How to Flip an Image Using Graphics2D in Java

Question

How can I flip an image vertically or horizontally using Graphics2D in Java?

import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;

public class ImageFlipper extends JPanel {
    private BufferedImage image;

    public ImageFlipper(BufferedImage img) {
        this.image = img;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;

        // Flip image horizontally
        g2d.scale(-1, 1);
        g2d.drawImage(image, -image.getWidth(), 0, null);

        // Alternative: Flip image vertically
        // g2d.scale(1, -1);
        // g2d.drawImage(image, 0, -image.getHeight(), null);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        BufferedImage img = ...; // Load your image here
        ImageFlipper flipper = new ImageFlipper(img);
        frame.add(flipper);
        frame.setSize(img.getWidth(), img.getHeight());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

Answer

Flipping an image in Java using the Graphics2D class involves applying a scaling transformation to the graphics context. This transformation effectively mirrors the image about a specified axis—horizontal or vertical. Below, we provide a guided approach to accomplish this using a custom JPanel.

import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;

public class ImageFlipper extends JPanel {
    private BufferedImage image;

    public ImageFlipper(BufferedImage img) {
        this.image = img;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;

        // Flip image horizontally
        g2d.scale(-1, 1);
        g2d.drawImage(image, -image.getWidth(), 0, null);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        BufferedImage img = ...; // Load your image here
        ImageFlipper flipper = new ImageFlipper(img);
        frame.add(flipper);
        frame.setSize(img.getWidth(), img.getHeight());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

Causes

The original image needs to be displayed in a flipped orientation.
Transformations such as scaling can help achieve the desired visual effect.

Solutions

Use the `scale` method of the Graphics2D class to flip the image.
Set the origin point to adjust the position of the drawn image after scaling.

Common Mistakes

Mistake: Forgetting to reset the transformation before drawing another component.

Solution: Always call `g2d.setTransform(new AffineTransform());` before drawing any other components.

Mistake: Not properly loading the image, resulting in a null reference.

Solution: Ensure that the image is loaded correctly before creating the ImageFlipper instance.

Helpers

Java image flipping
Graphics2D flip image
Java image manipulation
How to use Graphics2D
Java drawing images