CODEWITHSUNDEEP
c++multithreadingopencv
Siddharth
Siddharth

Reputation: 1

Main function skipping thread and not joining to show the desired output

The function ProcessFrames takes in one quadrant of the image, and applies a Canny Filter to it. But the thread created does not give out a Canny detected image. instead, I get the color quadrant of the image in imshow().

void ProcessFrames(Mat &image)
{
    Mat test = image;
    Canny(test, image, 5, 60, 3);
}

void main()
{
    Mat frame;
    Mat top_left, top_right, bot_left, bot_right;
    String filename = "C:\\Users\\operator\\Downloads\\MODFAM1080I.mpg";
    VideoCapture capture(filename);
    if (!capture.isOpened())
        throw "Error when reading video file!!";
    while (1)
    {
        capture >> frame;
        if (frame.empty())
        break;
        top_left = frame(Range(0, frame.rows / 2 - 1), Range(0, frame.cols / 2 - 1));
        top_right = frame(Range(0, frame.rows / 2 - 1), Range(frame.cols / 2, frame.cols - 1));
        bot_left = frame(Range(frame.rows / 2, frame.rows - 1), Range(0, frame.cols / 2 - 1));
        bot_right = frame(Range(frame.rows / 2, frame.rows - 1), Range(frame.cols / 2, frame.cols - 1));
        //Cropping the image into four quadrants to process it separately. 
        thread t1(ProcessFrames,top_left); //invoking a thread and passing first quadrant.
        t1.join(); //joing the thread with the main function
        imshow("Canny", top_left); // still shows color image of the first quadrant. Canny not reflected.
        cvWaitKey(10);
    }
}

Upvotes: 0

Views: 96

Answers (1)

Petar Velev
Petar Velev

Reputation: 2355

std::thread constructor copies everything. If you want to pass data pointer and this data to be changed in the thread you must wrap it with std::ref().

Upvotes: 2

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