准备用一个月的时间，系统学习下OpenCV

代码跟着 Learning OpenCV 3: Coumputer Vision in C++ with the OpenCV Library(《学习OpenCV 3》) 这本书来敲

环境：

系统：Ubuntu20LTS
编译：CMake，g++，遵循C++11标准
库：opencv 4.4.0
编辑器：Clion

示例2-2 简单加载并显示图像
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#include <opencv2/opencv.hpp>
#include <opencv2/highgui.hpp>
using namespace cv;

int main(){
    Mat img = imread("");
    if(img.empty())
      return -1;
    namedWindow("Example1", WINDOW_AUTOSIZE);
    imshow("Example1",img);
    waitKey(0);

    destroyWindow("Example1");
    return 0;
}

示例2-2

示例2-5 平滑处理图像
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#include <opencv2/opencv.hpp>
using namespace cv;

int main() {
    Mat image = imread("/home/lushuangning/Pictures/miku1314.jpg");
    namedWindow("example2-5-in", WINDOW_AUTOSIZE);
    namedWindow("example2-5-out", WINDOW_AUTOSIZE);
    imshow("example2-5-in", image);

    Mat out;
    //Could use GaussianBlur(),blur(),medianBlur() or bilateralFilter()
    GaussianBlur(image, out, Size(5,5), 3,3);
    GaussianBlur(out, out,Size(5,5), 3, 3);
    imshow("example2-5-out", out);
    waitKey(0);

    return 0;
}

示例2-5

示例2-6 基2降采样
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#include <opencv2/opencv.hpp>
#include <opencv2/highgui.hpp>
using namespace cv;

int main() {
    Mat img1,img2;
    namedWindow("example1", WINDOW_AUTOSIZE);
    namedWindow("example2", WINDOW_AUTOSIZE);

    img1 = imread("/home/lushuangning/Pictures/miku1314.jpg");
    imshow("example1", img1);
    pyrDown(img1, img2);
    imshow("example2", img2);
    waitKey(0);
    return 0;
}

示例2-6

示例2-7 Canny边缘检测
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#include <opencv4/opencv2/opencv.hpp>
#include <opencv4/opencv2/highgui.hpp>
using namespace cv;

int main(){
    Mat img_rgb, img_gry, img_cny;
    namedWindow("Example Gray",WINDOW_AUTOSIZE);
    namedWindow("Example Canny",WINDOW_AUTOSIZE);

    img_rgb = imread("/home/lushuangning/Pictures/miku1314.jpg");
    //RGB转灰度图
    cvtColor(img_rgb, img_gry, COLOR_BGR2GRAY);
    //对灰度图使用Canny边缘检测
    Canny(img_gry, img_cny, 100, 150, 3, true);

    imshow("Example Gray", img_gry);
    imshow("Example Canny", img_cny);
    waitKey(0);
    return 0;
}

示例2-7

Canny边缘检测论文如下：
A Computational Approach to Edge Detection

挖个坑，待填，尽快读完，用代码复现一遍

示例2-8
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#include <opencv4/opencv2/opencv.hpp>
#include <opencv4/opencv2/highgui.hpp>
using namespace cv;

int main(){
    Mat img_rgb, img_gry, img_cny, img_pyr, img_pyr2;

    namedWindow("Example rgb",WINDOW_AUTOSIZE);
    namedWindow("Example gry",WINDOW_AUTOSIZE);
    namedWindow("Example Canny",WINDOW_AUTOSIZE);
    namedWindow("Example pyr",WINDOW_AUTOSIZE);
    namedWindow("Example pyr2",WINDOW_AUTOSIZE);


    img_rgb = imread("/home/lushuangning/Pictures/miku1314.jpg");
    //RGB转灰度图
    cvtColor(img_rgb, img_gry, COLOR_BGR2GRAY);
    //连续两次基2降采样
    pyrDown(img_gry, img_pyr);
    pyrDown(img_pyr, img_pyr2);
    //使用Canny边缘检测
    Canny(img_pyr2, img_cny, 80, 120, 3, true);

    imshow("Example rgb", img_rgb);
    imshow("Example gry", img_gry);
    imshow("Example pyr", img_pyr);
    imshow("Example pyr2", img_pyr2);
    imshow("Example Canny", img_cny);
    waitKey(0);
    return 0;
}

示例2-9 读取图片中某一位置的像素值
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#include <iostream>
#include <opencv2/opencv.hpp>
#include <opencv2/highgui.hpp>
using namespace cv;
using namespace std;

int main() {
    Mat img,img_gry;
    int x = 16, y = 32;
    img = imread("/home/lushuangning/Pictures/miku1314.jpg");
    cvtColor(img, img_gry, COLOR_BGR2GRAY);
    Vec3b  intensity = img.at<Vec3b>(y, x);
    uchar blue = intensity[0];
    uchar green = intensity[1];
    uchar red = intensity[2];

    cout << "At (" << x << "," << y << "): (blue, green, red) = ("
         << (unsigned int)blue << ", "
         << (unsigned int)green << ", "
         << (unsigned int)red << ")" << endl;

    cout << "Gray pixel there is: "
         << (unsigned int)img_gry.at<uchar>(y, x) << endl;
    return 0;
}
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At (16,32): (blue, green, red) = (246, 245, 235)
Gray pixel there is: 242

(未完待续)