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Definition of contrast
If a visual stimulus varies in intensity, either in space or in time, it is possible to define a maximum and minimum intensity. The ratio between these intensities is known as contrast. If the output of a source changes from I1 at t1 to I2 at t2, the contrast is
(
I
1
-
I
2
)
(
I
1
+
I
2
)
This measure of contrast is often termed modulation. It is evident that the maximum value for contrast is 1.0 when I2 = 0. A similar definition can be used when contrast is measured in a complex spatial scene. Sometimes, however, if the image consists of a single edge, the contrast is taken as ΔI/Iavg, where averaging over the entire image occurs.
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