OpenCV learning (1): image reading and display and setting of mouse click events

Personal notes when learning OpenCV, for the convenience of netizens and myself to check, the following records are now made:

Go directly to the code:

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>

#include <iostream>

using namespace std;
using namespace cv;

// Declare the method to be called in advance
void onMouse(int event, int x, int y, int flgs, void* param);

int main(int atgc, char *argv[]){

    cv::Mat image;  // 创建一个空图像
    std::cout << "This image is " << image.rows << " x " << image.cols << std::endl;

    image = cv::imread("E:/earth.jpg");  // 读取图像
    if (image.empty()){
        cout << "read image error!" << endl;
        return 0;
    }

    // Example of flipping an image
    Mat flipImage;
    flip(image, flipImage, 1); // positive number means horizontal, 0 means vertical, negative number means horizontal and vertical

    // File read and write operations
    //imwrite("E:/flipImage.jpg", flipImage);

    // Read an image and convert it to grayscale
    Mat grayImage = imread("E:/earth.jpg", CV_LOAD_IMAGE_GRAYSCALE);
    Mat threeChannel = imread("E:/earth.jpg", CV_LOAD_IMAGE_COLOR);
    cout << " All channels :" << threeChannel.channels() << endl;

    // draw graphics or write text on the image
    circle(image,
        Point(122, 110), // center of circle
        65, // radius
        0, // color
        3); // thickness

    putText(image,
        "This is a picture",
        Point(40, 40),
        cv::FONT_HERSHEY_PLAIN, // font type
        2.0, // font size
        255, // font color
        2 // text thickness
        );

    //// Image display
    cvNamedWindow("pic", CV_WINDOW_AUTOSIZE);
    imshow("pic", image);

    cvNamedWindow("pic1", CV_WINDOW_AUTOSIZE);
    imshow("pic1", flipImage);

    // Mouse click time discrimination
    setMouseCallback("pic", onMouse, reinterpret_cast<void*>(&image));

    waitKey(0);

    return 0;
}

// Method implementation
void onMouse(int event, int x, int y, int flgs, void* param){
    Mat *im = reinterpret_cast<Mat*>(param);

    switch (event)
    {
    case CV_EVENT_LBUTTONDOWN: // The trigger callback function of the left mouse button press time
        cout <<"at (" << x << "," << y <<") value is:" << static_cast< int>(im->at<uchar>(Point(x, y))) << endl;
        break;
    }
}

 

Reference: OpenCV computer vision programming strategy