.TH MATCH_LINEAR 3 "13 May 1991"
.SH NAME
im_match_linear_search, im_match_linear \- resample to make a match
.SH SYNOPSIS

#include <vips/vips.h>

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

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

.SH DESCRIPTION
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.

.SH SEE ALSO
im_lrmosaic().
.SH AUTHORS
J.Ph.Laurent \- 12/12/92
.br
J.Cupitt \- 22/02/93