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/* find position of maximum, subpixel estimation
*
* Copyright: 2008, Nottingham Trent University
* Author: Tom Vajzovic
* Written on: 2008-02-07
*
* 25/1/11
* - gtk-doc
*/
/*
This file is part of VIPS.
VIPS is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA
*/
/*
These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif /*HAVE_CONFIG_H */
#include <glib/gi18n-lib.h>
#include <stdlib.h>
#include <vips/vips.h>
#include <vips/vips7compat.h>
#define MOST_OF( A, B ) ( (A) > 0.9 * (B) )
#define LITTLE_OF( A, B ) ( (B) < 0.1 * (B) )
/**
* im_maxpos_subpel:
* @in: input image
* @x: output position of maximum
* @y: output position of maximum
*
* This function implements:
*
* "Extension of Phase Correlation to Subpixel Registration"
* by H. Foroosh, from IEEE trans. Im. Proc. 11(3), 2002.
*
* If the best three matches in the correlation are aranged:
*
* 02 or 01
* 1 2
*
* then we return a subpixel match using the ratio of correlations in the
* vertical and horizontal dimension.
*
* ( xs[0], ys[0] ) is the best integer alignment
* ( xs[ use_x ], ys[ use_x ] ) is equal in y and (+/-)1 off in x
* ( xs[ use_y ], ys[ use_y ] ) is equal in x and (+/-)1 off in y
*
* Alternatively if the best four matches in the correlation are aranged in
* a square:
*
* 01 or 03 or 02 or 03
* 32 12 31 21
*
* then we return a subpixel match weighting with the sum the two on each
* side over the sum of all four, but only if all four of them are very
* close to the best, and the fifth is nowhere near.
*
* This alternative method is not described by Foroosh, but is often the
* case where the match is close to n-and-a-half pixels in both dimensions.
*
* See also: im_maxpos(), im_min(), im_stats().
*
* Returns: 0 on success, -1 on error
*/
int im_maxpos_subpel( IMAGE *in, double *x, double *y ){
#define FUNCTION_NAME "im_maxpos_subpel"
int xs[5];
int ys[5];
double vals[5];
int xa, ya, xb, yb;
double vxa, vya, vxb, vyb;
if( im_maxpos_vec( in, xs, ys, vals, 5 ))
return -1;
#define WRAP_TEST_RETURN() \
\
/* wrap around if we have alignment -1 < d <= 0 */ \
/* (change it to: size - 1 <= d < size ) */ \
\
if( ! xa && in-> Xsize - 1 == xb ) \
xa= in-> Xsize; \
\
else if( ! xb && in-> Xsize - 1 == xa ) \
xb= in-> Xsize; \
\
if( ! ya && in-> Ysize - 1 == yb ) \
ya= in-> Ysize; \
\
else if( ! yb && in-> Ysize - 1 == ya ) \
yb= in-> Ysize; \
\
if( 1 == abs( xb - xa ) && 1 == abs( yb - ya )){ \
*x= ((double)xa) + ((double)( xb - xa )) * ( vxb / ( vxa + vxb )); \
*y= ((double)ya) + ((double)( yb - ya )) * ( vyb / ( vya + vyb )); \
return 0; \
}
#define TEST3( A, B ) \
if( xs[0] == xs[A] && ys[0] == ys[B] ){ \
xa= xs[0]; \
ya= ys[0]; \
xb= xs[B]; \
yb= ys[A]; \
vxa= vals[0]; \
vya= vals[0]; \
vxb= vals[B]; \
vyb= vals[A]; \
WRAP_TEST_RETURN() \
}
TEST3( 1, 2 )
TEST3( 2, 1 )
if( MOST_OF( vals[1], vals[0] ) && MOST_OF( vals[2], vals[0] )
&& MOST_OF( vals[3], vals[0] ) && LITTLE_OF( vals[4], vals[0] )){
#define TEST4( A, B, C, D, E, F, G, H ) \
if( xs[A] == xs[B] && xs[C] == xs[D] && ys[E] == ys[F] && ys[G] == ys[H] ){ \
xa= xs[A]; \
xb= xs[C]; \
ya= ys[E]; \
yb= ys[G]; \
vxa= vals[A] + vals[B]; \
vxb= vals[C] + vals[D]; \
vya= vals[E] + vals[F]; \
vyb= vals[G] + vals[H]; \
WRAP_TEST_RETURN() \
}
TEST4( 0, 3, 1, 2, 0, 1, 2, 3 )
TEST4( 0, 1, 2, 3, 0, 3, 1, 2 )
TEST4( 0, 3, 1, 2, 0, 2, 1, 3 )
TEST4( 0, 2, 1, 3, 0, 3, 1, 2 )
}
im_warn( FUNCTION_NAME, "registration performed to nearest pixel only: correlation does not have the expected distribution for sub-pixel registration" );
*x= (double) xs[0];
*y= (double) ys[0];
return 0;
}
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