Why Is Gamma Correction Needed - HP b2600 Administration Manual

Why Is Gamma Correction Needed?

The intensity of light generated by a conventional monitor is non-linear with respect to the signal
applied. The intensity output is approximately equal to the applied voltage raised to a power. This power
is referred to as the gamma of the monitor. Stated mathematically,
gamma
intensity = voltage
For example, the gamma value of a properly adjusted monitor is usually between 2.35 and 2.55. Ideally,
to produce an image that is 50% intensity, you would specify color values that are 50% of the maximum
value. However, a monitor with a gamma of 2.4 would generate an intensity that is only 19% of the
2.4
maximum intensity (0.5 = 0.19).
The intensity principle is illustrated in the following test patterns. The pattern on the left has an area
with exactly 50% brightness directly next to an area of horizontal stripes that alternate 100% brightness
with 0% brightness. From a distance, the intensity of each area should be about the same. The middle
pattern is basically the same, but just a little dimmer.
Figure 13: Brightness
Once the brightness and contrast of your monitor are adjusted properly (see below), you can run the
gamma correction tool (also described below) to see its effect on the test patterns above.
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Graphics Administration Guide for HP-UX 10.20