Help for GTSTAT

PURPOSE:

gtstat applies a window to each pixel location (mirroring at the 
edges, see OPERATION), calculates the mean or standard deviation,
multiplies by a user selected constant, and outputs the value for
the center pixel of the window.  The result is an image.

EXECUTION:

Example

gtstat A B        will calculate the standard deviation of A using 
                  the default 3x3 window and put the result in C.
                               
gtstat A B 'MEAN  will calculate the mean of A using the default
                  3x3 window and put the result in C.
                               
OPERATION:

Because of the window, the program uses a "rolling barrel" of input
lines to avoid rereading a line more than once in the second input.

The image is not really mirrored at the edges, but calculates the
calculated statistic on the intersection of the window with the image.
The difference is an overweighting of the non-reflected pixels in
the calculated statistic, but this is a minor effect.  In a sense, 
mirroring would overweight the reflected pixels, so who is to say
which is better.

TIMING: 

About the same speed as convolution filter.  

 ORIGINAL PROGRAMMER:    A. Zobrist          15 Dec 2003
 COGNIZANT PROGRAMMER:   A. Zobrist          15 Dec 2003
 
 REVISION HISTORY
  2003-12-15 AZ  Initial version
  2003-12-22 AZ  Added mean, kept sigma as default
  2008-01-02 WLB Switched to USES_ANSI_C AND LIB_CARTO; misc cleanup  
  2015-10-23 WLB Migrated to MIPL