1、=

#include <opencv2/opencv.hpp>
using namespace cv;
#include <iostream>
using namespace std;

int main()
{
    Mat img1(300, 300, CV_32FC3, Scalar(1, 0, 0));
    Mat img2(200, 200, CV_32FC3, Scalar(0, 1, 0));
    Mat roi = img1(Rect(50, 50, 200, 200)); // roi与img1指向同一内存
    imshow("img1 before", img1);
    imshow("img2 before", img2);
    imshow("roi before", roi);
    roi = img2; // 修改roi头部，与img1无关，与img2指向同一内存
    rectangle(roi, Rect(50, 50, 100, 100), Scalar(0, 0, 1), 2);
    imshow("img1 after", img1);
    imshow("img2 after", img2);
    imshow("roi after", roi);

    waitKey();
}

  对于=，roi与img1无关，与img2指向同一内存。此时对roi画红框不会改变img1，但会相应地改变img2。

2、clone

#include <opencv2/opencv.hpp>
using namespace cv;
#include <iostream>
using namespace std;

int main()
{
    Mat img1(300, 300, CV_32FC3, Scalar(1, 0, 0));
    Mat img2(200, 200, CV_32FC3, Scalar(0, 1, 0));
    Mat roi = img1(Rect(50, 50, 200, 200)); // roi与img1指向同一内存
    imshow("img1 before", img1);
    imshow("img2 before", img2);
    imshow("roi before", roi);
    roi = img2.clone(); // roi重新分配内存并拷贝数据，roi与img1，img2无关
    rectangle(roi, Rect(50, 50, 100, 100), Scalar(0, 0, 1), 2);
    imshow("img1 after", img1);
    imshow("img2 after", img2);
    imshow("roi after", roi);

    waitKey();
}

  对于clone，clone创建一个完整副本（分配内存并拷贝数据），roi与img1，img2无关。此时对roi画红框不会改变img1和img2。

3、copyTo

#include <opencv2/opencv.hpp>
using namespace cv;
#include <iostream>
using namespace std;

int main()
{
    Mat img1(300, 300, CV_32FC3, Scalar(1, 0, 0));
    Mat img2(200, 200, CV_32FC3, Scalar(0, 1, 0));
    Mat roi = img1(Rect(50, 50, 200, 200)); // roi与img1指向同一内存
    imshow("img1 before", img1);
    imshow("img2 before", img2);
    imshow("roi before", roi);
    img2.copyTo(roi); // roi的size、type与img2一致，copyTo只拷贝数据，roi与img1指向同一内存，与img2无关
    rectangle(roi, Rect(50, 50, 100, 100), Scalar(0, 0, 1), 2);
    imshow("img1 after", img1);
    imshow("img2 after", img2);
    imshow("roi after", roi);

    waitKey();
}

  对于copyTo，若roi的size或type与img2一致，则只会拷贝数据，roi仍与img1指向同一内存，但与img2无关。此时对roi画红框会相应改变img1，而不会改变img2。

#include <opencv2/opencv.hpp>
using namespace cv;
#include <iostream>
using namespace std;

int main()
{
    Mat img1(300, 300, CV_32FC3, Scalar(1, 0, 0));
    Mat img2(200, 200, CV_32FC3, Scalar(0, 1, 0));
    Mat roi = img1(Rect(50, 50, 250, 250)); // roi与img1指向同一内存，size不一致
    imshow("img1 before", img1);
    imshow("img2 before", img2);
    imshow("roi before", roi);
    img2.copyTo(roi); // roi的size与img2不一致，copyTo重新分配内存并拷贝数据，roi与img，img2无关
    rectangle(roi, Rect(50, 50, 100, 100), Scalar(0, 0, 1), 2);
    imshow("img1 after", img1);
    imshow("img2 after", img2);
    imshow("roi after", roi);

    waitKey();
}

  对于copyTo，若roi的size或type与img2不一致，则copyTo与clone等效，copyTo重新分配内存并拷贝数据，roi与img1，img2无关。此时对roi画红框不会改变img1，img2。