opencv/samples/cpp/tutorial_code/ImgTrans/HoughCircle_Demo.cpp

/**
 * @file HoughCircle_Demo.cpp
 * @brief Demo code for Hough Transform
 * @author OpenCV team
 */

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>

using namespace cv;

/**
 * @function main
 */
int main(int argc, char** argv)
{
   Mat src, src_gray;

   /// Read the image
   src = imread( argv[1], 1 );

   if( !src.data )
     { return -1; }

   /// Convert it to gray 
    cvtColor( src, src_gray, CV_BGR2GRAY );

   /// Reduce the noise so we avoid false circle detection
    GaussianBlur( src_gray, src_gray, Size(9, 9), 2, 2 );

    vector<Vec3f> circles;

   /// Apply the Hough Transform to find the circles
    HoughCircles( src_gray, circles, CV_HOUGH_GRADIENT, 1, src_gray.rows/8, 200, 100, 0, 0 );

   /// Draw the circles detected
    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]);
         // circle center
         circle( src, center, 3, Scalar(0,255,0), -1, 8, 0 );
         // circle outline
         circle( src, center, radius, Scalar(0,0,255), 3, 8, 0 );
    }

   /// Show your results 
    namedWindow( "Hough Circle Transform Demo", CV_WINDOW_AUTOSIZE );
    imshow( "Hough Circle Transform Demo", src );

    waitKey(0);
    return 0;
}