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I want to stitch 2 images by crosscorrelation measure, but I don't want to use fft.

I tryed this but something seems to be wrong.any suggestions?

void test(IplImage* src,IplImage* temp)
{
double max_peak=0;
                Point pt;
                double per_x=0.5;
                double per_y=0.5;
                for(int cy=-h*per_y;cy<h*per_y;++cy)
                {
                        for(int cx=-w*per_x;cx<w*per_x;++cx)
                        {
                                uchar* s_p= (uchar*) src->imageData;
                                uchar* t_p= (uchar*) temp->imageData;
                                __int64 suma=0;
                                __int64 sumb=0;
                                for(int y=0;y<h;++y)
                                {
                                        for(int x=0;x<w;++x)
                                        {
                                                suma+= s_p[x];
                                                if((y+cy)<h&&(x+cx)<w&&
                                                        (y+cy)>0&&(x+cx)>0)
                                                        sumb+= t_p[x+cx];
                                        }
                                        s_p+=w;
                                        t_p+=w;
                                }
                                int meana = (int)(suma / (w * h)),
                                        meanb = (int)(sumb / (w * h)); 


                                s_p= (uchar*) src->imageData;
                                t_p= (uchar*) temp->imageData;

                                __int64 corr = 0,
                                        denoma = 0,
                                        denomb = 0;

                                for(int y=0;y<h;++y)
                                {
                                        for(int x=0;x<w;++x)
                                        {
                                                int da = (int)s_p[x] - meana;
                                                int db= 0;
                                                if((y+cy)<h&&(x+cx)<w&&
                                                        (y+cy)>0&&(x+cx)>0)
                                                        db = (int)t_p[x+cx] - meanb; 
                                                else
                                                        db= -meanb;

                                                corr += da * db;
                                                denoma += da * da;
                                                denomb += db * db;
                                        }
                                        s_p+=w;
                                        t_p+=w;
                                }

                                double peak= corr / sqrt( (double)denoma * denomb);
                                if (peak>max_peak)
                                {
                                        pt.x= cx;
                                        pt.y= cy;
                                        max_peak=peak;
                                }
                        }
                }  
}
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2 Answers 2

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At the start of the inner loop, you assign

uchar* t_p= (uchar*) temp->imageData;

later on, you use it as

t_p[x+cx];

Aren't you missing the cy here?

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Isn't that what the following function in OpenCV does? Be sure to check out the method param.

void cvMatchTemplate(const CvArr* image, const CvArr* templ, CvArr* result, int method)

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  • $\begingroup$ cvMatchTemplate use DFT, I need to do it without fft. $\endgroup$
    – mrgloom
    Commented Dec 12, 2012 at 9:35
  • 2
    $\begingroup$ Why would you not want to use FFT? Its just a faster implementation of DFT and shows no performance or quality loss. Is this a homework problem? $\endgroup$
    – Naresh
    Commented Dec 12, 2012 at 9:56
  • $\begingroup$ hmm. Had to go read the source. You are correct it does use fft. Just curious, why is that a limitation? $\endgroup$
    – Zigner
    Commented Dec 12, 2012 at 9:56
  • $\begingroup$ I want to check my fft implementation works just like original implementation and I want to do performance comparision.Also maybe it will be simpler to parallelize code without fft. $\endgroup$
    – mrgloom
    Commented Dec 12, 2012 at 10:10
  • $\begingroup$ @mrgloom Im not sure you will be able to beat doing a correlation without using the FFT. $\endgroup$
    – Spacey
    Commented Dec 13, 2012 at 4:14

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