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6 Enhancement
in conjunction with a logarithmic transformation to reduce illumination
effects; this approach is briefly discussed at the end of Section 6.3.3.
6.2.3 Gray Scale Transformation
We next consider gray scale transformations that are the same at every
point of the picture (or a region), rather than varying from point to point.
Such a transformation can be expressed as a mapping from the given gray
scale ζ into a transformed gray scale z', i.e.,
z' = t(z)
We shall assume that in both the old and new gray scales, the allowable range
of gray levels is the same, i.e., ζ
γ
^ ζ < z
K
and z
r
< z' < z
K
. We can now dis-
cuss how to desig