【OpenCV】选择ROI区域

问题描述：在测试目标跟踪算法时，需要选择不同区域作为目标，进行目标跟踪，测试目标跟踪的效果。

解决思路：

1.OpenCV中提供了鼠标交互控制，利用setMouseCallback()给固定的窗口设置鼠标回调函数。

2.在鼠标回调函数中，选择感兴趣区域。

代码实现如下，将感兴趣区域封装在MouseSelect类中，提供选择点和矩形框两种模式。

 #pragma once
 #ifndef __MOUSESELECT_H__
 #define __MOUSESELECT_H__
 
 #include <opencv2/opencv.hpp>
 #include <iostream>
 
 #define MAX_OBJECTS    10
 using namespace cv;
 using namespace std;
 typedef struct MouseSelectParams
 {
     vector<Point> pts;        //Points of selected
     char        *win_name;
     Mat            *image;
     unsigned int mode;        //1 Point,2 Rect
     int             n;            // selected object number
 }MouseSelectParams;
 
 void on_mouse(int event,int x,int y,int flags,void *param);
 class MouseSelect
 {
 public:
     MouseSelect();
     ~MouseSelect();
 
     void select_rect(Mat &frame);
     void select_point(Mat &frame);
 
     vector<Point> vPoints;
     vector<Rect> vRects;
     unsigned int obj_selected;
 private:
     int get_rects(Mat &frame);
     int get_points(Mat &frame);
 
 };
 #endif

 #include "MouseSelect.h"
 
 MouseSelectParams *g_mousep;
 MouseSelect::MouseSelect() {}
 
 MouseSelect::~MouseSelect() {}
 
 void MouseSelect::select_rect(Mat &frame)
 {
     obj_selected = ;
     while( == obj_selected)
     {
         obj_selected = get_rects(frame);
         if (obj_selected == )
         {
             cout<<"You haven't selected any rectangles. "<<endl;
         }
     }
 }
 
 void MouseSelect::select_point(Mat &frame)
 {
     obj_selected = ;
     while( == obj_selected)
     {
         obj_selected = get_points(frame);
         if (obj_selected == )
         {
             cout<<"You haven't selected any points."<<endl;
         }
     }
 }
 
 int MouseSelect::get_rects(Mat &frame)
 {
     char *win_name = "Init Frame";
     MouseSelectParams params;
     params.win_name = win_name;
     params.image = &frame;
     params.n = ;
     params.mode = ;
     namedWindow(win_name,WINDOW_AUTOSIZE);
     imshow(win_name,frame);
 
     g_mousep = &params;
     setMouseCallback(win_name,on_mouse,);
     waitKey();
     destroyWindow(win_name);
 
     int x1,x2,y1,y2,w,h;
     Rect rt;
     Point pt1,pt2;
     cout<<"Point Num: "<<params.pts.size()<<" Object Num: "<<params.n<<" Object Type: Rect."<<endl;
     for(int i = ;i < params.pts.size();i += )
     {
         pt1 = params.pts[i];
         pt2 = params.pts[i + ];
         x1 = min(pt1.x,pt2.x);
         x2 = max(pt1.x,pt2.x);
         y1 = min(pt1.y,pt2.y);
         y2 = max(pt1.y,pt2.y);
         w = x2 - x1;
         h = y2 - y1;
         w = (w % )? w:w+;
         h = (h % )? h:h+;
         rt.x = x1;
         rt.y = y1;
         rt.width = w;
         rt.height = h;
         vRects.push_back(rt);
     }
     return params.n;
 }
 
 int MouseSelect::get_points(Mat &frame)
 {
     char    *win_name = "Init Frame";
     MouseSelectParams params;
     params.win_name = win_name;
     params.image = &frame;
     params.n = ;
     params.mode = ;
 
     namedWindow(win_name,);
     imshow(win_name,frame);
 
     g_mousep = &params;
     setMouseCallback(win_name,on_mouse,);
     waitKey();
 
     destroyWindow(win_name);
 
     cout<<"Point Num: "<<params.pts.size()<<" Object Num: "<<params.n<<" Object Type: Point."<<endl;
     for (int i = ;i < params.n;i++)
     {
         vPoints.push_back(params.pts[i]);
     }
     return params.n;
 }
 
 void on_mouse(int event,int x,int y,int flags,void *param)
 {
     int        n;
     static bool pressed = false;
     static Point cur_pt;
     static Point prev_pt;
     /* on left button press, remember first corner of rectangle around object */
     if (event == CV_EVENT_LBUTTONDOWN)
     {
         n = g_mousep->n;
         if (n == MAX_OBJECTS)
         {
             return;
         }
         prev_pt.x = x;
         prev_pt.y = y;
         //cout<<prev_pt.x <<","<<prev_pt.y<<" "<<cur_pt.x<<","<<cur_pt.y<<endl;
         pressed = true;
     }
     /* on left button up, finalise the rectangle and draw it in black */
     else if(event == CV_EVENT_LBUTTONUP && pressed)
     {
         /* 1 == mode for selecting points */
         if ( == g_mousep->mode)
         {
             n = g_mousep->n;
             if (n == MAX_OBJECTS)
             {
                 return;
             }
             cur_pt.x = x;
             cur_pt.y = y;
             g_mousep->pts.push_back(cur_pt);
             int radius = ;
             circle(*g_mousep->image,cur_pt,radius,CV_RGB(,,));
             imshow(g_mousep->win_name,*g_mousep->image);
             pressed = false;
             g_mousep->n++;
         }
         /* 2 == mode for selecting rectangles */
         else if ( == g_mousep->mode)
         {
             n = g_mousep->n;
             if (n == MAX_OBJECTS)
             {
                 return;
             }
             cur_pt.x = x;
             cur_pt.y = y;
             g_mousep->pts.push_back(prev_pt);
             g_mousep->pts.push_back(cur_pt);
         //    cout<<prev_pt.x <<","<<prev_pt.y<<" "<<cur_pt.x<<","<<cur_pt.y<<endl;
             rectangle(*g_mousep->image,prev_pt,cur_pt,CV_RGB(,,));
             imshow(g_mousep->win_name,*g_mousep->image);
             pressed = false;
             g_mousep->n++;
         }
         else if ( == g_mousep->mode)
         {
             n = g_mousep->n;
 
         }
     }
     else if (event == CV_EVENT_MOUSEMOVE && pressed && CV_EVENT_FLAG_LBUTTON)
     {
         if ( == g_mousep->mode)
         {
             n = g_mousep->n;
             if (n == MAX_OBJECTS)
             {
                 return;
             }
             cur_pt.x = x;
             cur_pt.y = y;
             Mat tmp = (*g_mousep->image).clone();
             //cout<<prev_pt.x <<","<<prev_pt.y<<" "<<cur_pt.x<<","<<cur_pt.y<<endl;
             rectangle(tmp,prev_pt,cur_pt,CV_RGB(,,));
             imshow(g_mousep->win_name,tmp);
         }
     }
 }

代码分析：

on_mouse()回调函数，对应于一个显示窗口。

在回调函数处理鼠标事件，要理解一个鼠标点击过程，会产生多个事件。

例如：鼠标左击，对应着CV_EVENT_LBUTTONDOWN和CV_EVENT_LBUTTONUP。

在选择矩形框区域时，CV_EVENT_LBUTTONDOWN记录一个对角点；CV_EVENT_MOUSEMOVE记录选对矩形框的中间过程，并显示出来，便于用户调整选择的区域；CV_EVENT_LBUTTONUP记录另一个对角点，CV_EVENT_LBUTTONUP响应后，完成一个矩形框的选择。

在选择点时，只需记录CV_EVENT_LBUTTONUP事件响应的坐标。