Mat img= imread（image）；Rect rect(50,20, 200, 50);Mat ROI = img(rect);imshow("ROI_WIN",ROI);

#include <opencv2/highgui/highgui.hpp>#include <opencv2/core/core.hpp>#include <opencv2/imgproc/imgproc.hpp>#include <iostream>using namespace cv;using namespace std;cv::Mat img;bool select_flag = false;cv::Rect m_select; cv::Point origin;int ROI_count;void onMouseRectPicking(int event, int x, int y, int, void*){ if (select_flag) { m_select.x = MIN(origin.x, x);//不一定要等鼠標彈起才計算矩形框，而應該在鼠標按下開始到彈起這段時間實時計算所選矩形框 m_select.y = MIN(origin.y, y); m_select.width = abs(x - origin.x);//算矩形寬度和高度 m_select.height = abs(y - origin.y); m_select &= cv::Rect(0, 0, img.cols, img.rows);//保證所選矩形框在視頻顯示區域之內 } if (event == CV_EVENT_LBUTTONDOWN) { select_flag = true;  //鼠標按下的標志賦真值 origin = cv::Point(x, y); //保存下來單擊捕捉到的點 m_select = cv::Rect(x, y, 0, 0); //這里一定要初始化，寬和高為(0,0)是因為在opencv中Rect矩形框類內的點是包含左上角那個點的，但是不含右下角那個點  } else if (event == CV_EVENT_LBUTTONUP) { select_flag = false; ROI_count++; }}int main(int argc, char* argv[] ){ img=imread("/home/drew/picture_cut/build/scenary.jpg"); bool stop = false; cv::namedWindow("capframe", CV_WINDOW_AUTOSIZE); cv::setMouseCallback("capframe", onMouseRectPicking, 0); char pic_name[40]; ROI_count=0; while(!stop) { img=imread("/home/drew/picture_cut/build/scenary.jpg"); cv::rectangle(img, m_select, cv::Scalar(255,0,0), 2, 8, 0); // 畫矩形框 cv::imshow("capframe",img); if((m_select.x!=0)&&(m_select.y!=0)&&(m_select.width!=0)&&(m_select.height!=0)) {  sprintf(pic_name,"ROI_%d.jpg",ROI_count);  Mat ROI = img(m_select);  imshow("ROI_WIN",ROI);   imwrite(pic_name,ROI);   } char key = cv::waitKey(30); if(key == 27)   stop = true;  } waitKey(0); return 0;}