4.7.3 BASIC CALIBRATION
See
Section
4.6.3
for help with picture calibration. Most of the basic steps for pixel-based
displays apply except for CRT projectors. They may have more control over color balance, which
generally involves the ability to calibrate and store color balance per projector source memory.
Setting contrast or peak white level is more difficult with a CRT projector as the blue tube will
normally be close to beam current-limiting at full IRE100 output over the whole screen. This can
result in a color balance shift to red at very high output levels and also prevent the standard test
disc methods of setting contrast from working 100% correctly. Some contrast level setting
procedures used on test DVDs rely on the projector’s power supply voltage sagging under the
load imposed. However, the majority of CRT projectors originate as over-specifed commercial
units, where the power supply is unlikely to lower its output under high load conditions. Start
with the projector’s contrast setting the same as you have previously used*, then make
adjustments to obtain correct peak white levels on a variety of source material.
Correct
might be
defined as
realistic looking
or
comfortable to view
.
* Some projectors have a very high manufacturer’s default contrast setting (ss high as 80%). Depending on projector model, tube condition and
screen gain a contrast setting of 50-60% is more likely to produce realistic levels. As a side benefit, useable tube life will be significantly extended.
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