- OpenCV - GUI
- OpenCV - Writing an Image
- OpenCV - Reading Images
- OpenCV - Storing Images
- OpenCV - Environment
- OpenCV - Overview
- OpenCV - Home
Types of Images
Image Conversion
Drawing Functions
- OpenCV - Adding Text
- OpenCV - Drawing Arrowed Lines
- OpenCV - Drawing Convex Polylines
- OpenCV - Drawing Polylines
- OpenCV - Drawing an Ellipse
- OpenCV - Drawing a Rectangle
- OpenCV - Drawing a Line
- OpenCV - Drawing a Circle
Blur
Filtering
- OpenCV - Image Pyramids
- OpenCV - Morphological Operations
- OpenCV - Erosion
- OpenCV - Dilation
- OpenCV - Filter2D
- OpenCV - SQRBox Filter
- OpenCV - Box Filter
- OpenCV - Bilateral Filter
Thresholding
Sobel Derivatives
Transformation Operations
Camera and Face Detection
Geometric Transformations
Miscellaneous Chapters
OpenCV Useful Resources
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
OpenCV - Drawing a Circle
You can draw various shapes pke Circle, Rectangle, Line, Elppse, Polypnes, Convex, Polypnes, Polypnes on an image using the respective methods of the org.opencv.imgproc package.
You can draw a circle on an image using the method circle() of the imgproc class. Following is the syntax of this method −
circle(img, center, radius, color, thickness)
This method accepts the following parameters −
mat − A Mat object representing the image on which the circle is to be drawn.
point − A Point object representing the center of the circle.
radius − A variable of the type integer representing the radius of the circle.
scalar − A Scalar object representing the color of the circle. (BGR)
thickness − An integer representing the thickness of the circle; by default, the value of thickness is 1.
Example
The following program demonstrates how to draw a circle 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.Scalar; import org.opencv.imgcodecs.Imgcodecs; import org.opencv.imgproc.Imgproc; pubpc class DrawingCircle extends Apppcation { Mat matrix = null; @Override pubpc void start(Stage stage) throws Exception { // Capturing the snapshot from the camera DrawingCircle obj = new DrawingCircle(); 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 Circle 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 a Circle Imgproc.circle ( matrix, //Matrix obj of the image new Point(230, 160), //Center of the circle 100, //Radius new Scalar(0, 0, 255), //Scalar object for color 10 //Thickness of the circle ); // 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 −
![Drawing Circle](/opencv/images/drawing_circle.jpg)