Color Management and Windows: An Introduction
Updated: December 4, 2001
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Introduction to Color Management
Color Is Pervasive Across Media, Yet Difficult to Reproduce Consistently
Over the years, magazines, newspapers, television, computers and, now, the Internet have all made the transition from black and white to color.
Now that all of these media use color, they all provide professional designers with the challenge of finding a way to get consistent color from page to screen to printer and beyond. Consistent color across various displays and types of output is critical to success. For example, in the publishing industry, consistent color throughout the commercial publishing process will save both time and money. Designers want to ensure that their clients' printed material will produce the same results when the job is passed to the service bureau, trade shop, and printer and that it will also look great when it's made available on the Internet.
The same is true for business professionals developing color presentations, or consumers wanting to buy products from an Internet site. All of these users expect "true," or what-you-see-is-what-you-get (WYSIWYG), computer color across all input and output peripherals, and across various publishing and productivity applications.
With color, however, WYSIWYG results across scanners, monitors, applications, and printers are often difficult, or impossible, to achieve for two reasons:
If you have a computer peripheral capable of capturing, displaying, printing, or in some other way dealing with color at a user visible level, you are already aware of some of the problems inherent with dealing with color in the digital world. If you have ever tried to buy a "Forest Green" shirt on the Internet, and then wondered about the actual color of the shirt you received in the mail, you have experienced the problems first hand.
Color management does not solve all of these problems magically; it simply gives you and the user more control. Basically, each color peripheral can differ on one or more of the following color characteristics:
These differences are unavoidable in most cases, because of the limitations of the devices or media in question. However, these differences can be tested for and recorded in an International Color Consortium (ICC) profile using one of many software and hardware products currently available on the market. These ICC profiles are then used to communicate through the rest of the Integrated Color Management (ICM) system to ensure that colors are represented accurately to users, regardless of the device they use.
Because color science is so complex, it is impossible to completely eliminate the above differences. However, there is a way to improve the situation - a color management system. CMS performs three main functions:
Why Color Management is Required
Color Management at the Operating System-Level Brings Advantages Over Application-Specific Color
In the publishing process, images and graphics are captured by scanners and digital cameras as well as from CDs, and they are brought together in editing and composition packages. From here, design professionals use a variety of proofing systems to simulate the final printed output and, ultimately, generate film for plate generation for final delivery to commercial printing presses. Designers also take these graphics to the Internet. Business and home users are likely to deliver their final graphics to a color printer, to the Internet, or to an intranet in corporate environments.
The publishing process is summarized in the following figure:
Figure 1. The publishing process
Being able to consistently reproduce color across scanners, monitors, printers, and applications sounds like a simple goal, but without a color management system in the operating system, it's difficult to achieve.
Without a standard CMS, each application writes to a different proprietary color management system with little or no interaction with the operating system. Each application generates its own color profiles, limiting the ability for consistent color interchange throughout the publishing process, which includes scanning, editing and composition, proofing, and distribution. The applications may produce different results.
Figure 2. Application-specific color management
In addition, each application must supply profiles for all kinds of devices, as well as profile generation tools for all types of devices, a disadvantage to both the application developer and to the user.
As a result of each application generating its own profiles for every conceivable device, and in the absence of consistent interchange between devices, acceptable color on the output is achieved largely through trial and error.
Image Color Management Features
ICM Background and HistoryMicrosoft Corporation first implemented CMS in the Microsoft Windows 95 operating system as Image Color Management (ICM) 1.0, an API to which third-party applications can write. This version of ICM was designed to address the needs of applications that work with RGB, to work seamlessly for the end user, and to enable simple support from application developers.
ICM 1.0 supports profiles that conform to the International Color Consortium (ICC) profile specification. The ICC profile specification is a cross-platform industry standard that accurately and consistently characterizes devices including scanners, monitors, and printers. The ICC started in 1993 as an organization to promote color standards with desktop applications.
ICM profiles must be installed for all of the color devices on the user's system, and applications that need to portray colors accurately must support the ICM 1.0 API.
The ICM 1.0 technology 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 slightly different RGB values displayed on a monitor or sent to printers.
For additional information about profiles andother color management technologies, see "For More Information" at the end of this article.
ICM 2.0 Features
After listening to customers and application vendors, Microsoft enhanced the capability of ICM to provide increased functionality and performance and to bring it to the Windows operating systems. Microsoft also wanted support for more color spaces (beyond RGB to CMYK, to device-independent color spaces such as CIELAB, a theoretical color space defined by the Commission Internationale de L'Eclairage, or CIE), as well as support for additional colors for processes such as HiFi Color.
Working with multiple industry leaders in the color field, Microsoft has designed ICM 2.0. The new APIs are a complete superset of the ICM 1.0 APIs and add a new range of capabilities:
ICM 2.0 supports the LinoColor color management module (CMM) as the default CMM. The CMM transforms color information across various devices. Linotype-Hell AG is one of the leading vendors of color technology in the publishing and prepress world. This technology is now expected to become available to all applications that support the ICM 2.0 API.
ICM 2.0 supports up to eight input and output color channels for enhanced printing processes such as HiFi Color.
This new version of ICM is integrated into Windows 98 and Windows 2000.
ICM Supports Industry Standards, Ensuring Cross-Platform Compatibility
By licensing the industry-standard LinoColor CMM and continuing support for ICC profiles, Microsoft is helping to ensure that applications that support ICM 2.0 will be compatible with other platforms, a fact that is important because multiple platforms may be used throughout the color publishing process.
Like ICM 1.0, ICM 2.0 supports the ICC profiles, allowing the same device profiles to be used across platforms and ensuring better color management throughout the publishing process.
ICM Provides Ease-of-Use for Applications
For productivity and entry-level publishing applications, ICM 2.0 can be configured to be completely transparent to the end user.
For professional publishing applications, full manual control is available, in each case ensuring color consistency across devices and platforms. In addition, for professional publishers, ICM provides an easy-to-use selection method for choosing alternative profiles.
ICM Has a Modular, Extensible Architecture
Applications will have the ability to support two levels of API - one that deals only in RGB, and one that works in multiple color spaces. As developers take advantage of these enhanced capabilities, users will be able to manage device profiles and select an alternate CMM for their color transformations.
The architecture is summarized in the following figure:
Figure 3. ICM 2.0 technology overview
ICM Supports Standard RGB (sRGB)
ICM provides a standard way to manage color between any input device (e.g., scanner) and output device (e.g., monitor), including the ability to embed ICC profiles directly into the image or to pass the ICC profile directly to the application. The application, along with ICM and the rendering intent, generates a transform that ensures accurate color representation between the input and output device.
Embedding the ICC profile into each image is an excellent way to ensure that the color profile information is being passed along throughout the publishing process. However, the additional overhead it adds to the image may be unacceptable for transmission over the Internet. Also, several image formats currently do not support embedded ICC profiles, which makes it very difficult to represent the color image accurately.
Hewlett-Packard Co. and Microsoft have created a new color space, standard RGB (sRGB), that is meant to complement current color management strategies by enabling another method of handling color in the operating system and the Internet. It will provide good quality color representation and backward compatibility, with minimum transmission and system overhead. Based on a calibrated colorimetric RGB color space, which is well-suited to monitors, television, scanners, digital cameras and printing systems, sRGB can be supported with minimum cost to software and hardware vendors.
In addition, both companies have worked with the World Wide Web Consortium (W3C) to ensure that sRGB is available to all vendors. sRGB has been the standard color space since HTML 3.2 and Cascading Style Sheets (CSS) 1.0, and it is freely available to any software or hardware vendor.
Microsoft also plans to make sRGB the default color space in Windows 98 and Windows 2000 operating systems for all color images that do not have an embedded ICC profile, or for images that are not specifically tagged with other color information. This will help ensure that colors are represented in a way that looks best on the widest range of devices.
A summary of when sRGB is expected to be used is outlined in Figure 4. The "source" referred to in the figure could be a scanner, and the "destination" could be a monitor.
Figure 4. sRGB is used as the default color space in the color mapping process
"Designed for Microsoft Windows" Requirements for Color Management
To ensure that your device benefits from the color management capabilities of ICM 1.0 and 2.0, a set of requirements is specified for imaging in the Windows Logo Program for Hardware.
The Windows family of operating systems support using color profiles that comply with the ICC Profile Format specification. The ICM APIs and functionality are described in the Microsoft Platform SDK and the Windows DDK.
Color-capable devices such as desktop CRT monitors, LCDs on mobile systems, color plasma and other flat-panel devices, and printers are all required to install one or more ICC profiles for ICC color management. A monitor color-calibrations utility is recommended for generating, editing, and installing ICC profiles. Scanners and digital still cameras are required to either install ICC profiles or output sRGB. The sRGB profile is available in Windows 98/Me and Windows 2000/Windows XP.
For More Information