Monitor Calibration
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Monitor Calibration

One of the most important aspects of color management is monitor calibration. If the color isn't right on the monitor, coming up with accurate digital output is almost impossible.

By Stan Sholik

WYSIWYG. (What You See Is What You Get) is one of the primary objectives when working with digital images. The idea is to make sure that the output generated on a digital printer matches what's being displayed on a computer monitor. That involves color management, which, in effect, is color communication between the various input devices, the computer and the various output devices.

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  • Although the entire process is commonly called "calibration" it is actually a two-part procedure: adjusting the monitor, which is also called "calibration", and creating a monitor profile for the specific monitor being used. When the two steps are done correctly, the chances of coming up with accurate output increase significantly.

    Every monitor displays color differently. There are differences between various models when they are new, and these differences can increase as the equipment ages. When uncalibrated, even new monitors don't display color accurately. The human eye (in conjunction with the brain) does a wonderful job of interpreting the brightest areas of the screen to look like neutral white and the darkest parts totally black. The reality is, nearly every monitor when shipped has an overall blue-ish cast because of the initial factory settings.

    To understand why requires a little color theory. Scientists describe colors on a color measurement scale that uses degrees Kelvin (K) as a unit of measurement. Colors are described as being of a certain "color temperature" along this scale.

    The white of a new monitor is generally around 9300K, because this is the default factory setting. A 9300K white is considered very blue. The color temperature of output is determined by the color temperature of the light illuminating it. For print output, viewing booths illuminate the press sheets with 6500K or 5000K light. Transparencies are viewed on 5000K color-corrected light boxes. 6500K is much less blue than 9300K, and 5000K looks downright yellow compared to 9300K! This is just one of the reasons that output will not match the monitor image on an uncalibrated monitor.

    Another reason is called "gamma". This is a term used to describe the way in which brightness transitions from white to black. The lower the gamma of a device, the brighter the mid-value of gray will appear when reproduced on the device. Macintosh systems have standardized on a gamma of 1.8 while Windows has standardized on 2.2, which explains why images appear lighter on a Mac system. But the gamma that the monitor is actually reproducing may or may not be that of the system due to aging of the monitor as well as the characteristics of the video card to which it is attached. Thus the gamma of both the monitor and the video card must be correctly adjusted during calibration.

    With all of the variances between monitors and their tendency to drift from any set value over time, the only way to ensure that images will be consistently displayed is to periodically calibrate them. The problem is compounded in larger imaging labs where the same image may be adjusted by different technicians at different times on different monitors. Unless all of the monitors are calibrated to the same standard, each technician may adjust the image to display "accurately" on the monitor in use, degrading the color and perhaps making it impossible to output properly.

    The steps in calibrating a monitor include adjusting the brightness and contrast controls on the monitor itself to set or perceived values, setting a white point (color temperature), adjusting or selecting a gamma, and defining the red, green and blue phosphors settings. These adjustments are then saved as an ICC profile that now understands the characteristics of the monitor. Macintosh computers store this information as an ICC System Profile while Windows 98, Me, 2000 and Xp store it as an ICM System Profile. Windows NT does not support system-wide color profiles, but will save the information for use with ICC-compliant applications and video cards.

    Other than buying a "self-calibrating" monitor from Barco, the quickest way to calibrate a monitor is to use Adobe Gamma, which is automatically installed in your computer during Photoshop installation. On the Windows platform it is found by clicking Start/Settings/Control Panel and on the Macintosh in Apple/Control Panel. Double-clicking on Adobe Gamma launches the application.

    Adobe Gamma is a perceptual method of color adjustment, meaning that users make adjustments to contrast, brightness, gamma and color phosphors according to what they see. Using the Wizard interface is the most informative the first time through. The first screen instructs the user to set the contrast gain on the monitor to its maximum setting, and then adjust the monitor brightness until a gray square is just slightly different in value from its black surrounding.

    The next screen asks the user to select the phosphor set of the monitor. Film or video professionals will choose PAL, SECAM or NTSC standards from the drop-down menu, but Trinitron is the safest selection for imaging applications, unless the monitor supplier has specific values available that can be input into the Custom boxes.

    Gamma is set in the next screen by moving sliders under red, green and blue squares to set the existing gamma of the monitor. Then the desired gamma for the system in use is set by choosing Macintosh default, Windows default or Custom from the drop-down menu.

    The next screen sets the color temperature of the display. It can be measured perceptually by clicking the Measure button and selecting the most neutral-looking gray patch from a choice of three, a difficult procedure for most users. For imaging labs, it is better to select 5000K or the slightly cooler 5500K setting from the drop-down menu. The 9500K selection is best for Web developers since this will be the way most consumers will view their work on monitors unadjusted from the factory setting.

    On the next screen the user can choose to have the monitor display images at a different white point than set. This is useful to check how an image will display under other monitor conditions.

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    On the final screen, name and save the profile. The file will be automatically stored in the appropriate folder in your computer.

    Those working in imaging labs know that there are many variations between operators in the way that they see color, even the same operator will see color differently at different times. So this or any perceptual method of color adjustment such as Apple's Monitor control will lead inconsistent results.

    For more accurate, repeatable results, monitor calibration can be done with software in combination with a hardware colorimeter or spectrophotometer.

    Colorimeters are three-color instruments for measuring transmitted or reflected light. They are the devices most often used to calibrate and profile the monitor, though they can be used for generating printer profiles. However, their limitation to reading three colors limits their accuracy for this use.

    Spectrophotometers are more sophisticated instruments for reading the reflectance or transmittance of light at specified increments throughout the visible spectrum. These devices are most commonly used to create output profiles from printers but are also used for highly accurate monitor calibration and profiling.

    In some cases, software is available that works with a number of different hardware units; in others, the software and hardware are sold as a package and can only be used together. With both types, the user loads the calibration software, connects the hardware unit, and follows a procedure determined by the software to calibrate and profile the monitor.

    Color Encore for Monitors from Southwest Software (www.swsoft.com) works in conjunction with several hardware measurement devices such as the X-Rite DTP92 colorimeter to perform monitor calibration and profiling on Macintosh or Windows machines.

    ColorVision's Monitor Spyder is one of the most popular monitor calibration and profiling devices that requires its own proprietary software to function. The Monitor Spyder is bundled with either PhotoCal software or the more complex OptiCal software that allows multiple monitors to be matched to a common standard. The colorimeter is available for USB interface only and is available for Mac and Windows platforms.

    Eye-One Monitor is part of GretagMacbeth's family of Eye-One profiling products (www.i1color.com). This monitor calibration and profiling package is available separately or as a module in the other products. Included is the Eye-One spectrophotometer that can be used with both CRT and LCD monitors.

    Other companies sell complete profiling packages that not only do monitor calibration and profiling, but handle scanner and output device profiling also.

    Monaco Systems (www.monacosys.com) provides an extensive line of profiling products for Windows and Mac platforms that include monitor calibration and profiling. All are compatible with Monaco's MonacoSENSOR colorimeter. The higher end packages will also support a wide range of third-party colorimeters and spectrophotometers.

    Several profiling packages that include monitor calibration and profiling are offered by Praxisoft (www.praxisoft.com), including WiziWYG Plus for Mac and Windows platforms and WiziWYG Deluxe for Macintosh computers. Both products include the WiziWYG Calibrator Monitor colorimeter or can be used with the SpectroStar Spectrocam spectrophotometer.

    ProveIt! from ITEC (www.color.com) can be used as a perceptual monitor profiling program or in conjunction with ColorBlind's ProveIt! colorimeter to profile both CRT and LCD monitors on Mac and Windows systems. ColorBlind Matchbox is also available as software only, with ColorBlind's colorimeter or with the SpectroStar Spectrocam spectrophotometer. ITEC's high-end profiling package, ColorBlind Professional is available with ProveIt! colorimeter, SpectroStar Spectrocam spectrophotometer or X-Rite's DTP-41 spectrophotometer.

    Once the monitor profile is generated by one of these programs, named and saved in the computer, one last step will ensure that the operating system (OS) will access this information.

    In the ColorSync Control Panel of Macintosh OS, set the profile in the Display pop-up menu. In Windows 98 and 2000, set the profile in Control Panel/Display/Settings/Advanced/Color Management. From this screen, the profile can be selected by clicking the Add button. When you select the profile and click Set As Default, it becomes available to any program that supports ICC profiles.

    Monitor calibration and profiling is only the first step in ensuring WYSIWYG results, but they're important steps. They must be handled correctly for color management to have any chance of being effective in the production process.

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