源码如下：

#include <opencv2/opencv.hpp>
int main(int argc, char** argv)
{
    cv::Mat img_rgb, img_gry, img_cny;
    cv::namedWindow("Example Gray",cv::WINDOW_AUTOSIZE);
    cv::namedWindow("Example Canny", cv::WINDOW_AUTOSIZE);
    img_rgb = cv::imread(argv[1]);
    cv::cvtColor(img_rgb, img_gry, cv::COLOR_BGR2GRAY);  //生成一个和原图一样大小，但只有一个通道的图像，从而将BGR图像转换为灰度值
    cv::imshow("Example Gray", img_gry);
    cv::Canny(img_gry, img_cny, 10, 100, 3, true);
    cv::imshow("Example Canny", img_cny);
    cv::waitKey(0);

    int x = 16, y = 32;
    cv::Vec3b intensity = img_rgb.at<cv::Vec3b>(y, x);
    uchar blue = intensity[0];     //读写像素值 blue
    uchar green = intensity[1];   //读写像素值 green
    uchar red = intensity[2];       //读写像素值 red
    std::cout << "At(x,y)=(" << x << "," << y << "):(blue,green,red)=(" << (unsigned int)blue <<
        "," << (unsigned int)green << "," << (unsigned int)red << ")" << std::endl;
    std::cout <<"Gray pixel there is:" << (unsigned int)img_gry.at<uchar>(y, x) << std::endl;
    x /= 4; y /= 4;
}