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Calculating sum using integral image

asked 2013-03-24 22:06:51 -0500

updated 2013-03-24 22:11:17 -0500

I am attempting to calculate sums over rectangular areas in images using the Viola & Jones trick with the integral image.

Im using c++ and the cv::Mat class.

Here is what I am doing:

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    integral(Img,M);

    CvRect region;

    region.x=0; 
    region.y=0; 
    region.width=Img.cols;
    region.height=Img.rows; //calculating sum on entire image


      double regionSum;

      int tl= IntegralImage.at<double>((region.y),(region.x));
      int tr= IntegralImage.at<double>((region.y),(region.x+region.width+1));
      int bl= IntegralImage.at<double>((region.y+region.height+1),(region.x));
      int br= IntegralImage.at<double>((region.y+region.height+1),(region.x+region.width+1));

      regionSum = br-bl-tr+tl;

      cout<<"tl: "<<tl<<" tr: "<<tr<<" bl: "<<bl<<" br: "<<br<<" sum: "<<regionSum<<endl;

For some images those parameters output zero, for others there is a result but that doesn't really make sense, so obviously I am doing something wrong-

Thanks in advance.

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answered 2013-03-25 02:02:54 -0500

berak gravatar image

your integral img has int type(by default), you're accessing it as double.

so either specify the right type:

integral(img,isum,CV_64F); // omitting the type param makes an int image

or access it as int:

isum.at<int>(row,col);
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Comments

THANKS! This help me a lot!

IKS gravatar imageIKS ( 2014-07-23 02:50:01 -0500 )edit
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Asked: 2013-03-24 22:06:51 -0500

Seen: 8,842 times

Last updated: Mar 25 '13