Image Enhancement
ENHANCEMENT BY POINT PROCESSING
If the pixel values f(x, y) occupy only a limited range (m, M) in the available range (n, N), contrast may be enhanced in the displayed image g(x, y) by the linear transformation.
The same transformation may also be used to stretch a small range of gray levels of interest to the available display range.
This is useful in displaying computed tomography images, which have a large dynamic range of (-1024, 1024).
A small density range of interest may be extracted from the full range for improved display; the method is then known as density slicing or gray ever windowing.
Nonlinear transformations may also be used for selective gray level stretching and compression.
linear gray scale transformation