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Contrast enhancement is a very important issue in processing and
analysing image, is a fundamental step in analyzation and segmentation image.
These are mainly two categories: (1) indirect method of contrast enhancement
and (2) direct method of contrast enhancement.
a) About indirect method
There are many indirect techniques, which were proposed in references.
They only modifies the histogram, without using any contrast measure.
In recent years, many researchers have applied fuzzy set theory to
develope new techniques to enhance the contrast of the image.
Fuzzy approach algorithms often lead to the requirement of designing a
gray-scale transformation S-shape function (The function is continuous
monotonous increase, decreasing the input gray level when the input is below
the threshold, and increasing the value gray level input when the input is above
the threshold). However, the selection of functions in the fuzzy rule inference to
produce the gray-scale transformation S-shape function is not easy. With the
following simple fuzzy rule
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