#1. Crop an Image

//including libraries
#include
#include
#include
using namespace std;
using namespace cv;

Mat img;

//Advice:Refer 'main()' function first.

//create boolean variables
bool lup=false, ldown=false;

//opencv allows to create 'Point' variables, which stores the x,y coordinates
//think of the point as an Object and coordinates as its Property.
Point corner1, corner2;
Rect box;

//self-explanatory
static void mouse_callback(int event, int x,int y, int, void *){
 if(event==EVENT_LBUTTONDOWN){
  ldown=true;
  corner1.x=x;
  corner1.y=y;
 }
 if(event==EVENT_LBUTTONUP){
  lup=true;
  corner2.x=x;
  corner2.y=y;
 }
 if(ldown==true && lup==false){
  Point pt;
  pt.x=x;
  pt.y=y;
//clone the original image
  Mat local_img=img.clone();
  rectangle(local_img, corner1,pt, Scalar(0,0,255));
  imshow("Image",local_img);
 }

 if(ldown==true && lup==true){
  box.width = abs(corner1.x - corner2.x);
  box.height = abs(corner1.y - corner2.y);
  box.x = min(corner1.x, corner2.x);
  box.y = min(corner1.y, corner2.y);
  
//the 'crop' function crops the image 'img' in the dimensions of 'box'
                Mat crop(img,box);
  namedWindow("Crop");
  imshow("Crop",crop);
  ldown=false;
  lup=false;
 }
}

int main()
{
       //read an image in Mat variable 'img'
 img=imread("images/image.jpg");
 namedWindow("Image");
 imshow("Image",img);

       //setMouseCallback is a function which, in simple language, records the mouse events, namely,
          // clicks and position of clicks.
 setMouseCallback("Image",mouse_callback);

 while(char(waitKey(0))!='q'){ }
 return 0;
}