OpenCV访问图像中的像素需要先—— 行，后—— 列

     通过OpenCV访问图像中的像素时，若先访问列再访问行的话，会出现如下错误：

OpenCV(3.4.2) Error: Assertion failed ((unsigned)i0 < (unsigned)size.p[0]) in cv
::Mat::at, file d:\diyprogram\buildopencvvs\install\include\opencv2\core\mat.inl
.hpp, line 1098
OpenCV: terminate handler is called! The last OpenCV error is:
OpenCV(3.4.2) Error: Assertion failed ((unsigned)i0 < (unsigned)size.p[0]) in cv
::Mat::at, file d:\diyprogram\buildopencvvs\install\include\opencv2\core\mat.inl
.hpp, line 1098

若改为先行后列则可正确运行

代码如下：

#include <iostream>
#include <string>
#include <sstream>
using namespace std;

//OpenCV头文件
#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
using namespace cv;

int main( int argc, const char** argv )
{
    //读图像
    Mat color = imread("1.jpg");
    Mat gray = imread("1.jpg", 0);

    //写图像
    imwrite("1Gray.jpg", gray);

    //通过OpenCV函数获取相同像素
    int myRow = color.rows-1;       //访问图像像素是需要先访问行再访问列
    int myCol = color.cols-1;
    Vec3b pixel = color.at<Vec3b>(myRow, myCol);
    cout << "Pixel value (B,G,R): (" << (int)pixel[0] << "," <<
            (int)pixel[1] << (int)pixel[2] << ")" << endl;

    //显示图像
    namedWindow("Lena BGR",WINDOW_NORMAL);
    namedWindow("Lena Gray",WINDOW_NORMAL);
    imshow("Lena BGR", color);
    imshow("Lena Gray", gray);

    //等待按键
    waitKey(0);
    return 0;
}
#include <iostream>
#include <string>
#include <sstream>
using namespace std;

//OpenCV头文件
#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
using namespace cv;

int main( int argc, const char** argv )
{
    //读图像
    Mat color = imread("1.jpg");
    Mat gray = imread("1.jpg", 0);

    //写图像
    imwrite("1Gray.jpg", gray);

    //通过OpenCV函数获取相同像素
    int myRow = color.rows-1;       //访问图像像素是需要先访问行再访问列
    int myCol = color.cols-1;
    Vec3b pixel = color.at<Vec3b>(myRow, myCol);
    cout << "Pixel value (B,G,R): (" << (int)pixel[0] << "," <<
            (int)pixel[1] << (int)pixel[2] << ")" << endl;

    //显示图像
    namedWindow("Lena BGR",WINDOW_NORMAL);
    namedWindow("Lena Gray",WINDOW_NORMAL);
    imshow("Lena BGR", color);
    imshow("Lena Gray", gray);

    //等待按键
    waitKey(0);
    return 0;
}