Monitor Calibration FAQ

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This reserved article originally appeared in CHROMiX ColorNews Issue 1 on Feb 15, 2001.

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by Steve Upton



Contents

Monitor Calibration and Profiling: What's the Difference?

To calibrate is to change the behavior of a monitor (or printer or scanner) to return it to a standard. Periodic calibration will maintain the monitor so that the way it produces color will stay consistent over time.

To Profile is to analyze the monitor to see how it produces its color. With a profile you can tell other applications (like Photoshop, for instance) how to convert color settings so the image looks right on screen.

In practice, most monitor calibration and profiling software performs both of these tasks at once and you may not notice when it moves from one task to another.

I've heard I should calibrate my monitor. Why?

Monitors vary their color output over time as they age and with normal use. Calibration keeps them operating in a stable way and keeps the profile valid.

What is a monitor profile?

A monitor profile is a conversion table that describes how a monitor produces color. It's used by your system and applications to convert colors for display - for when you want that scanned photo to look good on screen. It's also used to convert screen images for use elsewhere - for example, when you've edited an image on screen, like what you see, and want to reproduce the colors on your printer.


How do I calibrate and profile my monitor?

There are a couple of different methods to calibrate and profile your monitor:

  1. Software only. Apple's ColorSync Default Calibrator and Adobe Gamut control panels can both be used to profile and calibrate your monitor "by eye". The software walks you through several steps to set your monitor's gamma and white points, and allows you to select your monitor from a predefined list.
  2. Software and Hardware. Using a colorimeter or spectrophotometer (instruments which measure color output) in conjunction with software will also calibrate and profile the monitor. The hardware is "stuck" right to the surface of the screen and reads multiple color patches.


Is using hardware better? Why use it instead of software alone?

When only software is used, you are left to guess at the phosphor colors the monitor displays. With a hardware instrument the red, green and blue phosphor colors, as well as the white points, are all accurately measured and this builds a much more accurate profile. It also takes into consideration the aging of your monitor.

How often should my monitor be recalibrated or reprofiled?

As you can imagine, this depends on the stability of your monitor and how particular you are about its accuracy. We typically suggest a minimum of once every two weeks. In demanding environments you may want to recalibrate once a week or even every day.


My monitor has color controls. How do they apply?

Higher-quality monitors tend to have controls that allow the adjustment of each red, green, and blue gun, as well as other settings. You should use these in conjunction with your profiling hardware to calibrate your monitor first. Then let the software fine-tune the calibration using your system's graphics card, and profile the monitor. By setting the monitor first you can take advantage of the analog controls in the monitor, rather than the potentially quality-limiting controls in the graphics card, to set the calibration.


I've seen some monitors that have integrated controls and extra cables connecting them to the computer. What difference does this make?

A "smart" monitor like Apple's ColorSync monitor is tied to the computer with an integrated communication cable in addition to the regular monitor cable. This extra computer control helps by automating the calibration process, as well as monitoring the performance of the monitor and keeping it in calibration. Until recently, these monitors were the typical choice for accurate monitor color. But with the advent of quality lower-priced monitors and inexpensive colorimeters, smart monitors are no longer a requirement except for the most demanding environments.


I've heard you can't see all colors on a monitor. Is this true?

It's true. There are also colors your monitor can display that cannot print. It is commonly thought that CMYK printing processes have a smaller gamut than the monitor but, in truth, they overlap each other. Monitors are typically deficient in cyans and often will not display saturated yellows. At the same time, the saturated reds, blues, and greens your monitor can display are out of gamut for most printers and can't be printed. These limitations are classic problems of color management and are the result of the physics of monitors and printing.

I can choose 5000 or 6500 Kelvin as my white point. Which is best?

White point calibration is a point of some discussion. In theory, calibration of your monitor to 5000 Kelvin would achieve a match with a light booth containing 5000 K lights. In practice, however, due to instrument inaccuracies or the differences in human perception between monitor-produced white and paper-reflected light, the calibration may not match. 6500 Kelvin is becoming a popular choice for monitor white points and has just been accepted in a new ISO viewing standard. We suggest 6500 for monitor calibration.

Many monitors ship from the manufacturer at a 9300 Kelvin white point. Manufacturers prefer this blue version of white as it is bright, but the blue guns are fired at a high level and this can drastically affect the life of the monitor. Calibrating your monitor to 6500 or 5000 Kelvin will reduce the wear and tear on your monitor and bring it into more standard viewing conditions.

How about gamma? Should I use 1.8 or 2.2? What is the difference anyway?

Gamma on a monitor is similar to dot gain on press. It describes the mid tones of your images. Monitors can be calibrated to a gamma of 1.8, 2.2 or sometimes everything in between. 1.8 gamma has traditionally been the setting for Macs as it is similar to dot gain on paper. 2.2 is the typical gamma setting for PC monitors and televisions. This gamma difference is the main reason images appear different between Macs and PC's on the web. If your work is headed to the web, 2.2 is probably the best choice, if headed to print 1.8 or 2.2 are both good choices. Experimentation is key.


How bright should the monitor be?

If your profiling tools give readings for brightness, you should shoot for brightness between 85-95 cd/m2 (on a CRT monitor). Any brighter and you run the risk of burning your monitor out too soon. Any lower and you reduce the dynamic range of your monitor too much.


What is the life span of a monitor?

Naturally this depends on many factors, the most important of which is hours of use. In a typical full-time business environment a monitor will have a useful life of 2 to 3 years.


How can I tell when my monitor is at the end of it's useful life?

If you find your monitor is too dim even at full contrast, if there are color casts across the surface of the screen, or focus problems, then it may be time to upgrade to a fresh screen. Time to move it along to accounting.

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