On CRT monitors, the Brightness control adjusts the Black Luminance level of the
monitor. The Contrast control adjusts the White Luminance level.
On some LCD monitors this is also true but it is difficult to determine. LCD monitors
may also have a third control called Backlight that is different than the Brightness or
Contrast control. Some LCD monitors have only a Backlight control that is usually
confusingly labeled with the same icon that is used for the Brightness control (a sun).
Our general experience with LCD monitors that have Brightness and Contrast controls
is that the monitor performs best if those controls are set to their Factory Default
values. You may experiment with the adjustment of these controls but this is not
recommended and it is up to you to determine whether or not you get better results.
When calibrating in
Visual
mode, the user is prompted to turn the Contrast control to
maximum, which means that the monitor will work at its highest White Luminance
value. The user is prompted to adjust the Brightness control based on observation of a
visual target that should result in an appropriate Black Luminance level. While this
may seem unscientific, optimal black luminance is affected by ambient light. Since this
is the case, a visual judgment by the end user that takes into account ambient light
often yields a better result than if a number was to be handed down through the ages
by a color god.
If Black Luminance is too low then dark tones will display as black and there will be a
loss of shadow detail. If Black Luminance is too high then black will appear as a dark
gray instead of a pure black and shadow detail will appear washed out or lacking in
contrast.
The purpose of
Measured
mode is that once appropriate Target Luminance Values
have been determined you can accurately reproduce these levels from one calibration
to the next by measuring the Black and White Luminance of the monitor using the
colorimeter instrument.
So the real question is how to determine Target Luminance Values. That is the title of
this section after all. It may be that your System Administrator or similar source has
already provided you with Luminance Targets. If not then what you want to do is