text: #include <opencv2/imgproc.hpp>
  #include <opencv2/highgui.hpp>
  #include <math.h>
  
  using namespace cv;
  using namespace std;
  
  int main(int argc, char** argv)
  {
      Mat img, gray;
      if( argc != 2 || !(img=imread(argv[1], 1)).data)
          return -1;
      cvtColor(img, gray, COLOR_BGR2GRAY);
      // smooth it, otherwise a lot of false circles may be detected
      GaussianBlur( gray, gray, Size(9, 9), 2, 2 );
      vector<Vec3f> circles;
      HoughCircles(gray, circles, HOUGH_GRADIENT,
                   2, gray.rows/4, 200, 100 );
      for( size_t i = 0; i < circles.size(); i++ )
      {
           Point center(cvRound(circles[i][0]), cvRound(circles[i][1]));
           int radius = cvRound(circles[i][2]);
           // draw the circle center
           circle( img, center, 3, Scalar(0,255,0), -1, 8, 0 );
           // draw the circle outline
           circle( img, center, radius, Scalar(0,0,255), 3, 8, 0 );
      }
      namedWindow( "circles", 1 );
      imshow( "circles", img );
  
      waitKey(0);
      return 0;
  }
  