Converting Live Video Frames to Grayscale (OpenCV) - c++

Question

First and foremost, I should say that I'm a beginner to OpenCV. I'm trying to convert a live video stream from my webcam from RGB to Grayscale.
I have the following code in my function:
VideoCapture cap(0);
while (true)
{
Mat frame;
Mat grayscale;
cvtColor(frame, grayscale, CV_RGB2GRAY);
imshow("Debug Window", grayscale);
if (waitKey(30) >=0)
{
cout << "End of Stream";
break;
}
}
I know it isn't complete. I'm trying to find a way to take a frame of the video and send it to frame, manipulate it using cvtColor, then output it back to grayscale so I can display it on my screen.
If anyone could help, it would be much appreciated.

Answer 1

Please see this example, here the complete code exists, hope this will work for you:
#include "opencv2/highgui/highgui.hpp"
#include <iostream>
using namespace cv;
using namespace std;
int main(int argc, char* argv[])
{
VideoCapture cap(0); // open the video camera no. 0
if (!cap.isOpened()) // if not success, exit program
{
cout << "Cannot open the video cam" << endl;
return -1;
}
namedWindow("MyVideo",CV_WINDOW_AUTOSIZE);
while (1)
{
Mat frame;
bool bSuccess = cap.read(frame); // read a new frame from video
if (!bSuccess)
{
cout << "Cannot read a frame from video stream" << endl;
break;
}
Mat grayscale;
cvtColor(frame, grayscale, CV_RGB2GRAY);
imshow("MyVideo", grayscale);
if (waitKey(30) == 27)
{
cout << "esc key is pressed by user" << endl;
break;
}
}
return 0;
}

Answer 2

You just initialized the variable "frame" and forgot to assign an image to it. Since the variable "frame" is empty you won't get output. Grab a image and copy to frame from the video sequence "cap". This piece of code will do the job for you.
Mat frame;
bool bSuccess = cap.read(frame); // read a frame from the video
if (!bSuccess)
{
cout << "Cannot read a frame from video stream" << endl;
break;
}