A Fast Algorithm For Space Variant Contrast Stretching

The operation of convolution (for the purpose of edge enhancement) can be decomposed into two terms, one of which varies quite slowly over the image being filtered. By the use of two dimensional interpolation, this spatial redundancy may be exploited in order to achieve a fast two dimensional convolution procedure for a particular class of operators. Viewed in this sense, conventional (linear) edge enhancement may be interpreted as a dynamic shifting of the "local mean". A space variant contrast stretch <1,2,3> may then be seen as a non-linear procedure in which both the local mean and the local standard deviation of an image are dynamically shifted. The same fast algorittm may then be applied to the nonlinear space variant case.