OpenCV - 摄像头读取图像

VideoCapture cap(1); // try to open the USB camera
const string windowName = "Realtime Image";
bool isRunning = true;
if (!cap.isOpened())  // check if we succeeded
{
	cap.open(0);// try to open the default camera if USB camera failed
	if (!cap.isOpened())
	{
		cout << "No Camera Found!" << endl;
		return -1;
	}
}
Mat frame;	
cap >> frame;
if (frame.empty())
{
	cout << "The frame is empty !!!" << endl;
	return -1;
}        
namedWindow(windowName, 1);       
while (isRunning)
{
	Mat frame;
	cap >> frame; // get a new frame from camera
	imshow(windowName, frame);		
	int key = waitKey(1000);
	switch (key)
	{
	case 27:
		isRunning = false;
		break;
	default:
		break;
	}
}