# Draw an ellipse using OpenCV in C++

• Difficulty Level : Hard
• Last Updated : 22 Feb, 2021

In this article, the task is to draw an ellipse using OpenCV in C++. The ellipse() function from OpenCV C++ library will be used.

Syntax:

ellipse(image, centerCoordinates, axesLength, angle, startAngle, endAngle, color, thickness, lineType, shift)

Parameters:

• image: It is the image on which ellipse is to be drawn.
• centerCoordinates: Coordinates of the center of the ellipse. (Tuple of two coordinates (X-coordinate, Y-coordinate))
• axesLength:Tuple containing the major and minor axis of the ellipse (major axis length, minor axis length).
• angle: Ellipse rotation angle in degrees.
• startAngle: Starting angle of the elliptic arc(degrees).
• endAngle: Ending angle of the elliptic arc(degrees).
• color: It is the color of the borderline of the ellipse to be drawn. A tuple representing 3 colors (B, G, R) i.e., (Blue, Green, Red).
• thickness: It is the thickness of the ellipse borderline in px. The thickness of -1 px will fill the ellipse shape by the specified color.
• lineType: Type of the line. There are 3 types of line:
• LINE_4: Line was drawn using 4 connected Bresenham algorithm.
• LINE_8: Line was drawn using 8 connected Bresenham algorithm.
• LINE_AA: It draws Anti-aliased lines formed by using a Gaussian filter.
• shift: Number of fractional bits in the point coordinates.

Return Value: It returns an image.

Program 1:

Below is the C++ program demonstrating how to draw an ellipse over a self-formed background image:

## C++

 // C++ program to demonstrating ellipse // over a self-formed background image #include #include    // Drawing shapes #include    #include using namespace cv; using namespace std;    // Driver Code int main(int argc, char** argv) {     // Creating a blank image with     // white background     Mat image(500, 500, CV_8UC3,               Scalar(255, 255, 255));        // Check if the image is created     // successfully or not     if (!image.data) {         std::cout << "Could not open or "                   << "find the image\n";            return 0;     }        // Drawing the ellipse     ellipse(image, Point(256, 256),             Size(100, 50), 0, 0,             360, Scalar(0, 255, 255),             -1, LINE_AA);        // Showing image inside a window     imshow("Output", image);     waitKey(0);        return 0; }

Output:

Explanation: In the above program, an ellipse is drawn at an angle of 0 degrees i.e., horizontal ellipse.

Program 2:

Below is the C++ program illustrate rectangle over a loaded image with an ellipse around the GFG logo:

## C++

 // C++ program to demonstrate rectangle // over a loaded image with an ellipse // around the GFG logo #include #include    // Drawing shapes #include    #include using namespace cv; using namespace std;    // Driver Code int main(int argc, char** argv) {     // Reading the Image     Mat image = imread("C:/Users/harsh/Downloads/geeks.png",                        IMREAD_COLOR);        // Check if the image is created     // successfully or not     if (!image.data) {         std::cout << "Could not open or "                   << "find the image\n";         return 0;     }        // Drawing the ellipse     ellipse(image, Point(115, 110),             Size(105, 55), 0, 0,             360, Scalar(0, 255, 255),             1, LINE_AA);        // Show our image inside a window     imshow("Output", image);     waitKey(0);        return 0; }

Output:

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