Applications and operating systems that know about color will finally make effective color management available to the mainstream user
Michael Sugihara
Color is more available and less expensive than ever. But the neophyte color user faces a confusing and frustrating situation. After struggling to get a presentation to look just right on the monitor, you are given obscure and unhelpful choices in a printer setup dialog box--"more vivid color," "matches the screen," or "automatic color." After making adjustments to get a desktop ink-jet printer to produce the proper colors, you send the job to the network's high-speed color laser printer for duplication and to a thermal-transfer printer for transparencies. The most expensive surprise of all comes when you send the job to the local print shop for mass duplicat
ion on a four-color press. No two of these outputs look quite the same.
If color is to be an effective tool, you must be able to create and enforce consistent, predictable color along the processing chain: scanners, software, monitors, desktop printers, external PostScript output devices, prepress service bureaus, and printing presses. Unfortunately, professional use of color, particularly in the printing and graphics industries, has always been seen as an art, not a science, requiring human intervention throughout the process.
Technology must intervene, and people are still waiting for a good solution. But help is on the way. Many color-matching and color management schemes are coming to market or are already here, including Eastman Kodak's Precision Color Management System, Hewlett-Packard's ColorSmart, Apple's ColorSync, Pantone's ColorDrive, Tektronix's TekColor, EFI's EfiColor, and Agfa-Gevaert's FotoFlow.
Why So Difficult?
The dilemma of color management is th
at different devices just can't create the same range of colors. Some colors can be easily viewed on a monitor but can't be output accurately on certain printers. Conversely, printing processes can easily produce colors that monitors can't display. Finally, different printing processes have their own limitations.
Color is created on a computer screen in a different fashion than it is on paper. The computer screen emits light directly, but most color that we see in the real world is reflected light. A standard CRT monitor creates color by causing red, green, and blue phosphors (thus, an RGB monitor) to glow. These phosphors on a black mask can simulate a wide range of colors. This system is called additive color. (Color monitors are treated in greater depth in "On-Screen Color".)
Printed material is created by applying inks or toner to white paper. The pigments in the ink absorb light selectively so that only parts of the spectrum are reflected back to the viewer's eye (hence the term subtractive
color). The basic printing ink colors are cyan, magenta, and yellow, and a fourth ink, black, is usually added to create purer, deeper shadows and a wider range of shades. This four-color ink process is called CMYK.
Do You See What I See?
The everyday office environment also complicates color management. Ambient light directly affects what you see when viewing a color monitor or hard copy. Sunlight has more blue and green in it than red, and incandescent light has much more red. Fluorescent lamps tend to spike in the green range, and their noncontinuous-spectrum light can further distort colors.
There are also variations among devices, pigments, and media. The phosphors used in CRT displays vary in color and intensity from brand to brand and lot to lot. They change over time. The pigments in inks and toners also vary, and the nature of the pigment can alter its appearance. For example, a fluorescent pigment appears brighter because it absorbs light from outside the visibl
e spectrum and then emits it at a different, visible wavelength. Some types of paper soak up ink-jet ink differently than other types. A paper's whiteness can also vary. Surface characteristics of paper--gloss, texture, and color--change the way people perceive colors.
This perception is perhaps the biggest variable. In general, the eye is more sensitive to yellows and oranges than it is to blues. This sensitivity varies from person to person and usually becomes more exaggerated with age.
Color Spaces
How do you describe color in a meaningful, objective way? Most color systems define color in terms of a 3-D color space. The most common systems are RGB for monitors and CMYK for printers. Unfortunately, both these color spaces are device-dependent, because they describe the levels of the signals sent to the device, not the color those signals produce. Send 100 percent red and 100 percent green signals to two different monitors side by side, and you'll see different shades of
yellow.
The CIE (Commission Internationale de l'Eclairage) was formed early in this century to develop standards for the specification of light and illumination. From a series of experiments run in the late 1920s, the CIE averaged subjective responses to color patches illuminated by a standard light source and created a series of mathematical transformations. From these, they derived three theoretical primary sources--named X, Y, and Z--that could be combined to produce all colors visible to the human eye. In rough terms, X represents the amount of redness in a color, Y the amount of greenness and lightness (bright-to-dark), and Z the amount of blueness. This system was adopted as the CIE XYZ model, and it's the basis for most other color space models.
It's difficult to illustrate the CIE XYZ model because of its three dimensions. Thus, a 2-D transformation, called the CIE x,y model, was created by separating the achromatic portions (i.e., blacks, whites, and grays) from the chromatic (i.e., th
ose containing hues). A color's position in this space is given by calculating coordinates where the x value is the ratio of the redness value divided by the total reflectance: x = X/(X+Y+Z). The y value is the ratio of the greenness value divided by the total reflectance: y = Y/(X+Y+Z). The resulting color space, or chromaticity diagram, is shown in the figure "
CIE Color Space
."
Translating device-dependent color spaces to an objective color space and back again is the fundamental challenge for color management systems. Some use lookup tables while others use transforms. If the lookup table is too small or the transform method too simplistic, however, rounding errors can lead to color shifts or image degradation. Ultimately, the quality of the output is the only real indicator of a color management system's success.
Color Management Basics
The ideal color management system should enable color control throughout the desktop environment, independent of any
individual device's capabilities and limitations. To see how systems accomplish this, consider two fundamental functions: calibration and characterization.
Calibration puts a device into a known state. Variables such as ambient lighting, media characteristics, and pigments must be taken into account, and the viewing environment must be stable. If ambient lighting changes--as sunlight coming through a window--the perception of colors on a monitor will change. For professional work, calibration is mandatory.
Characterization describes the relationship of a device's calibrated state to an RCS (reference color space). The ideal RCS allows both the precise specification of a color and intuitive color selection. Each color management vendor has its own proprietary RCS and characterization methodology. All supply profiles for popular input, display, and output devices. However, devices may require periodic recharacterization to maintain accuracy. For example, monitor phosphors react to temperature and
change color with age.
Where Color Management Belongs
Until Apple introduced ColorSync as a part of its System 7.x operating system in 1992, color management was left to specific applications. For example, Adobe Systems' PageMaker 5.0 uses the Kodak Precision CMS, and QuarkXPress 3.2 is bundled with an EfiColor XTension. These high-end systems have produced impressive results, but they are computationally intensive and mutually incompatible (see "Lost in Color Space").
Another approach is to put color selection parameters into the printer driver, as HP has done with its ColorSmart technology. Not a true color management system, ColorSmart tries to anticipate what you expect in color output, with the emphasis on predictability, vibrancy of color, clarity of text, and subjectively appealing colors. Color accuracy per se takes a back seat. This approach is helpful for the casual user, but it works against the overall goal of a WYSIWYG color environment.
Putting color m
anagement into the operating system, as opposed to into applications, allows any application to take advantage of color management and will theoretically result in predictable and consistent color. In practice, however, some trade-offs between color management accuracy and system performance still exist.
Standards Please!
Recognizing the problems of cross-platform color, the ICC (International Color Consortium, although originally named the ColorSync Profile Consortium) was formed in March 1994 to establish a common device profile format. The founding companies included Adobe, Agfa, Apple, Kodak, Microsoft, Silicon Graphics, Sun Microsystems, and Taligent.
The ICC published its first standard--version 3 of the ICC Profile Format--in June 1994. Apple plans to integrate the new ICC format into its QuickDraw GX, and SunSoft has committed to using the format in its Solaris operating system. Perhaps most important, Microsoft's promised Windows 95 will also use the ICC format.
The fact that the three most prominent operating environments will support the same device color profiles is important, but it doesn't guarantee that they will work the same. In fact, the ICC Profile Format is designed to be extensible to allow basic color management and to meet high-end prepress production needs. There are also provisions for "private" codes in the format, which some people fear may make certain profiles less flexible and thus complicate cross-platform compatibility.
Windows 95 and ICM
Windows 95 will be the first Microsoft operating environment to include color management, which will be called ICM (Independent Color Matching). This uses a default color-matching module licensed from Kodak, along with device profiles for many common monitors, scanners, and printers. ICM is also expected to be included in a future release of Windows NT.
As of press time, Microsoft hadn't released a Windows 95 beta that included ICM, so the exact implementation and use
r interface are still unknown. But Microsoft and others have discussed many of ICM's technical and architectural elements. According to Myron Kassaraba, Kodak's director of licensing for color management products, Windows 95 will ship with 83-size (8 bits describing each of the three color components) device profiles. This is the smallest profile that will produce good results in the desktop environment. ICM's 12-bit transform engine for color matching can also handle more robust profiles (163 and 323) in professional applications, though at the expense of overall performance. Because ICM will accept the ICC Profile Format, third-party peripheral makers need develop only a single profile for Macintosh, Windows 95, and Unix environments.
ICM's design will reportedly allow you to "plug in" third-party color-matching engines to replace the default Kodak technology. Expect Agfa, EFI, and Pantone to provide such engines during the next 12 months.
Apple's ColorSync 2.0
Although
ColorSync has been around since 1992, only a few applications suppliers have used its functionality. ColorSync 1.0 was criticized as not being flexible enough for both casual and professional color users. Also, version 1.0 lacked direct CMYK support, using only the CIE XYZ model for device independence and RGB for QuickDraw compatibility.
ColorSync 2.0 has yet to ship, but it will establish the ICC Profile Format as a practical matter. With this product, Apple will take the industry a long way toward making cross-platform color management a reality. ColorSync 2.0 adds the CMYK color model, so it will support most color printers. It will also support earlier Macintosh technology, including the original QuickDraw and the new QuickDraw GX, and can use version 1.0 profiles and APIs. In ColorSync 2.0, the interaction between applications and color management has been simplified. Third-party color management modules can be used for some devices and the default module for others.
But ColorSync and ICM
don't address all your color needs. Both offer basic color management through a device-independent color space model, and device profiles for common displays, scanners, and printers. But neither supplies the tools needed to fully integrate color use into everyday computing. Companies such as EFI, Kodak, Pantone, and Trumatch provide value-added software that will enhance the functionality of the built-in systems. These include tools to match desktop color output to four-color press output and color calibration for individual scanners and monitors.
Pantone's POCE and ColorDrive
In 1963, Pantone (Carlstadt, NJ), a leader in color-reproduction technology, introduced to the printing industry its first color system, PMS (Pantone Matching System). Now it offers many software tools for color management, notably POCE (Pantone Open Color Environment) and ColorDrive.
Announced in October 1993, POCE is the result of a collaboration between Pantone and Light Source Computer Images (La
rkspur, CA) to develop a color management system applicable to photographic color and printed spot color. (Spot color is a part of an image that is printed with a single-colored ink or toner, not a combination of colors). POCE has since been overshadowed by Microsoft's selection of Kodak technology and by Apple's continuing efforts with ColorSync. As a result, Pantone is concentrating its efforts on its traditional strong point, industry-standard spot colors, according to Andy Hatkoff, Pantone's director of business development.
It can be difficult to take a color created in one application and use it in another. Most solutions are based on standardized palettes created from a fixed number of colors. Unfortunately, these systems don't easily support custom colors. Pantone's ColorDrive, announced last September, is designed to standardize palettes, letting different applications use the same colors and enabling proofing devices (e.g., desktop color printers) to produce output that closely reflects what
will be produced via offset or gravure presses. ColorDrive encompasses Pantone's color systems and lets you import and export custom colors between applications. Printer output is calibrated for printers that contain Pantone-licensed palettes and for any printer with ColorSync 1.0-compatible profiles. ColorDrive should be available for the Mac (68K or native Power Mac) this month; a Windows 95 version is scheduled for the second quarter.
Trumatch SwatchPrinter
Trumatch (New York City) created the first process-color matching system specifically designed for digital output. Based on a clever use of the HSB (hue, saturation, brightness) color space, it, too, requires human intervention at the final step of the professional printing cycle. According to Trumatch president Steve Abramson, this is unavoidable, because no current computerized color management tools can yet replace the human eye. The differences between the color capabilities of monitors, color printers, and the four-col
or press, he says, are still large enough that no amount of manipulating the color space data will result in a "perfect" match.
Color printers--whether ink-jet, thermal-transfer, laser, or dye-sublimation--cannot faithfully reproduce all the colors produced by the inks of a four-color printing press. Trumatch's SwatchPrinter software lets you print a 27-page reference showing the 2000+color Trumatch palette, along with each color's CMYK percentages, on a color PostScript printer. This output can be compared with a Trumatch color swatch fanbook showing the same colors printed on a four-color press, which will pinpoint any differences and simplify color selections for final printing.
Closing in on Consistent Color
Effective color management has come much closer to reality in the past year than many people thought possible. Virtually all major color participants have embraced the new device profile standard, and this year will see color management widely incorporated in opera
ting systems. For the first time, you will begin to see cross-platform compatibility through standardized device profiles and third-party software.
Full color management will still require considerable intervention by trained human eyes and considerable expense. The color professional will find his or her job a little easier because of these improvements. For the rest of us, however, predictable desktop color may, at long last, become a reality this year.
illustration_link
The CIE x,y model is a 2-D representation of the full 3-D CIE XYZ color space model. The lines on this figure represent the limits (gamut) of color monitors and of web-offset printing.
Michael Sugihara is vice president of MWA Consulting, Inc., of Palo Alto, California, an industry-analyst organization that focuses on printing and imaging issues. You can contact
him on the Internet at
mwac@apple.link.apple.com
or on BIX c/o "editors."
Consistent Color
