@Override
  protected void setup() {
    // open camera and set resolution
    cam = new VideoCapture();
    cam.open(camId);
    cam.set(Videoio.CV_CAP_PROP_FRAME_WIDTH, camWidth);
    cam.set(Videoio.CV_CAP_PROP_FRAME_HEIGHT, camHeight);

    // check if camera is open
    if (!cam.isOpened()) {
      throw new IllegalStateException("Couldn't open cam: " + camId);
    }
  }
 @Override
 protected void shutdown() {
   System.out.println("Shutdown cam " + camId);
   cam.release();
   while (cam.isOpened()) {}
 }