Basic Information on imheq

Task: imheq
Purpose: Apply histogram equalization to an image
Categories: map manipulation

IMHEQ -- applies histogram equalization to an image.  This
technique generates a cumulative histogram of an image.  The
ordinate for this histogram (number of pixels) is then also
discretized into the prescribed number of bins.  Each image
pixel is then replaced by the value of the cumulative 
histogram bin that it contributed to.  This essentially means
that in terms of a non-cumulative histogram of the image,
equal numbers of pixels have fallen into each intensity bin
so that the bins are not of equal intensity width.  This
technique enables you to see best the intensity range that
has the most pixels.

Image pixels which are flagged by the image mask will not 
contribute to the histograms.  However, they will be equalized 
in the output image (although their mask will be unchanged).


Key: in
The input image. No default.

Key: out
The output image. No default.

Key: nbins
The number of bins for the image histogram.   Default is 128.

Key: range
The intensity minimum and maximum to bin in the histogram.
Pixels outside this range are set to the nearest limit.
Default is to use the full image plane range.  Over-rides
OPTIONS=GLOBAL below.

Key: options
"global" means use the global image minimum and maximum as the
   histogram limits for all image planes.  By default, each
   image plane is equalized with the intensity minimum and 
   maximum from that plane.

Key: device
PGPLOT device to show plots of the histograms & discretized
cumulative histogram. Will plot after each plane, so really 
of use only for single plane images

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