将实时视频帧转换为灰度（OpenCV）

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;
    }