Problem to find contours

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I have problem to find contours. There are errors when show the countours. I must change some parameters?

The code:

    imageInput = imread(PATH+images[i], CV_LOAD_IMAGE_COLOR);
    fileOutput <<"Immagine: "<< images[i]<<"\n";


    //verifico l'esistenza dell'immagine
    if(! imageInput.data )
    {
        cout <<  "Impossibile aprire l'immagine" << std::endl ;
        return -1;
    }


    //RGB->Livelli di grigio....necessario per OTSU
   cvtColor( imageInput, imageInputGray, CV_BGR2GRAY );


    //applico OTSU
    // CV_THRESH_BINARY | CV_THRESH_OTSU per questioni di ottimizzazioni
    double otsu_thresh_val= threshold( imageInputGray, imageAfterOtsu, 0, 255, CV_THRESH_BINARY | CV_THRESH_OTSU );
    //applico 4 volte un filtro mediano 3x3 per risolvere il problema della 'polvere'
    medianBlur(imageAfterOtsu, imageAfterMedianBlur, 3);
    medianBlur(imageAfterMedianBlur, imageAfterMedianBlur, 3);
    medianBlur(imageAfterMedianBlur, imageAfterMedianBlur, 3);
    medianBlur(imageAfterMedianBlur, imageAfterMedianBlur, 3);


    //labeling
    int thresh = 0;
    int max_thresh = 255;
    RNG rng(12345);



    vector<vector<Point> > contours;
    vector<Vec4i> hierarchy;


    double high_thresh_val  = otsu_thresh_val,
  lower_thresh_val = otsu_thresh_val * 0.33;

    /// Detect edges using canny
    Canny( imageAfterMedianBlur, imageAfterCanny, lower_thresh_val, high_thresh_val, 3 );
     /// Find contours
    findContours( imageAfterCanny, contours, hierarchy,  CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );

    /// Draw contours
      Mat drawing = Mat::zeros( imageAfterCanny.size(), CV_8UC3 );
      for( int j = 0; j< contours.size(); j++ )
         {
           Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
           drawContours( drawing, contours, j, color, 1, 8, hierarchy, 0, Point() );
           cout<<hierarchy[j][0]<<"  "<<hierarchy[j][1]<<"  "<<hierarchy[j][2]<<"  "<<hierarchy[j][3]<<endl;

         }
    cout<<"---------"<<endl;

The image's result: