CPU Usage (optical flow)

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Hello,

I want to detect faces with OpenCV and apply an optical flow to follow the face. My code works but it is expensive for the CPU (the CPU runs at 20%).

I capture an image at with "capture >> frame" (which gives a new image at each 30ms). Running only this requires 5% of the CPU. However, if I add the code for optical flow "cv::calcOpticalFlowPyrLK(prevGray, gray, prevPoints, currPoints, status, err, winSize, 3, termcrit, 0, 0.001);", running the program leads to a constant CPU usage of 20% for the program. I would very much like to reduce this CPU usage even if my program takes more time to operate.

cv::setNumThreads(2) helps a lot (CPU 10%) but I would like to see other possible methods to optimize.

Here is the code I use (the feature points for the optical flow are pre-generated to simplify the code):

Thank you so much !

Alex

int main(int argc, char *argv[])
{
//cv::setNumThreads(2);

cv::Mat frame;
cv::Mat frametemp;
cv::Mat gray;
cv::Mat prevGray;
cv::vector<cv::Point2f> prevPoints;

cv::vector<uchar> status;
cv::vector<float> err;

cv::VideoCapture capture(0);

float landmarks[68][2];

while (true)
{
    capture >> frame;
    if (!frame.empty())
    {
        for (int i = 0; i < 68; i++)
        {
            landmarks[i][0] = i*5;
            landmarks[i][1] = i*5;
        }

            frame.copyTo(frametemp);
            cvtColor(frametemp, gray, cv::COLOR_BGR2GRAY);
            if (prevGray.empty())
            {
                gray.copyTo(prevGray);
            }

            cv::vector<cv::Point2f> currPoints;

            for (int k = 0; k < 68; k++)
            {
                currPoints.push_back(cv::Point2f(landmarks[k][0], landmarks[k][1]));
            }

            if (!prevPoints.empty())
            {
                cv::calcOpticalFlowPyrLK(prevGray, gray, prevPoints, currPoints, status, err, winSize, 3, termcrit, 0, 0.01);
            }

            std::swap(currPoints, prevPoints);
            cv::swap(prevGray, gray);
    }
    else
    {
        printf(" --(!) No captured frame -- Break!"); break;
    }
    //Sleep(3);
}

return 0;
}