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Identify Pepperoni Slice: Houghs Circles is Slow


I am making a simple fun project that identifies how many pepperoni pieces/slices are on a pizza. The algorithm to count the no. of pepperoni slices is based off this example and is as follows:

  • For each video frame:
    • Convert to gray scale
    • Apply Gaussian Blur to reduce noise
    • Use Hough's Circle to identify all pepperoni slices and the pizza itself
    • If a circle sits inside another circle (pizza): then its a pepperoni slice

Example of the frame input: image description

The execution of the program is incredibly slow (as in 1 frame per second) and the algorithm is very hit and miss. Can you provide advice on why its slow, how I can achieve any speed increases and improve/alternative algorithms? Should I identify slices by their colour instead?


while (true) {

    if (!
    return -1;

    vector <Vec3f> circles;
    IdentifyCircles(gCameraFeed, circles);
    DrawPepperoni(gCameraFeed, circles);

    imshow(MAIN_WND_TITLE, gCameraFeed);

    // Exit on escape key down
    int c = waitKey(30);
    if ((char)c == 27)

int IdentifyCircles(const Mat& frame, vector<Vec3f>& circles)
    // Post: Use Hough Circles algorithm to identify all circles in frame

    Mat grayScaleFrame;

    cvtColor(frame, grayScaleFrame, CV_BGR2GRAY);
    GaussianBlur(grayScaleFrame, grayScaleFrame, Size(9, 9), 2, 2);
    HoughCircles(grayScaleFrame, circles, CV_HOUGH_GRADIENT, 1, grayScaleFrame.rows/8, 50, 50, 0, 0);
    putText(gCameraFeed, "Circles Identified: " + to_string(circles.size()), Point(20, 50), 1, 2, Scalar::all(200), 1, 8);

    return 1;