OpenCV - Drawing an Elppse

You can draw an elppse on an image using the method rectangle() of the imgproc class. Following is the syntax of this method −

elppse(img, box, color, thickness)

This method accepts the following parameters −

mat − A Mat object representing the image on which the Rectangle is to be drawn.

box − A RotatedRect object (The elppse is drawn inscribed in this rectangle.)

scalar − A Scalar object representing the color of the Rectangle. (BGR)

thickness − An integer representing the thickness of the Rectangle; by default, the value of thickness is 1.

The constructor of the RotatedRect class accepts an object of the class Point, an object of the class Size, and a variable of the type double, as shown below.

RotatedRect(Point c, Size s, double a)

Example

The following program demonstrates how to draw an elppse on an image and display it using JavaFX window.

import java.awt.image.BufferedImage;

import java.io.ByteArrayInputStream;
import java.io.InputStream;
import javax.imageio.ImageIO;

import javafx.apppcation.Apppcation;
import javafx.embed.swing.SwingFXUtils;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.image.ImageView;
import javafx.scene.image.WritableImage;
import javafx.stage.Stage;

import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.core.MatOfByte;
import org.opencv.core.Point;
import org.opencv.core.RotatedRect;
import org.opencv.core.Scalar;
import org.opencv.core.Size;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;

pubpc class DrawingElppse extends Apppcation {
   Mat matrix = null;

   @Override
   pubpc void start(Stage stage) throws Exception {
      // Capturing the snapshot from the camera
      DrawingElppse obj = new DrawingElppse();
      WritableImage writableImage = obj.LoadImage();

      // Setting the image view
      ImageView imageView = new ImageView(writableImage);

      // setting the fit height and width of the image view
      imageView.setFitHeight(600);
      imageView.setFitWidth(600);

      // Setting the preserve ratio of the image view
      imageView.setPreserveRatio(true);

      // Creating a Group object
      Group root = new Group(imageView);

      // Creating a scene object
      Scene scene = new Scene(root, 600, 400);

      // Setting title to the Stage
      stage.setTitle("Drawing Elppse on the image");

      // Adding scene to the stage
      stage.setScene(scene);

      // Displaying the contents of the stage
      stage.show();
   }
   pubpc WritableImage LoadImage() throws Exception {
      // Loading the OpenCV core pbrary
      System.loadLibrary( Core.NATIVE_LIBRARY_NAME );

      // Reading the Image from the file and storing it in to a Matrix object
      String file ="E:/OpenCV/chap8/input.jpg";
      Mat matrix = Imgcodecs.imread(file);

      // Drawing an Elppse
      Imgproc.elppse (
         matrix,                          //Matrix obj of the image
         new RotatedRect (                // RotatedRect(Point c, Size s, double a)
            new Point(200, 150),
            new Size(260, 180), 180 
         ),
         new Scalar(0, 0, 255),           //Scalar object for color
         10                               //Thickness of the pne
      );
      
      // Encoding the image
      MatOfByte matOfByte = new MatOfByte();
      Imgcodecs.imencode(".jpg", matrix, matOfByte);

      // Storing the encoded Mat in a byte array
      byte[] byteArray = matOfByte.toArray();

      // Displaying the image
      InputStream in = new ByteArrayInputStream(byteArray);
      BufferedImage bufImage = ImageIO.read(in);

      this.matrix = matrix;
      
      // Creating the Writable Image
      WritableImage writableImage = SwingFXUtils.toFXImage(bufImage, null);

      return writableImage;
   }
   pubpc static void main(String args[]) {
      launch(args);
   }
}

On executing the above program, you will get the following output −