cv::Mat webcam_img;
    cv::Mat grey_webcam_img;
    // schedule taking webcam image on the opencv pool
    hpx::future<cv::Mat> f_image =
            webcam_closed.then([&](hpx::future<int>&& wc){
                hpx::cout << "Webcam closed\n";
                return hpx::async(opencv_executor, &take_webcam_image);
            });

    // schedule transforming webcam image to grey-scale on opencv pool
    hpx::future<cv::Mat> f_grey_image =
            f_image.then([&](hpx::future<cv::Mat>&& fi){
                hpx::cout << "Image taken\n";
                webcam_img = fi.get();
                return hpx::async(opencv_executor, &transform_to_grey,
                                  webcam_img);
            });

    f_grey_image.then([&](hpx::future<cv::Mat>&& fgi){
            hpx::cout << "Image transformed to grey\n";
            grey_webcam_img = fgi.get();
            return hpx::async(opencv_executor, &save_image, grey_webcam_img, "");
        });