relationships. The industry-standard color space sRGB is used as the default color space in Windows. Many device-dependent (and proprietary) color spaces have been defined in different industries. |
| • | Color Calibration. Ensures that the scanner, monitor, and printer correctly detect and output a variety of color factors such as density and luminance. |
| • | Color Characterization. Specifies the gamut and other factors that influence how a device reproduces color. |
| • | Gamuts. Varies on different input and output devices according to distinct factors: Printers - By each supported media and ink Monitors - By the phosphors used in the monitor and the type of display adapter Scanners - By whether flatbed or drum technology is used, the closed-circuit display (CCD) and light source, and the reflective or transparent media |
| • | Color Profiles. An industry-standard, cross-platform format for characterizing device color capabilities. Windows ICM 2.0 supports profiles that conform to the ICC profile specification. |
Windows Benefits for Users
The Windows color management capabilities allow users to choose the right solution for specific casesor be supplied with flexible defaults that meet most mass-market needs.
Benefits of Windows color management
By supporting industry standards, Windows ensures cross-platform compatibility and provides transparent ease-of-use for applications.
Graphics design and publishing professional |
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Business users |
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Consumers |
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ICC Profiles: Color Management for Professionals
ICC profiles are used to communicate through the rest of the color management system to ensure that colors are represented accurately to users, regardless of the device used for display or printing. ICC profiles for devices offer great flexibility and control, and can be used to describe the unique color management capabilities of a particular device.
To take advantage of ICC profiles in Windows, each device must have its ICC profile installed. This can occur automatically when the device is installed, or the user can use the Display Control Panel to associate a profile from the device manufacturer.
Developers can test color spaces, characterization factors, and device gamuts and then record the differences among them in the ICC profile for the device. This testing can be accomplished by one of many third-party software and hardware products available. For sRGB-compliant devices, the Windows default sRGB profile can be used.
Developers who are creating applications designed to portray colors accurately can use the ICM 2.0 API. The ICM 2.0 technology also supports alternate color management modules (CMMs) that transform color information between different color spaces, such as the RGB colors captured by the scanner to the different RGB values displayed on a monitor or sent to printers.
ICC Profile Format Specification
see the International Color Consortium web site at:
http://www.color.org/
SRGB Standard: Color Management for Consumers
Hewlett-Packard and Microsoft helped to develop and drive the sRGB color space as a published international standard (IEC 61966-2-1). In the most basic sense, when the operating system, devices, and applications support sRGB, the result is a simple, easy-to-use solution that works for many kinds of hardware and software that historically have been unable to represent color in a consistent manner without direct user intervention.
The sRGB color space offers these benefits:
| • | Eliminates the need for device-specific ICC profiles, a particular advantage for consumer applications |
| • | Enables an improved method for handling color in the operating system and on the Internet |
| • | Provides good-quality color representation on monitors, with minimum transmission and system overhead |
| • | Enables support with minimum cost to software and hardware vendors because it is based on the calibrated, colormetric RGB color space of high-definition television |
sRGB color management provides a simple, robust system in which device vendors and content creators are responsible for converting content into and out of sRGB prior to exchange. sRGB is the ideal color space for monitors because it assures a uniform tone, making it also ideal for display-centric solutions such as the Web.
Because sRGB is the only color space for multiple devices that is a published international standard, it is the best solution for exchange in multiple-media and multiple-device environments. This standard is being broadly adopted:
| • | Companies that have adopted it as a default include Adobe, the World Wide Web Consortium, Hewlett-Packard, Microsoft, Fuji, Sony, Mitsubishi, Barco, Agfa, and other vendors. |
| • | Epson and Hewlett-Packard have developed consumer printers that ensure very good color matches to sRGB from display to printer. |
| • | Content is broadly available in sRGBfor example, all consumer digital cameras convert JPEG content to sRGB prior to export. |
ICC Profiles vs. sRGB in Workflows
A workflow takes color images from inception to final output, and may involve many different devices.
sRGB and Workflows. The sRGB color space and workflow have proven very robust under differing input, viewing conditions, and calibration states. This is a significant advantage for applications such as e-commerce Web sites, where a consumer's purchase decision is based on an expectation of consistent color representation from display to printout to actual product.
sRGB was designed for the display color space, so it may have limitations in workflows that do not involve displays, such as scan-to-print or capture-to-print. Most consumer printers perform excellent gamut mapping to expand the sRGB space to fill their inkjet color gamut without sacrificing color fidelity.
ICC and Workflows. ICC color management workflows provide a flexible but complex system in which each device vendor or user must characterize the color of that device into an ICC profile, a standard format for expressing a devices color capabilities. ICC profiles provide a highly controlled, common color language among devices and complex workflows.
ICC profiles work best as a quality-control mechanism in homogeneous, high-volume workflows such as newspapers, or in custom workflows with a single-user system and an expert user. Because ICC requirements are not easily met in consumer applications, ICC workflows are not suitable in products targeted to the consumer market:
| • | Different tools for creating profiles for the same device create very different color results. |
| • | Different translation enginesalso called CMMscreate different results for the same profile pair. |
| • | Complex workflows require that every step of the process, from capture to output, maintain accurate profiles for each device and that all applications use ICC color management. For reliable results, the same profile-creation vendor and translation-engine vendor must be used throughout the process. |
| • | ICC workflows do not readily tolerate variances from process requirements. |
Color Management-Capable Application Challenges
Applications that implement color management schemes often create problems such as:
| • | Writing to a different, proprietary color system |
| • | Generating its own color profiles, limiting the ability for consistent color interchange throughout the process |
| • | Producing inconsistent results |
Because color science is so complex, it is impossible to eliminate differences in color space, luminants and colorants, and gamuts. However, implementing color management in the operating system instead of at the application level overcomes many of these problems. Color management technologies in Windows help users consistently reproduce color across scanners, cameras, displays, printers, and applications.
Developers can use the Windows ICM 2.0 API to perform the following functions:
| • | Map colors between devices that have different color gamuts (for example, printers and displays) |
| • | Transform colors from one color space to another (for example, RGB to CMYK) |
| • | Provide accurate on-screen or print previews that allow users to make color corrections |
ICM 2.0 API in the Microsoft Platform SDK
http://msdn2.microsoft.com/en-us/library/ms536514.aspx
To support multiple platforms that may be used throughout the color publishing process, Microsoft is ensuring that applications that support ICM 2.0 will be compatible with other platforms. This compatibility is possible because Microsoft has licensed the industry-standard Hendelberg color management module and supports ICC profiles.
Windows vs. Macintosh color management
For more information, see "sRGB Color Management Case Studies" at http://www.microsoft.com/whdc/device/display/color/default.mspx
APIs for ICC-based support
About 80% support nearly identical functionality, 20% support operating system-specific issues
Microsoft Windows | Apple Macintosh |
ICM 2.0 | Apple ColorSync3 |
Industry standards
Microsoft Windows | Apple Macintosh |
Leading effort to develop IEC standards for quality tolerances | Principally proprietary |
SRGB support and workflows
Default color space for PhotoShop, Windows, PDF, JavaSoft, HTML, SMIL, CSS, PNG, EXIF (most digital cameras), many manufacturers color devices, including professional-quality displays from Sony and Barco
Microsoft Windows | Apple Macintosh |
Native support for industry-standard sRGB workflows | Proprietary sRGB support; all workflows require ICC profiles |
Workflow model
Microsoft Windows | Apple Macintosh |
Designed to support work across multiple applications, work groups, locations, and devices, based on per-device profiles rather than user intervention | Application-centric view: a single artist working with a single application and using a single capture device, a single display, and a single printer |
Visual display calibration
Microsoft Windows | Apple Macintosh |
Third-party support | Built-in and third-party support |
Hardware support
Microsoft Windows | Apple Macintosh |
Widest mass-market device support, based on sRGB compatibility, with testing program established | Based on vendor-supplied ICC profiles, per device |
Support for Adobe PhotoShop and Quark Xpress solutions
Microsoft Windows | Apple Macintosh |
Yes | Yes |
Ease of use
Microsoft Windows | Apple Macintosh |
Simple user interfaces | Complex interface and workflows, relying on multiple separate ICC profiles |
Quality
Depends on the actual profiles provided by device manufacturers. See "sRGB Color Management Case Studies" for reports on suitabilitly of sRGB in professional workflows.
Microsoft Developer Support for Color-Capable Hardware
To help hardware manufacturers deliver new color-capable, Windows-compatible devices to meet growing demand from consumers, Microsoft provides a set of color quality test kits and guidelines. These tools apply for Windows XP, Windows 2000, Windows Me, and Windows 98.
Windows Color Quality Test Kits
Microsoft provides reference files, tools, and instructions for quantitatively measuring the ability of color-capable devices to render sRGB color within certain tolerances of the CIE 1994 DeltaE standard, using the ICM profile supplied with Windows. Windows Color Quality Test Kit for Device OEMs also includes images that manufacturers can use to visually evaluate the color quality of devices.
| • | Kits are currently available for color capable printers, CRT monitors, and transmissive LCD monitors. |
| • | Kits are planned for reflective LCDs, projectors, scanners, and digital cameras. |
Color Quality Test Kits
for printers, CRT monitors, and transmissive LCD monitors:
http://www.microsoft.com/whdc/device/display/color/default.mspx
Windows Logo Program for Hardware.
To ensure that users benefit from Windows color management capabilities when using devices designed to work with Windows, a set of color-management requirements is specified in Microsoft Windows Logo Program System and Device Requirements:
| • | Color-capable devices such as desktop CRT monitors, LCDs on mobile systems, color plasma and other flat-panel devices, and printers are required to install one or more ICC profiles. Any sRGB-compliant device can use the Windows default profile for sRGB. |
| • | Scanners and digital still cameras are required to either install ICC profiles or output sRGB. |
| • | A monitor color-calibrations utility is recommended for generating, editing, and installing ICC profiles. |
Testing is conducted by the Windows Hardware Quality Labs as part of "Designed for Windows" logo testing.
Guidelines for developers
Software vendors |
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Device manufacturers |
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Industry Standards and Activity
CIE technical committee TC8-02 (standards for computing and reporting color differences for images)
http://www.colour.org/tc8-02/
CIE—Commission Internationale de L Eclairage—is an organization for setting standards for color measurement.
IEC Colour Management and Measurement international standards, including IEC 61966-2-1 sRGB Standard
http://www.iec.ch
International Color Consortium (ICC)
http://www.color.org/
The ICC was established in 1993 to create and promote standardization of an open, vendor-neutral, cross-platform color management system architecture and components.
sRGB-related Standards Development
http://w3.hike.te.chiba-u.ac.jp/IEC/100/PT61966/
W3C sRGB Web Site
http://www.w3.org/Graphics/Color/sRGB.html
Resources from Microsoft
Color management information and test kits
http://www.microsoft.com/whdc/device/display/color/default.mspx
WHQL testing for color-capable devices
http://www.microsoft.com/whdc/whql/default.mspx
Windows DDK for device support
http://www.microsoft.com/whdc/devtools/ddk/default.mspx
ICM 2.0 SDK in the Microsoft Platform SDK
http://msdn2.microsoft.com/en-us/library/ms536514.aspx
Feedback or information requests for developers
wincolor@microsoft.com