How to draw a rectangle in OpenCV using C++?

To draw a rectangle, we need four points. Look at the following figure.

In the figure, there are four points x1, x2, y1 and y2. These four points are forming the four coordinates. To draw a rectangle using OpenCV, we have to define these points and show the rectangle we need a matrix. We have to declare other relevant values like the color of the line and line width.

The basic syntax of this method is as follows −


rectangle(whiteMatrix, starting, ending, line_Color, thickness);

The following program represents how to draw a rectangle in OpenCV.


using namespace cv;
using namespace std;
int main() {
   Mat whiteMatrix(200, 200, CV_8UC3, Scalar(255, 255, 255));// Declaring a white matrix//
   Point starting(40, 40);//Declaring the starting coordinate//
   Point ending(160, 100);//Declaring the ending coordinate
   Scalar line_Color(0, 0, 0);//Color of the rectangle//
   int thickness = 2;//thickens of the line//
   namedWindow("whiteMatrix");//Declaring a window to show the rectangle//
   rectangle(whiteMatrix, starting, ending, line_Color, thickness);//Drawing the rectangle//
   imshow("WhiteMatrix", whiteMatrix);//Showing the rectangle//
   waitKey(0);//Waiting for Keystroke
   return 0;


Updated on: 10-Mar-2021


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