OpenCV图像色彩空间转换

QString appPath = QCoreApplication::applicationDirPath();
  imagePath = appPath + "/sun.png";
  img = cv::imread(imagePath.toStdString());
  if (img.empty())
    return;
  imshow("img", img);
  cv::Mat hsv;
  cv::cvtColor(img,hsv,COLOR_BGR2HSV);
  cv::Mat mask;
  inRange(hsv, Scalar(0,0,221), Scalar(180,30,255), mask);
  Mat redback = Mat::zeros(img.size(), img.type());
  redback = Scalar(40, 40, 200);
  bitwise_not(mask, mask);
  imshow("mask", mask);
  img.copyTo(redback, mask);
  imshow("roi", redback);