Name

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CORREL_OPTIMIZE

Purpose

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Find the optimal (x,y) pixel offset of image_B relative to image_A
  EXPLANATION"
Optimal offset is computed by means of maximizing the correlation
function of the two images.

Calling Sequence

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

Inputs

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image_A, image_B = the two images of interest.

Optional Input Keywords

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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

Outputs

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

Calls

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function correl_images( image_A, image_B )
pro corrmat_analyze

Procedure

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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.

Modification History

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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