在opencv c ++中从相机抓取并保存特定的帧

Question

I have program in opencv with c++ I want to save specific frame from sequence of frames but just last frame is saved! let me introduce better I have the following code :

   Mat frame,img1,img2;
   for(int i = 0; i < 100; i++)
        {
            cout<<i<<endl;
            waitKey(1);
            video >> frame;

            if (i==10)
                {
                    img2=frame;

                }
            namedWindow("img");
            imshow("img",frame);
        }

namedWindow("pic");
imshow("pic",img2);
waitKey(30);
video.release();
waitKey(0);  

as you can see 100 frames are grabbed and I want to save tenth frame in img2 and show it out of for loop when loop is finished but the problem here is that it does not show tenth frame! indeed it shows last frame!

Answer 1

img2 = frame; will perform a copy of the cv::Mat . However, copying a Mat will copy only the header of the Mat , but both objects will refer to the same data. So, if you modify the data of frame , you're also modifying img2 .

What you need is deep copy , ie you want to copy not only the header, but also the data. Doing so, modifying frame won't affect img2 .

You can perform a deep copy simply with:

img2 = frame.clone();