Help for DIFNEAR

PURPOSE:
difnear compares a pixel in the first image with a window of
pixels in the second image.  The minimum of the dif's over
the window is output.  So if two images are slightly misregistered
this program will do a better job of eliminating a lot of "noise"
in the dif image.  It is also possible that "signal" will be wiped
out by a nearby pixel that accidentally has the same value as the
signal.  

The dif value is the closest value.  So the dif of 5 with the values
4 and 7 is 1.  The dif of 5 with 3 and 6 is -1

difnear has an option for refining the window to half step values
and options for taking absolute value of the diff or adding 128.
EXECUTION:

Example

difnear (A,B) C      will dif A and B starting naming the result 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.


TIMING: 

About the same speed as convolution filter.  

 ORIGINAL PROGRAMMER:    A. Zobrist          27 Jun 2002
 COGNIZANT PROGRAMMER:   A. Zobrist          27 Jun 2002
 
 REVISION HISTORY
  2002-06-27 AZ  Initial version
  2008-01-02 WLB Switched to USES_ANSI_C AND LIB_CARTO; misc cleanup  
  2015-11-24 WLB Migrated to MIPL
  2022-07-14 B. Crocco afids to opensource
  

PARAMETERS: