How to add borders to an image using Java OpenCV library?

You can add borders to a given image using the copyMakeBorder() method, this method accepts the following parameters −

• Two Mat objects representing the source and destination images.

• An object of the class Mat representing the destination (output) image.

• Four integer variables representing the lengths of the borders in all the 4 directions of the image.

• An integer variable representing the type of the border that is to be used.

Example

import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javafx.application.Application;
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.highgui.HighGui;
import org.opencv.imgcodecs.Imgcodecs;
public class AddingBorders extends Application {
   public void start(Stage stage) throws IOException {
      //Loading the OpenCV core library
      System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
      String file ="D:\Images\cat.jpg";
      Mat src = Imgcodecs.imread(file);
      //Creating an empty matrices to store the destination image.
      Mat dst = new Mat(src.rows(), src.cols(), src.type());
      //Adding borders
      Core.copyMakeBorder(src, dst, 20, 20, 20, 20, Core.BORDER_CONSTANT);
      //Converting matrix to JavaFX writable image
      Image img = HighGui.toBufferedImage(dst);
      WritableImage writableImage= SwingFXUtils.toFXImage((BufferedImage) img, null);
      //Setting the image view
      ImageView imageView = new ImageView(writableImage);
      imageView.setX(10);
      imageView.setY(10);
      imageView.setFitWidth(575);
      imageView.setPreserveRatio(true);
      //Setting the Scene object
      Group root = new Group(imageView);
      Scene scene = new Scene(root, 595, 400);
      stage.setTitle("Adding Borders");
      stage.setScene(scene);
      stage.show();
   }
   public static void main(String args[]) {
      launch(args);
   }
}

Input Image

Output

On executing, the above program generates the following windows −