pro corrmat_analyze, correl_mat, xoffset_optimum, yoffset_optimum, \$ max_corr, edge, plateau, \$ XOFF_INIT = xoff_init, \$ YOFF_INIT = yoff_init, \$ REDUCTION = reducf, MAGNIFICATION = Magf, \$ PRINT = print, PLATEAU_THRESH = plateau_thresh ;+ ; NAME: ; CORRMAT_ANALYZE ; PURPOSE: ; Find the optimal (x,y) offset to maximize correlation of 2 images ; EXPLANATION: ; Analyzes the 2-D cross-correlation function of two images ; and finds the optimal(x,y) pixel offsets. ; Intended for use with function CORREL_IMAGES. ; ; CALLING SEQUENCE: ; corrmat_analyze, correl_mat, xoffset_optimum, yoffset_optimum, ; max_corr, edge, plateau, [XOFF_INIT=, YOFF_INIT=, REDUCTION=, ; MAGNIFICATION=, PLATEAU_THRESH=, /PRINT] ; ; INPUTS: ; correl_mat = the cross-correlation matrix of 2 images. ; (as computed by function CORREL_IMAGES( imA, imB ) ). ; ; NOTE: ; If correl_mat(*,*,1) is the number of pixels for each correlation, ; (the case when /NUMPIX was specified in call to CORREL_IMAGES) ; then sqrt( sqrt( # pixels )) is used as correlation weighting factor. ; ; OPTIONAL INPUT KEYWORDS: ; XOFF_INIT = initial X pixel offset of image_B relative to image_A. ; YOFF_INIT = Y pixel offset, (both as specified to correl_images). ; REDUCTION = reduction factor used in call to CORREL_IMAGES. ; MAGNIFICATION = magnification factor used in call to CORREL_IMAGES, ; this allows determination of offsets up to fractions of a pixel. ; PLATEAU_THRESH = threshold used for detecting plateaus in ; the cross-correlation matrix near maximum, (default=0.01), ; used only if MAGNIFICATION > 1 ; /PRINT causes the result of analysis to be printed. ; ; OUTPUTS: ; xoffset_optimum = optimal X pixel offset of image_B relative to image_A. ; yoffset_optimum = optimal Y pixel offset. ; max_corr = the maximal correlation corresponding to optimal offset. ; edge = 1 if maximum is at edge of correlation domain, otherwise=0. ; plateau = 1 if maximum is in a plateau of correlation function, else=0. ; ; PROCEDURE: ; Find point of maximum cross-correlation and calc. corresponding offsets. ; If MAGNIFICATION > 1: ; the correl_mat is checked for plateau near maximum, and if found, ; the center of plateau is taken as point of maximum cross-correlation. ; ; MODIFICATION HISTORY: ; Written, July-1991, Frank Varosi, STX @ NASA/GSFC ; Use ROUND instead of NINT, June 1995 Wayne Landsman HSTX ; Remove use of non-standard !DEBUG system variable W.L. HSTX ; Converted to IDL V5.0 W. Landsman September 1997 ;- scm = size( correl_mat ) if (scm[0] LT 2) then begin message,"first argument must be at least 2-D matrix",/INFO,/CON return endif Nx = scm[1] Ny = scm[2] x_shift = Nx/2 y_shift = Ny/2 if N_elements( xoff_init ) NE 1 then xoff_init=0 if N_elements( yoff_init ) NE 1 then yoff_init=0 if (scm[0] GE 3) then begin ;weight by # of overlap pixels: Npix_mat = correl_mat[*,*,1] Maxpix = max( Npix_mat ) corr_mat = correl_mat[*,*,0] * sqrt( sqrt( Npix_mat/Maxpix ) ) endif else corr_mat = correl_mat max_corr = max( corr_mat, maxLoc ) xi = (maxLoc MOD Nx) yi = (maxLoc/Nx) if N_elements( Magf ) NE 1 then Magf=1 if N_elements( reducf ) NE 1 then reducf=1 if N_elements( plateau_thresh ) NE 1 then plateau_thresh=0.01 plateau=0 edge=0 if ( reducf GT 1 ) then begin xoffset_optimum = ( xi - x_shift + xoff_init/reducf ) * reducf yoffset_optimum = ( yi - y_shift + yoff_init/reducf ) * reducf xoffset_optimum = round( xoffset_optimum ) yoffset_optimum = round( yoffset_optimum ) format = "(2i5)" endif else if ( Magf GT 1 ) then begin w = where( (max_corr - corr_mat) LE plateau_thresh, Npl ) if (Npl GT 1) then begin wx = [ w MOD Nx ] wy = [ w/Nx ] wxmin = min( wx ) wymin = min( wy ) wxmax = max( wx ) wymax = max( wy ) npix = (wxmax - wxmin)+(wymax - wymin) if (Npl GE npix) AND \$ (xi GE wxmin) AND (xi LE wxmax) AND \$ (yi GE wymin) AND (yi LE wymax) then begin plateau=1 xi = wxmin + (wxmax - wxmin)/2. yi = wymin + (wymax - wymin)/2. max_corr = corr_mat[xi,yi] endif endif xoffset_optimum = xoff_init + float( xi - x_shift )/Magf yoffset_optimum = yoff_init + float( yi - y_shift )/Magf format = "(2f9.3)" endif else begin xoffset_optimum = xi - x_shift + round( xoff_init ) yoffset_optimum = yi - y_shift + round( yoff_init ) format = "(2i5)" endelse if (xi EQ 0) OR (xi EQ Nx-1) OR \$ (yi EQ 0) OR (yi EQ Ny-1) then edge=1 if keyword_set( print ) then begin mincm = min( corr_mat, minLoc ) if (scm[0] GE 3) then begin xm = (minLoc MOD Nx) ym = (minLoc/Nx) Npixmin = Long( Npix_mat[xm,ym] ) * reducf * reducf Npixmax = Long( Npix_mat[xi,yi] ) * reducf * reducf info_min = " ( " + strtrim( Npixmin, 2 ) + " pixels )" info_max = " ( " + strtrim( Npixmax, 2 ) + " pixels )" endif else begin info_min = "" info_max = "" endelse print," min Correlation = ", strtrim( mincm, 2 ), info_min print," MAX Correlation = ", strtrim( max_corr, 2 ), info_max,\$ " at (x,y) offset:", \$ string( [ xoffset_optimum, yoffset_optimum ], FORM=format ) if (plateau) then begin print," plateau of MAX Correlation:" print," (Correl - MAX + " + \$ string( plateau_thresh, FORM="(F5.3)" ) + ") > 0" print,(corr_mat - max(corr_mat) + plateau_thresh) > 0 endif if (edge) then begin print," Maximum is at EDGE of shift range, " + \$ "result is inconclusive" print," try larger shift or new starting offset" endif endif return end