CODEWITHSUNDEEP
c++opencvvectorstdopencv3.0
Amarula
Amarula

Reputation: 162

OpenCV placing the same image into the container

I am trying to write a programm that captures n frames from the video and places them into the container for further work (I'm making a collage afterwards). But i've encountered an issue, when all images in the container are the same(it is filled only with last image captured). I've checked that images are captured correctly, as I'm saving them as well and can cleary see that they are different.

Here is my code:

std::vector<cv::Mat> MY_framelist; //container for captured frames

cv::VideoCapture myvid; 
cv::Mat MY_frame; //will capture frames here
myvid.open(pass_filename); //open video file(char* pass_filename=12.mp4)

if (!myvid.isOpened()) {
    printf("Capture not open \n");
}

double x_length = myvid.get(CV_CAP_PROP_FRAME_COUNT); //get maxlength of the video

uint each_frame = uint(x_length) / 16; //capture every 16 frames

    for (uint j = 0, current_frame = 1; (current_frame < x_length) && (j < 16); current_frame += each_frame, j++)
{

        myvid.set(CV_CAP_PROP_POS_FRAMES, current_frame); //set frame
        myvid.read(MY_frame);  // then capture the next one
        MY_framelist.push_back(MY_frame); //place it into the container


        std::stringstream frameNum; //generating name for saved images
        frameNum << j + 1;
        if (j + 1 <= 9)
            my_filename += "0";
        my_filename += frameNum.str();
        my_filename += ".jpg";

        cv::imwrite(my_filename.c_str(), MY_frame); //saving images to prove that they are captured correctly

        my_filename = "test";

        printf(" and Image # ");
        printf("%d", j + 1);
        printf(" saved \n");

    }

As a result MY_framelist will contain 16 same images that were captured last. What am I doing wrong here? I've seen some workarround here , but I'm not really eager to do this as it will lead to not so accurate results. Thanks in advance!

Upvotes: 1

Views: 186

Answers (1)

Miki
Miki

Reputation: 41765

OpenCV Mat copy is a shallow copy, i.e. only the header is copied, not the data. So here:

MY_framelist.push_back(MY_frame); //place it into the container

you'll get a container with always the same image.

You need to do a deep copy copying the data, too:

MY_framelist.push_back(MY_frame.clone()); //place it into the container

Upvotes: 1

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