How to Select a Region of Interest on a Video like this - opencv

Question

I am working on a queue bypass detection project and i need to select a region of interest or the boundary. If a person crosses the boundary, we should get an alert. Please help me to select a region of interest in live video similar to the one in the image.
please see this image

Answer 1

After doing some research I found what you need on github
#include "opencv2/opencv.hpp"
#include <iostream>
using namespace cv;
using namespace std;
/*~~~~~~~~~~~~~~~~~~*/
char ky;
bool got_roi = false;
Point points_array[4];
Mat src, ROI_Img,backup,ROI_MASK;
Rect2d ROI_Select;
int width_roi = 0, height_roi = 0,min_x,min_y,max_x,max_y;
Rect ROI_RECT ;
vector< vector<Point> > co_ordinates;
/*~~~~~~~~~~~~~~~~~~*/
/*~~~~~~~~~~~~~~~~~~*/
//Callback for mousclick event, the x-y coordinate of mouse button-down
//are stored array of points [points_array].
void mouse_click(int event, int x, int y, int flags, void *param)
{
static int count=0;
switch (event)
{
case CV_EVENT_LBUTTONDOWN:
{
switch (count) // number of set Point
{
case 0:
cout << "Select top-right point" << endl;
break;
case 1:
cout << "Select bottom-right point" << endl;
break;
case 2:
cout << "Select bottom-left point" << endl << endl;
break;
default:
break;
}
if (!got_roi) // you are not select ROI yet!
{
points_array[count] = Point(x,y);
circle(src, points_array[count], 2, Scalar(0, 255, 0), 2); //show points on image
imshow("My_Win", src);
count++;
if (count == 4) // if select 4 point finished
{
cout << "ROI x & y points :" << endl;
cout << points_array[0] << endl;
cout << points_array[1] << endl;
cout << points_array[2] << endl;
cout << points_array[3] << endl;
cout << endl << "ROI Saved You can continue with double press any keys except 'c' " << endl <<"once press 'c' or 'C' to clear points and retry select ROI " << endl << endl;
ky = waitKey(0) & 0xFF;
if (ky == 99 || ky == 67) // c or C to clear
{
backup.copyTo(src);
points_array[0] = Point(0, 0);
points_array[1] = Point(0, 0);
points_array[2] = Point(0, 0);
points_array[3] = Point(0, 0);
imshow("My_Win", src);
count = 0;
cout << endl << endl << endl << "#--------------------- Clear Points! ------------------# " << endl << endl << endl ;
}
else // user accept points & dosn't want to clear them
{
min_x = std::min(points_array[0].x, points_array[3].x); //find rectangle for minimum ROI surround it!
max_x = std::max(points_array[1].x, points_array[2].x);
min_y = std::min(points_array[0].y, points_array[1].y);
max_y = std::max(points_array[3].y, points_array[2].y);
height_roi = max_y - min_y;
width_roi = max_x - min_x;
ROI_RECT = Rect(min_x, min_y, width_roi, height_roi);
got_roi = true;
co_ordinates.push_back(vector<Point>());
co_ordinates[0].push_back(points_array[0]);
co_ordinates[0].push_back(points_array[1]);
co_ordinates[0].push_back(points_array[2]);
co_ordinates[0].push_back(points_array[3]);
}
}
}
else { // if got_roi se true => select roi before
cout << endl << "You Select ROI Before " << endl << "if you want to clear point press 'c' or double press other keys to continue" << endl << endl;
}
break;
}
}
}
/*~~~~~~~~~~~~~~~~~~*/
int main()
{
// replace all "My_Win" with your window name
/*~~~~~~~~~~~~~~~~~~*/
namedWindow("My_Win", 1);
/*~~~~~~~~~~~~~~~~~~*/
VideoCapture input_video("Video_path");
// Set source imafe as [src]
/*~~~~~~~~~~~~~~~~~~*/
input_video >> src;
imshow("My_Win", src);
src.copyTo(backup);
setMouseCallback("My_Win", mouse_click, 0);
waitKey(0);
Mat mask(src.rows, src.cols, CV_8UC1, cv::Scalar(0));
drawContours(mask, co_ordinates, 0, Scalar(255), CV_FILLED, 8);
/*~~~~~~~~~~~~~~~~~~*/
while (1)
{
input_video >> src;
/*~~~~~~~~~~~~~~~~~~*/
//Need to copy Select ROI as MASK
src.copyTo(ROI_MASK, mask);
//Creat a rectangle around the Mask to reduce size of mask
ROI_Img = ROI_MASK(ROI_RECT);
/*~~~~~~~~~~~~~~~~~~*/
//Show Image
imshow("My_Win", ROI_Img);
// Do remaining processing here on capture roi for every frame
if(char (waitKey(1)& 0xFF) == 27) break;
}
}