Monitor calibration - equipment instructions

How to ensure what you see on the computer's monitor is accurate
Words by John Tinsley

Calibrating the monitor is the first, and perhaps the most important step in setting up a digital workstation. The monitor image is the only view you have of a digital file, and the quality of all image retouching depends on how accurately the monitor displays it.

There is a wide range of tools available. There are expensive hardware and software packages which measure colour directly off the screen. Some monitors, like the Radius PressView and Apple ColorSync, include calibration software that can be used to set up the monitor in the first place, and then automatically update it as the phosphors age.

There is a fundamental difference in the way that monitor calibration is handled in the Mac and Windows platforms. On the Macintosh, a monitor calibrator creates an ICC profile that is used at system level to correct the monitor image at system start up. Whatever application software is used, the monitor will always display a calibrated image, and this is one of the major advantages of the Apple system. In Windows, calibration changes will generally only appear when ICC compatible applications are run, and not necessarily at system start up. Because of the way some PC graphics cards work, monitor gamma settings are not always software adjustable, especially when the computer shares memory between system and graphics functions. This means a system-wide calibration can't always be used on the Windows PC.

Adobe Gamma Control Panel
The way out of this is to use the Adobe Gamma calibrator, and this program comes as part of Adobe Photoshop from version 5.0 onwards. It has the advantage that it is available to both Windows PC and Mac users, and is automatically installed in the Control Panels folder or directory by default both on the Mac and in Windows 98.

Select the stored monitor profile that appears to match your monitor closest from the list in the load menu.

Now adjust the monitor's contrast control to maximum, and set the brightness control so that you can just discern a difference between the two centre squares. Tape over the monitor controls so they can't be moved accidentally. You have now set the dark point of your monitor.

Now enter the phosphor setting best suited to your particular monitor if you know it. The menu gives a choice of a set of pre-defined phosphors, Trinitron for example, or you can contact the monitor manufacturer and obtain the x-y r, g and b numeric values. These can then be entered in the custom phosphors dialogue box.

The next menu allows you to set the mid-tone values. These should always be set on a colour by colour basis, so make sure the view single gamma only box is unticked. Red, green and blue squares are provided, and a slider under each square should be adjusted until the centre square disappears. With this done, the monitor gamma should be entered in the panel, either Macintosh default (1.8) or Windows default (2.2) depending on the platform.

Next, make sure your white point matches that of your monitor. This is when equal values of red, green and blue at full intensity produce white on your monitor screen. This is a pre-set value for all monitors, and is usually a choice of standard CIE colour temperatures. These are:

5000K - D50 or page white

6500K - D65, the accepted Windows default

7500K - D75

9300K - D93, the accepted Mac default

Generally, setting the Mac or Windows defaults will be OK, however the Adobe gamma control panel will allow the white point to be measured approximately. Selecting measure will display three grey squares on screen. Clicking on the left square will add blue to the centre square, whilst the right will add yellow. When the centre square is as neutral as possible, store the measured white point.

With the dark, mid-tone and white points set, your monitor is now calibrated. Store these settings as an ICC or ICM profile that will be called up each time the computer is started up (Macintosh) or each time an ICC compliant application is loaded (Windows).

When complete you see a screen that lets you view the monitor before and after calibration has taken place. Click on the before and the after circles to see the difference. If it looks right click on finish if not click on back and re adjust.

Apple's system level ColorSync monitor calibrator for the Mac is available for free download from Apple's web site. This will generate a monitor profile operating at true system level, giving full colour management facilities to ColorSync savvy applications.

The calibration procedure is very similar to the Adobe gamma control panel, in that brightness and contrast controls are first set to establish the dark point of the monitor.

The mid-tone gamma is then set by moving sliders on red, green and blue patches exactly as in the Adobe program.

Then, target gamma is set. Choose 1.8 if your images are likely to remain on a Macintosh, or 2.2 if they will be viewed on a Windows PC.

Then set the target white point to 9300 in the next menu.

Finally save your new custom monitor profile.