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/*=============================================================================
** Lynkeos
** $Id: corelation.c,v 1.6 2005/01/27 23:13:27 j-etienne Exp $
**-----------------------------------------------------------------------------
**
** Created by Jean-Etienne LAMIAUD on Apr 30, 1998
** Copyright (c) 1998,2003-2005. Jean-Etienne LAMIAUD
**
** This program is free software; you can redistribute it and/or modify
** it under the terms of the GNU 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 General Public License for more details.
**
** You should have received a copy of the GNU General Public License
** along with this program; if not, write to the Free Software
** Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
**
**-----------------------------------------------------------------------------
*/
#include <stdlib.h>
#include <assert.h>
#include "corelation.h"
/*=============================================================================
** correlate_spectrums
**-----------------------------------------------------------------------------
**
** Purpose : correlate on precomputed spectrums
**
**-----------------------------------------------------------------------------
**
** Entry :
**
**
** Output :
**
**=============================================================================
*/
void correlate_spectrums( FFT_DATA s1, FFT_DATA s2, FFT_DATA r )
{
u_short x, y, c;
u_long i;
/* Fourier transform of correlation is the product of s1 by s2 conjugate */
for( i = 0; i < r.nplanes*r.h*(r.w/2+1); i++ )
r.spectrum[i] = s1.spectrum[i] * ~s2.spectrum[i];
fourier_inverse( r, NULL, NULL );
/* Transpose the quadrants, to bring origin at the center */
for( y = 0; y < r.h/2; y++ )
{
for( x = 0; x < r.w/2; x++ )
{
for( c = 0; c < r.nplanes; c++ )
{
REAL r1 = *colorValue(r,x,y,c),
r2 = *colorValue(r,x,y+r.h/2,c);
/* Exchange NW & SE quadrant */
*colorValue(r,x,y,c) = *colorValue(r,x+r.w/2,y+r.h/2,c);
*colorValue(r,x+r.w/2,y+r.h/2,c) = r1;
/* Exchange NE et SW quadrant */
*colorValue(r,x,y+r.h/2,c) = *colorValue(r,x+r.w/2,y,c);
*colorValue(r,x+r.w/2,y,c) = r2;
}
}
}
}
/*=============================================================================
** correlate
**-----------------------------------------------------------------------------
**
** Purpose : Correlation of two images
**
**-----------------------------------------------------------------------------
**
** Entry : Two images in an array of COMPLEX
**
**
** Output : Correlation in an array of COMPLEX (although the i part is null)
**
**=============================================================================
*/
void correlate( FFT_DATA s1, FFT_DATA s2, FFT_DATA r )
{
/* Transform both images */
fourier( s1 );
fourier( s2 );
/* Perform the correlation */
correlate_spectrums( s1, s2, r );
}
/*=============================================================================
** corelation_peak
**-----------------------------------------------------------------------------
**
** Purpose : Search for corelation peak in the corelation data
**
**-----------------------------------------------------------------------------
**
** Entry : Corelation result
**
** Output :
**
**=============================================================================
*/
void corelation_peak( FFT_DATA result, CORRELATION_PEAK *peak )
{
u_short x, y, c;
double sum, module_max, module_min;
double xp, yp, s_x2, s_y2;
u_long nb_pixel;
REAL r;
assert( peak != NULL );
for( c = 0; c < result.nplanes; c++ )
{
/* Search for min and max */
module_max = 0.0;
module_min = HUGE;
for( y = 0; y < result.h; y++ )
{
for( x = 0; x < result.w; x++ )
{
r = *colorValue(result,x,y,c);
if ( r > module_max )
module_max = r;
if ( r < module_min )
module_min = r;
}
}
/* Locate the peak as the barycenter of pixels above (max-min)/sqrt(2) */
xp = 0.0;
yp = 0.0;
s_x2 = 0.0;
s_y2 = 0.0;
sum = 0.0;
nb_pixel = 0;
for( y = 0; y < result.h; y++ )
{
for( x = 0; x < result.w; x++ )
{
double module;
r = *colorValue(result,x,y,c);
module = r - module_min;
if ( module > (module_max-module_min)*0.707 )
{
xp += (x-result.w/2)*module;
yp += (y-result.h/2)*module;
s_x2 += (x-result.w/2)*(x-result.w/2)*module;
s_y2 += (y-result.h/2)*(y-result.h/2)*module;
sum += module;
nb_pixel++;
}
}
}
/* Present the results */
xp /= sum;
yp /= sum;
peak[c].val = module_max - module_min;
peak[c].x = xp;
peak[c].y = yp;
peak[c].sigma_x = sqrt(s_x2/sum - xp*xp);
peak[c].sigma_y = sqrt(s_y2/sum - yp*yp);
}
}
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