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"

using namespace cv;

namespace
{
    // windows and trackbars name
    const std::string windowName = "Hough Circle Detection Demo";
    const std::string cannyThresholdTrackbarName = "Canny threshold";
    const std::string accumulatorThresholdTrackbarName = "Accumulator Threshold";

    // initial and max values of the parameters of interests.
    const int cannyThresholdInitialValue = 200;
    const int accumulatorThresholdInitialValue = 50;
    const int maxAccumulatorThreshold = 200;
    const int maxCannyThreshold = 255;

    void HoughDetection(const Mat& src_gray, const Mat& src_display, int cannyThreshold, int accumulatorThreshold)
    {
       // will hold the results of the detection
       std::vector<Vec3f> circles;
       // runs the actual detection
       HoughCircles( src_gray, circles, HOUGH_GRADIENT, 1, src_gray.rows/8, cannyThreshold, accumulatorThreshold, 0, 0 );

       // clone the colour, input image for displaying purposes
       Mat display = src_display.clone();
       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( display, center, 3, Scalar(0,255,0), -1, 8, 0 );
            // circle outline
            circle( display, center, radius, Scalar(0,0,255), 3, 8, 0 );
       }

       // shows the results
       imshow( windowName, display);
    }
}


int main(int, 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, COLOR_BGR2GRAY );

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

    //declare and initialize both parameters that are subjects to change
    int cannyThreshold = cannyThresholdInitialValue;
    int accumulatorThreshold = accumulatorThresholdInitialValue;

    // create the main window, and attach the trackbars
    namedWindow( windowName, WINDOW_AUTOSIZE );
    createTrackbar(cannyThresholdTrackbarName, windowName, &cannyThreshold,maxCannyThreshold);
    createTrackbar(accumulatorThresholdTrackbarName, windowName, &accumulatorThreshold, maxAccumulatorThreshold);

    // inifinite loop to display
    // and refresh the content of the output image
    // unti the user presses q or Q
    int key = 0;
    while(key != 'q' && key != 'Q')
    {
        // those paramaters cannot be =0
        // so we must check here
        cannyThreshold = std::max(cannyThreshold, 1);
        accumulatorThreshold = std::max(accumulatorThreshold, 1);

        //runs the detection, and update the display
        HoughDetection(src_gray, src, cannyThreshold, accumulatorThreshold);

        // get user key
        key = waitKey(10);
    }

    return 0;
}