【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 = 0;
    while(0 == obj_selected)
    {
        obj_selected = get_rects(frame);
        if (obj_selected == 0)
        {
            cout<<"You haven't selected any rectangles. "<<endl;
        }
    }
}

void MouseSelect::select_point(Mat &frame)
{
    obj_selected = 0;
    while(0 == obj_selected)
    {
        obj_selected = get_points(frame);
        if (obj_selected == 0)
        {
            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 = 0;
    params.mode = 2;
    namedWindow(win_name,WINDOW_AUTOSIZE);
    imshow(win_name,frame);
    
    g_mousep = &params;
    setMouseCallback(win_name,on_mouse,0);
    waitKey(0);
    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 = 0;i < params.pts.size();i += 2)
    {
        pt1 = params.pts[i];
        pt2 = params.pts[i + 1];
        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 % 2)? w:w+1;
        h = (h % 2)? h:h+1;
        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 = 0;
    params.mode = 1;

    namedWindow(win_name,1);
    imshow(win_name,frame);

    g_mousep = &params;
    setMouseCallback(win_name,on_mouse,0);
    waitKey(0);

    destroyWindow(win_name);
    
    cout<<"Point Num: "<<params.pts.size()<<" Object Num: "<<params.n<<" Object Type: Point."<<endl;
    for (int i = 0;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 (1 == 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 = 3;
            circle(*g_mousep->image,cur_pt,radius,CV_RGB(255,0,0));
            imshow(g_mousep->win_name,*g_mousep->image);
            pressed = false;
            g_mousep->n++;
        }
        /* 2 == mode for selecting rectangles */
        else if (2 == 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(0,0,255));
            imshow(g_mousep->win_name,*g_mousep->image);
            pressed = false;
            g_mousep->n++;
        }
        else if (3 == g_mousep->mode)
        {
            n = g_mousep->n;

        }
    }
    else if (event == CV_EVENT_MOUSEMOVE && pressed && CV_EVENT_FLAG_LBUTTON)
    {
        if (2 == 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(0,255,0));
            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。