How to link opencv in QtCreator and use Qt library

Configuring and using OpenCV in Qt Creator involves multiple steps, requiring the correct setup of include paths, library paths, and other compilation options within the Qt project. Here is a detailed guide for linking and using OpenCV in Qt Creator:

Step 1: Installing OpenCV

First, install the OpenCV library on your machine. You can download precompiled binaries from the OpenCV website or compile from source. For Windows, download precompiled binaries; for Linux or macOS, it is generally recommended to compile from source to ensure optimal compatibility.

Step 2: Creating a Qt Project

Create a new Qt Widgets Application in Qt Creator. During creation, select the appropriate Qt version and build configuration.

Step 3: Configuring the Project File (.pro)

Open your project file (.pro) in Qt Creator and add the necessary OpenCV libraries. You need to specify the include directory and library directory for OpenCV. Below is a configuration example, assuming OpenCV is installed at C:/opencv/build:

pro
INCLUDEPATH += C:/opencv/build/include

LIBS += -LC:/opencv/build/x64/vc15/lib \n        -lopencv_core410 \n        -lopencv_imgproc410 \n        -lopencv_highgui410 \n        -lopencv_imgcodecs410

Note: Depending on your OpenCV version and compiler, the library names and paths may vary. For example, the 410 in the above indicates OpenCV version 4.1.0; adjust accordingly if your version differs.

Step 4: Writing Code

Now you can start using OpenCV in your Qt project. Here is a basic example demonstrating how to read an image in Qt, process it using OpenCV, and display the processed image in a Qt QLabel:

cpp
#include <QLabel>
#include <QImage>
#include <QPixmap>
#include <opencv2/opencv.hpp>

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

    // Use OpenCV to load the image
    cv::Mat image = cv::imread("path_to_image.jpg", cv::IMREAD_COLOR);
    if(image.empty())
        return -1;

    // Convert OpenCV's Mat to QImage
    QImage imgIn= QImage((uchar*) image.data, image.cols, image.rows, image.step, QImage::Format_RGB888);

    // Create QLabel to display the image
    QLabel label;
    label.setPixmap(QPixmap::fromImage(imgIn));
    label.show();

    return app.exec();
}

Step 5: Compiling and Running

Compile and run your application in Qt Creator. If everything is set up correctly, you should see the loaded image displayed in your Qt application.

Notes

• Ensure that both Qt and OpenCV are compiled with the same compiler; otherwise, you may encounter linking errors.
• When adding library files, ensure that the paths and library version numbers are correct.

By following these steps, you should be able to successfully configure and use OpenCV in Qt Creator. This process involves some configuration work, but once set up, you can fully leverage the powerful features of both Qt and OpenCV.