Gamma is an implicit or explicit transfer function that maps input intensity to output
intensity, usually in a nonlinear way. The most common example is a CRT monitor,
where the brightness onscreen is less than expected based on the input voltage. If the
input voltage ranges between 0 (black) and 1 (white), one would expect a voltage of
0.5 to generate a brightness value of about 50 percent gray on the screen, but in fact
only 18 percent gray is generated. This is simply the nature of a CRT’s electron gun
response to input voltage.
The CRT applies an implicit power function in which the input signal is raised to the
power of 2.5 (V
). Gamma is usually defined by the value of the exponent in the power
function—in this case, 2.5.