1. 選取影象中的ROI區域：

#include<opencv2\opencv.hpp>

#include <stdio.h>  



using namespace cv;



Mat org, dst, img, tmp;



void on_mouse(int event, int x, int y, int flags, void *)

{

	static Point pre_pt = (-1, -1);

	static Point cur_pt = (-1, -1);

	if (event == CV_EVENT_LBUTTONDOWN)

	{
		pre_pt = Point(x, y);

	}

	else if (event == CV_EVENT_MOUSEMOVE && flags)//摁下左鍵，flags為1 

	{

		org.copyTo(tmp);

		cur_pt = Point(x, y);

		rectangle(tmp, pre_pt, cur_pt, Scalar(0, 255, 0, 0), 1, 8, 0);

		imshow("img", tmp);//畫的時候顯示框

	}

	else if (event == CV_EVENT_LBUTTONUP)

	{

		org.copyTo(img);

		//cur_pt = Point(x, y);

		rectangle(img, pre_pt, cur_pt, Scalar(0, 255, 0, 0), 1, 8, 0);

		imshow("img", img);//畫完後顯示框

		//img.copyTo(tmp);

		int width = abs(pre_pt.x - cur_pt.x);

		int height = abs(pre_pt.y - cur_pt.y);

		if (width == 0 || height == 0)

		{

			return;

		}

		dst = org(Rect(min(cur_pt.x, pre_pt.x), min(cur_pt.y, pre_pt.y), width, height));

		namedWindow("dst");

		imshow("dst", dst);

	}

}

void main()

{

	org = imread("123.jpg");

	org.copyTo(img);

	namedWindow("img");

	setMouseCallback("img", on_mouse, 0);

	imshow("img", img);

	waitKey(0);

}