ADAPTIVE HISTOGRAM EQUALIZATION
The AHE process can be understood in different ways. In
one perspective the histogram of grey levels (GL’s) in a window
around each pixel is generated first. The cumulative distribution
of GL’s, that is the cumulative sum over the histogram, is used
to map the input pixel GL’s to output GL’s. If a pixel has a GL
lower than all others in the surrounding window the output is
maximally black; if it has the median value in its window the
output is 50% grey.
This section proceeds with a concise mathematical description
of AHE which can be readily generalized, and then
considers the two main types of modification. The relationship
between the equations and different (conceptual) perspectives
on AHE, such as GL comparison, might not be immediately
clear, but generali