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Monitor Calibration and Web Color Consistency by Joel Mattox

Abstract

This paper describes the role of monitor calibration in the pursuit of color consistency on the Internet, and provides background on the color production methods of the major desktop and portable display devices. It provides descriptions of various means of measurement and adjustment, and background on relevant industry standards such as ICC profiles.

Contents

Catalog publishers know the importance of consistent color in their imagery: an image instills emotion and sets expectations in the audience's mind. However, an image's actual color appearance is affected by the way color is produced by the print media. Thus, the pre-press industry faces the challenge of creating on PCs and printing with inks on volume production presses. The resource- intensive solutions for this industry reflect both the importance of consistent color as well as the technical challenge of creating, editing, proofing and finally printing color images on devices that produce color by widely different means with controllable results. 

For most of us, who aren't producing content for million-copy runs on offset presses, the technical challenges of color consistency are somewhat less daunting but still complex. For those of us creating content for the web to be shown on our visitors' displays, the problem boils down to this: how can our teams collaborate effectively to create sites with images that will display with consistent color on our visitors' monitors?

Background: Impact of system differences

Differences between the designs and configurations of monitors and of display controllers will cause the same picture file to appear differently from one screen to the next. What's more, even the same monitor will show colors differently when connected to different video cards. If you've used a PC to look at an image created on a Macintosh or vice versa, you've seen this effect in washed out colors or pictures that seem impossibly dark. For an illustration of how computer display systems produce color, visit: www.trueinternetcolor.com/EffectDemo/system.htm

As a result of system differences, the image files you work with for your site will appear differently to your colleagues when they view them. This can lead to a productivity-draining series of image edits, as each colleague sequentially reacts to the image as displayed on his or her unique system and tweaks it to 'look right.' What's worse, the finished image will appear differently to visitors viewing them on their specific systems than they did to your team, and the differences will vary for each visitor. Visit: www.trueinternetcolor.com/EffectDemo/webcolorshifts.htm for a demonstration of this effect which you can do with two computers at your own site. 

Even the web safe palette (colors which aren't dithered when viewed cross- platform in 256 color mode) isn't immune from the effect of system differences: for a demonstration using only web safe colors, visit. www.trueinternetcolor.com/EffectDemo/websafeshifts.htm 

Though today's web environment poses a challenge to color consistency, new tools and creative use of existing tools provide the basis for authoring web sites with great, consistent color.
Available Tools

Driven initially by the broad challenges faced by the pre-press industry, color management tools and standards have been developed, many of which can be adapted to the needs of the web developer. Some of the most relevant are:

Standard descriptions of color capabilities
The International Color Consortium, http://www.color.org/ , sets forth a standard way to describe the ability of a device to produces color in a data file, called an ICC profile. Typical monitor ICC profiles are quite small, about 2-4 Kbytes.

Monitor Characterization Solutions
Unlike printers that have integrated controllers, display systems have separate controllers and monitors. Thus color characteristics must be measured, or characterized, in the field after purchase and user configuration. Software utilities and hardware devices, such as Pantone's Pantone Personal Color Calibrator (P2C2) and X-Rite's Monitor Optimizer, are available to measure an installed display system's color behavior as configured and create an accurate ICC monitor profile for that specific installation from the results. 

Monitor Calibration Solutions
Some of the software and hardware utilities can use the characterization measurement data to change, or calibrate, display behavior to a known or desired state. Authoring organizations can use these tools to set all their monitors to display colors consistently, improving productivity during production and editing cycles. Calibration utilities regenerate a new ICC monitor profile when/if calibration settings are changed.

OS infrastructure
Microsoft's Image Color Management (ICM), built into Windows versions since Windows 95, and Apple's ColorSync use ICC profiles and provide ways for applications to correct images, depending on the difference between the ICC profile for the local system and a profile for the device the image was created on.

Authoring Software
Image authoring and web editing tools, such as Adobe's Photoshop and GoLive, that work with ICC profiles and operating system color management tools provide a platform for collaborating as a team on web content in a color-consistent manner.

Server Color Correction
E-Color, Inc. has recently announced True Internet Color Server, which uses ICC authoring profiles and web-based calibration to customize image colors specifically for each visitor's system. For more information on server color correction, visit http://www.ecolor.com/ or http://www.trueinternetcolor.com/

Calibration Solutions in Context
Each of the tools above plays a crucial role in a color-consistency solution. Note that a common underlying thread is reliance on an accurate ICC monitor profile. Let's now focus on monitor characterization and calibration. We'll use the process followed by the Windows version of Colorific V99 as an illustration, however the processes used by other calibrators will follow the same general path.

Monitor measurement [characterization]
This is the foundation for all display color correction: measuring the monitor and controller as a system. To measure a monitor, the software provides a set of carefully constructed images on the screen. Interactions between parts of each image, as viewed by the person doing the calibration, provide the data used to determine the system display characteristics. For an example of a calibration image, visit www.trueinternetcolor.com/EffectDemo/calibrate.htm

With the measurement complete, characterization software proceeds to write an ICC monitor profile and store it where needed by the operating system, as well as maintain the characterization information for later use in calibration.

Monitor adjustment [calibration]
Modern display controllers have an update feature that can be used to change the display system behavior by changing look-up-table contents by software. Calibration software guides the owner to select among pre-set calibration options, (or to create their own settings) compares the setting to the characterization information, and calculates the changes needed to the look-up-table to effect the change. The software then updates the look-up table values to calibrate the monitor, writes a new ICC profile reflecting the calibration, and adds startup routines so that subsequent sessions will automatically bring the display system from its default power-on state to the calibrated state.

Pulling it all together
Consistency begins at home, to paraphrase an old saying: the web authoring workflow is not immune to the color shifts caused by system differences. It is critical to have all systems characterized: as we've seen accurate ICC monitor profiles are essential for any operating system or application color consistency machinery to work Further, although it's not always possible, getting your team to agree on a color setting and calibrating all your displays to that setting will improve your productivity.

An image file with an accurate ICC profile of the display it was authored on describes the image's colors in enough detail that software can adjust to prevent color shifts as it's shown on other systems. Embedding an author profile into each image and using image and web editing applications that manage profiles effectively helps authors collaborate (even if they are not calibrated to the same setting, the authoring tools can use the embedded author profile and the local monitor profile to adjust for differences) and prepares the image for publication.

When publishing for color correction, the profiles created by the calibration and/or characterization processes are crucial: server based color correction uses the image file and the authoring profile as a basis to adjust images for visitors' systems. Client based color adjustment approaches also rely on the authoring profiles for an image to describe its colors.

Conclusion
System differences and the color shifts they cause can be managed, if measured and corrected for. Display systems, being configured in the field, need to be characterized after installation. For some workflows, the display systems should then be calibrated to consistent color settings. An accurate ICC monitor profile, created by the characterization/ and calibration processes, is a crucial part of all web color consistency efforts. The monitor profile from the author's system, together with the image file itself, then describes the image's colors sufficiently for either client or server approaches to web color consistency. 

As we've seen, monitor characterization and calibration solutions are an essential infrastructure for consistent web color.
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Disclaimer and Copyright
True Internet Color and Colorific are registered trademarks of E-Color, Inc. 739 Bryant St., San Francisco, CA 94107 415/957-9940 http://www.ecolor.com/ (c) 1999, E-Color, Inc. All rights reserved. All product names may be trademarks or registered trademarks and are the property of their respective owners.

This article was published on Wednesday 15 November, 2006.
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