Image transformation in OpenCV and Qt C++

Question

I have set of images taken from right side of object like image1. I need to rotate it about vertical axis and change it tobe like image2.

Is that affine transformation useful to convert image1 to image2 ? I used affine transform and played with it, but didn't get desired results. What should I do? I used this part of code for image transformation.

    cv::Mat shearedImage;
cv::Point2f srcPoints[3] = {cv::Point2f(0, 0), cv::Point2f(resizedImage.cols, 0), cv::Point2f(0, resizedImage.rows)};
cv::Point2f dstPoints[3] = {cv::Point2f(0, 0), cv::Point2f(resizedImage.cols, 0), cv::Point2f(0, resizedImage.rows)};
cv::Mat transformMatrix = cv::getAffineTransform(srcPoints, dstPoints);
cv::warpAffine(resizedImage, shearedImage, transformMatrix, resizedImage.size());

Here is the complete code in Qt

    #include "mainwindow.h"
    #include <QApplication>
    #include <opencv2/opencv.hpp>
    #include <QDebug>
    #include <QLabel>
    int main(int argc, char* argv[])
    {
        QApplication a(argc, argv);

    // Load the original image
    cv::Mat originalImage = cv::imread("Pic1.jpg");

    // Crop the image
    cv::Rect roi(200, 300, 1350, 850);
    cv::Mat croppedImage = originalImage(roi);

    // Resize the cropped image
    cv::Mat resizedImage;
    cv::resize(croppedImage, resizedImage, cv::Size(), 0.4, 0.4);

    // Shear the resized image
    cv::Mat shearedImage;
    cv::Point2f srcPoints[3] = {cv::Point2f(0, 0), cv::Point2f(resizedImage.cols, 0), cv::Point2f(0, resizedImage.rows)};
    cv::Point2f dstPoints[3] = {cv::Point2f(0, 0), cv::Point2f(resizedImage.cols, 0), cv::Point2f(0, resizedImage.rows)};
    cv::Mat transformMatrix = cv::getAffineTransform(srcPoints, dstPoints);
    cv::warpAffine(resizedImage, shearedImage, transformMatrix, resizedImage.size());

           // Display the shear image
    cv::namedWindow("Transformed Image");
    cv::imshow("Transformed Image", shearedImage);

    MainWindow w;
    w.show();
    return a.exec();
}

Answer 1

I searched more and found more details, based on this Question, I should use cv::warpPerspective instead of affine transform to change the image perspective.

here is the output and code:

    #include "mainwindow.h"
    #include <QApplication>
    #include <opencv2/opencv.hpp>
    #include <QDebug>
    #include <QLabel>
    
    cv::Point2f srcPoints[4];
    int pointCounter = 0;
    
/*using mouseCallback function to selecting 4 points by left click for changing image perspective.*/
    void mouseCallback(int event, int x, int y, int flags, void* userdata)
    {
        if (event == cv::EVENT_LBUTTONDOWN && pointCounter < 4)
        {
            srcPoints[pointCounter] = cv::Point2f(x, y);
            pointCounter++;
            qDebug() << "Selected point: (" << x << ", " << y << ")";
        }
    }
    
    int main(int argc, char* argv[])
    {
        QApplication a(argc, argv);
    
        // Load the original image
        cv::Mat Image = cv::imread("image1.jpg");
        if (Image.empty())
        {
            qDebug() << "Failed to load image";
            return -1;
        }
    
        // Resize the cropped image
        cv::Mat originalImage;
        cv::resize(Image, originalImage, cv::Size(), 0.9, 0.9);
    
        // Create a window to display the image
        cv::namedWindow("Original Image");
        cv::imshow("Original Image", originalImage);
    
        // Set mouse callback
        cv::setMouseCallback("Original Image", mouseCallback);
    // Display instructions to the user
//    cv::putText(originalImage, "Select points from left to right and clockwise", cv::Point(10, 30),
//                cv::FONT_HERSHEY_SIMPLEX, 1, cv::Scalar(0, 0, 255), 2);
    cv::imshow("Original Image", originalImage);
    
        // Wait until 4 points are selected
        while (pointCounter < 4)
        {
            char key = cv::waitKey(10);
            if (key == 27)  // Esc key
            {
                qDebug() << "Selection aborted";
                return 0;
            }
        }
        cv::destroyWindow("Original Image");
    
        // Generate the perspective transform matrix
        cv::Point2f dstPoints[4] = {cv::Point2f(0, 0), cv::Point2f(originalImage.cols, 0), cv::Point2f(originalImage.cols, originalImage.rows), cv::Point2f(0, originalImage.rows)};
        cv::Mat perspectiveMatrix = cv::getPerspectiveTransform(srcPoints, dstPoints);
    
        // Apply the perspective transform
        cv::Mat transformedImage;
        cv::warpPerspective(originalImage, transformedImage, perspectiveMatrix,  originalImage.size());
    
        // Display the transformed image
        cv::namedWindow("Transformed Image");
        cv::imshow("Transformed Image", transformedImage);
    MainWindow w;
        w.show();
        return a.exec();
    }