std::string img_path = vm["img-path"].as<std::string>();

    // schedule image loading on the opencv pool
    hpx::future<cv::Mat> f_image = hpx::async(opencv_executor, &load_image,
            img_path);

    // schedule image show on the opencv pool
    hpx::future<void> f_imshow = hpx::async(opencv_executor, &show_image,
                                            f_image.get());

    cv::Mat grey_image;
    //schedule image processing on the default pool
    hpx::future<bool> f_img_process = hpx::async(normal_priority_executor,
            &transform_to_grey, f_image.get(), grey_image);

    f_img_process.get();

    // schedule image show on the opencv pool
    hpx::future<void> f_imshow_grey = hpx::async(opencv_executor, &show_image,
                                            grey_image);