Arts Technology Arts TechnologyThe steps towards practical color management include the calibration of the devices in the production pipeline, the creation of industry-standard International Color Consortium (ICC) Profiles to characterize the color response of each device, and the use of a Color Management System (CMS) to apply profiles when moving color information, such as images, from device to device.
Programs can then use the CMS to match colors which are within the gamut of both devices, map colors which are out of gamut to within the gamut of later devices, convert color information from one system to another, and preview colors by using a monitor or printer to simulate the color-look of the final output device.
As was noted in the previous article, the Apple Macintosh OS has led the industry in its support for color management. Since that article was published, Apple has improved their CMS with the release of ColorSync 2.5. Standards-based color management for Microsoft Windows and NT still await the release later this year of ICM 2.0.
While much of this article addresses the specifics of the Macintosh OS and its ColorSync CMS system, the same principles apply to other systems such as Windows95, NT, and UNIX workstations.
The apparently simple manual adjustment of brightness and contrast settings is an important part of monitor calibration, which is seldom done properly by most users. The brightness control, also called "black level," is usually depicted by a sun icon -- a full circle sometimes surrounded by rays or lines. The contrast control, called "picture" by video technicians, is usually marked by a moon icon -- a split circle, half light and half dark.
Be sure to allow any monitor 30 minutes to warm up before attempting any calibration. First, turn the contrast control to its lowest setting. Next, adjust the brightness control to the threshold point where the black area of the picture emits no light but any higher adjustment would result in dark gray rather than black. This sets the black level to true black. Finally, the contrast control should be turned up to set the preferred intensity for white.
While this can be done to taste, it's important to avoid an overly intense image, as this may result in flicker or a loss of focus and contrast. The midrange response, or gamma, and the overall color temperature, or white point, of the monitor can be adjusted as well, with some additional hardware and software.
In the past, a number of third-party gamma adjustment control panels have been available for the Macintosh. With ColorSync 2.5 installed, these should be avoided. The Monitors and Sound control panel now includes a "calibrate" button which will take you through the various steps and provide on-screen displays for adjusting and visually checking the results.
In addition, hardware colorimeters can be used with the included software to calibrate monitors in a more exacting manner, and some monitors include built-in hardware calibration features. For best results, monitor calibration should take place at least once a month, and as often as once a week.
In a professional setting, where color fidelity is critical, additional steps are usually taken to enhance the monitor viewing environment. The room lighting elements should be chosen to deliver a standard 5000 degree color temperature as per the D50 illumination standard for critical viewing. In addition, a hood around the monitor may be used to eliminate glare. Colorful or busy designs on the computer desktop should be avoided, and a light gray background which approximates an 18 percent density is strongly recommended. Finally, the room itself can be painted light gray (a 36 percent density or Munsell N8), and colorful shirts should be avoided to minimize reflected color on the monitor.
Generic profiles can be used to improve color matching, but even two calibrated devices of the same brand will still exhibit visually significant color differences. To overcome these differences, custom profiles specific to each physical device must be created. This can be quite time-consuming in a complex production environment, as each physical input, output and display device requires the creation of a custom profile.
To create a scanner profile, first scan the appropriate IT8 target. It is important to note the various settings used in the scanning software, as these must be held constant in future scans when using this profile.
An application program, such as ColorSynergy from Candela, can then be used to create an ICC Profile. Select the data file for the corresponding IT8 target and open the scanned image file. After manually clicking on some of the registration marks in the scanned image being displayed, the program can automatically compare the exact color values for the scan with those on the corresponding data file, and use the differences to generate an ICC Profile.
Later, when scans are made to use in applications such as Photoshop or QuarkXPress, the corresponding ICC Profile can be selected, and the image will be corrected for the known color response of that scanner.
A spectrophotometer is a device that breaks the continuous rainbow-like spectrum of light into bands, and then measures the overall intensity of each band. For the purposes of color management, 32 spectral bands are typically measured and used. Some spectrophotometers, such as the Colortron II from X-Rite, are hand-held devices that can be used to create printer profiles, and to measure and match colors in the real world, such as the red on a Campbell's Soup label. Other devices, such as the DTP41 from X-Rite, are automatic scanning devices optimized for fast ICC Profile creation.
The Colortron II spectrophotometer, shown with a 285-color patch sample output from a color printer being profiled.
Measuring the color patches with a hand-held device can be very time-consuming. For example, measuring the 285 color patches used by Print Open ICC with the Colortron II can take one or two hours, whereas an automatic device can make the needed measurements in just a few minutes.
The PrintOpen ICC uses this display to mark each color patch on the screen as it is measured with a photspectrograph.
Once the software has all of the color patch data, it can compare the measured colors with the known data it used to produce the printout, and then generate an ICC Profile.
For example, a set of three free plug-ins for Adobe Photoshop are available to allow users to import, export and process images using ICC Profiles. TIFF and JPEG files can be created with embedded ICC Profiles, so that the source profile for the image is always available when the image file is used with other ColorSync applications. QuarkXPress 3.2 users wanting to take advantage of ColorSync have had to use third-party commercial plug-ins, but QuarkXPress 4.0 integrates ColorSync support into the package.
For those creating graphics for the Web, using a well-calibrated monitor along with ICC Profiles for both the scanner and monitor will help provide consistent results. There is little you can do about users who have not set up their monitor properly. There are, however, free plug-ins available from Pantone that allow a viewer's browser to use ColorSync when displaying images with embedded ICC Profiles on a profiled monitor.
For artists creating color output directly on digital printers such as the 3M Rainbow or Epson 3000, using ColorSync with a printer profile and a calibrated, profiled monitor can help detect and eliminate nasty color shift and other gamut-related problems. If you specify the target printer, the monitor can display a simulation of the printer's colorspace.
For those creating color images that will eventually go to press, ICC Profiles can be used to simulate the look of the press on the user's monitor. This is called a "soft proof." In addition, by specifying profiles for both the target press and a locally available color printer, you can use inexpensive paper output to simulate an eventual press run.
All computer users can benefit from calibrating their monitors. In addition, those working on projects with serious color fidelity concerns should integrate color management into their workflow. They should also create their own custom profiles whenever possible, rather than use generic profiles.![[ C ]](../icons/CSmSum98.gif){kind=icon}
In addition, the Arts Technology area of the Innovation Center is being configured for robust color management support. A number of high-resolution devices are being calibrated and profiled for ICC and ColorSync compatibility, including 21-inch Radius PressView monitors for soft proofing, a multiformat Leaf 45 film scanner, an 8000 line Lasergraphics Mark III recorder for 35mm and 4 by 5 photographic film, and several art quality color printers.
Departments in the arts with their own facilities may want to contact the ACF Arts Technology Group for help in creating profiles for their scanners, monitors and printers. In addition, profiles for ATG output devices will be made available so that work for output on these devices can be prepared at home or on departmental systems.
Because of our limited resources, Arts Technology Group support is generally restricted to academic programs in the arts. For example, we cannot provide production support for ongoing University or administrative publications.
Posted May 18,1998
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