Display Webcam Frames in Qt 6 Application using OpenCV

In today's rapidly evolving technological landscape, integrating computer vision capabilities into graphical user interfaces is becoming increasingly common. One powerful combination for such applications is using the Qt framework along with the OpenCV library. Qt provides a robust and user-friendly interface, while OpenCV offers a comprehensive set of tools for computer vision tasks. This tutorial shows how to display webcam frames in Qt 6 application using OpenCV.

Prepare environment

Ensure that Qt and OpenCV are installed on the system. The vcpkg package manager can be used for an easy installation process

Code

The following steps are performed in the code:

• Using OpenCV, the program initializes the default webcam and configures the frame width and height.
• The QLabel widget is created for displaying the captured frames, and its dimensions are specified.
• The timeout signal of the timer is connected to a lambda function. This function captures a frame from the webcam, converts it to the QImage, and then assigns it as the QPixmap for the associated QLabel.
• The timer is started with a timeout interval corresponding to 30 frames per second.
• Finally, the QLabel is displayed in the application window.

#include <QApplication>
#include <QLabel>
#include <QImage>
#include <QTimer>
#include <opencv2/opencv.hpp>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QSize size(640, 480);

    cv::VideoCapture cap(0);
    cap.set(cv::CAP_PROP_FRAME_WIDTH, size.width());
    cap.set(cv::CAP_PROP_FRAME_HEIGHT, size.height());
    if (!cap.isOpened()) {
        std::cout << "Cannot open webcam" << std::endl;

        return -1;
    }

    auto *imageLabel = new QLabel();
    imageLabel->resize(size);

    cv::Mat frame;
    QTimer timer;
    QObject::connect(&timer, &QTimer::timeout, [&]() {
        cap >> frame;
        QImage qimg(frame.data, frame.cols, frame.rows, frame.step, QImage::Format_BGR888);

        imageLabel->setPixmap(QPixmap::fromImage(qimg));
    });

    timer.start(1000 / 30); // 30 fps
    imageLabel->show();

    return QApplication::exec();
}