CORREL_OPTIMIZE

       Find the optimal (x,y) pixel offset of image_B relative to image_A

       Optimal offset is computed by means of maximizing the correlation
       function of the two images.

       CORREL_OPTIMIZE, image_A, image_B, xoffset_optimum, yoffset_optimum
               [ XOFF_INIT=, YOFF_INIT=, MAGNIFICATION=, /PRINT, /NUMPIX,
                 /MONITOR, PLATEAU_THRESH=  ]

       image_A, image_B = the two images of interest.

       XOFF_INIT = initial X pixel offset of image_B relative to image_A,
       YOFF_INIT = Y pixel offset, (default offsets are 0 and 0).
       MAGNIFICATION = option to determine offsets up to fractional pixels,
                       (example: MAG=2 means 1/2 pixel accuracy, default=1).
       /NUMPIX: sqrt( sqrt( # pixels )) used as correlation weighting factor.
       /MONITOR causes the progress of computation to be briefly printed.
       /PRINT causes the results of analysis to be printed.
       PLATEAU_THRESH = threshold used for detecting plateaus in
               the cross-correlation matrix near maximum, (default=0.01),
               used only if MAGNIFICATION > 1.    Decrease this value for
               high signal-to-noise data

       xoffset_optimum = optimal X pixel offset of image_B relative to image_A.
       yoffset_optimum = optimal Y pixel offset.

       function  correl_images( image_A, image_B )
       pro  corrmat_analyze

       The combination of function correl_images( image_A, image_B ) and
       corrmat_analyze of the result is used to obtain the (x,y) offset
       yielding maximal correlation. The combination is first executed at
       large REDUCTION factors to speed up computation, then zooming in
       recursively on the optimal (x,y) offset by factors of 2.
       Finally, the MAGNIFICATION option (if specified)
       is executed to determine the (x,y) offset up to fractional pixels.

       Written, July,1991, Frank Varosi, STX @ NASA/GSFC
       Added PLATEAU_THRESH keyword  June 1997,  Wayne Landsman  STX
       Converted to IDL V5.0   W. Landsman   September 1997

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