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Something like this should work :

    Mat img=imread("g:/lib/opencv/samples/data/lena.jpg",IMREAD_GRAYSCALE);
    Mat imBin;
    threshold(img,imBin,180,255,THRESH_BINARY);
    imshow("Result", imBin);
    waitKey();
    Mat stats, centroids, labelImage;
    int nLabels = connectedComponentsWithStats(imBin, labelImage, stats, centroids, 8, CV_32S);
    Mat mask(labelImage.size(), CV_8UC1, Scalar(0));
    for (int i = 1; i < nLabels; i++) // 0 is background  may be you should scan it
    {
            int s= stats.at<int>(i, 4);
            cout<<s<<"\t";;
        if (stats.at<int>(i, 4) > 2000)
        {
            mask = mask | (labelImage==i);
        }
    }
    Mat r(img.size(), CV_8UC1, Scalar(0));
    img.copyTo(r,mask);
    imshow("Result", r);
    waitKey();

Something like this should work :

    Mat img=imread("g:/lib/opencv/samples/data/lena.jpg",IMREAD_GRAYSCALE);
    Mat imBin;
    threshold(img,imBin,180,255,THRESH_BINARY);
    imshow("Result", imBin);
    waitKey();
    Mat stats, centroids, labelImage;
    int nLabels = connectedComponentsWithStats(imBin, labelImage, stats, centroids, 8, CV_32S);
    Mat mask(labelImage.size(), CV_8UC1, Scalar(0));
    for (int i = 1; i < nLabels; i++) // 0 is background  may be you should scan it
    {
            int s= stats.at<int>(i, 4);
            cout<<s<<"\t";;
        if (stats.at<int>(i, 4) > 2000)
2000) // 2000 is surface threshold
        {
            mask = mask | (labelImage==i);
        }
    }
    Mat r(img.size(), CV_8UC1, Scalar(0));
    img.copyTo(r,mask);
    imshow("Result", r);
    waitKey();

Something like this should work :

    Mat img=imread("g:/lib/opencv/samples/data/lena.jpg",IMREAD_GRAYSCALE);
    Mat imBin;
    threshold(img,imBin,180,255,THRESH_BINARY);
    imshow("Result", imBin);
    waitKey();
    Mat stats, centroids, labelImage;
    int nLabels = connectedComponentsWithStats(imBin, labelImage, stats, centroids, 8, CV_32S);
    Mat mask(labelImage.size(), CV_8UC1, Scalar(0));
    Mat surfSup=stats.col(4)>2000;

    for (int i = 1; i < nLabels; i++) // 0 is background  may be you should scan it
i++)
    {
            int s= stats.at<int>(i, 4);
            cout<<s<<"\t";;
        if (stats.at<int>(i, 4) > 2000) // 2000 is surface threshold
(surfSup.at<uchar>(i, 0))
        {
            mask = mask | (labelImage==i);
        }
    }
    Mat r(img.size(), CV_8UC1, Scalar(0));
    img.copyTo(r,mask);
    imshow("Result", r);
    waitKey();