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       im_match_linear_search, im_match_linear - resample to make a match


       #include <vips/vips.h>

       im_match_linear( IMAGE *ref, IMAGE *sec, IMAGE *out,
          int xr1, int yr1, int xs1, int ys1,
          int xr2, int yr2, int xs2, int ys2 )

       im_match_linear_search( IMAGE *ref, IMAGE *sec, IMAGE *out,
          int xr1, int yr1, int xs1, int ys1,
          int xr2, int yr2, int xs2, int ys2,
          int hwindowsize, int hsearchsize )


       im_match_linear_search()  attempts  to  transform  sec to make it match
       ref. The transformation is linear, that is,  it  only  involves  scale,
       rotate and translate.

       im_match_linear_search()  requires  a  pair  of  tie  points to fix the
       parameters of its transformation. You should pick points as  far  apart
       as  possible to increase accuracy. im_match_linear_search() will search
       the area in the image around each tie point for a  good  fit,  so  your
       selection  of points need not be exact. WARNING! This searching process
       will fail for rotations of more than about 10 degrees or for scales  of
       more  than  about  10  percent.  The best you can hope for is < 1 pixel
       error, since the command does not attempt sub-pixel correlation.

       hwindowsize and hsearchsize set the size of the area to be searched: we
       recommend values of 5 and 14.

       The  output image is positioned and clipped so that you can immediately
       subtract it from orig to obtain pixel difference images.

       im_match_linear() works exactly as im_match_linear_search(),  but  does
       not  attempt  to  correlate  to correct your tie points. It can thus be
       used for any angle and any scale, but you must be far more  careful  in
       your selection.




       J.Ph.Laurent - 12/12/92
       J.Cupitt - 22/02/93

                                  13 May 1991                  MATCH_LINEAR(3)