How do I flip an image upside-down?

Question

I was wondering if I could find some help on this problem. I was asked to use an image ("corn.jpg"), and flip it entirely upside down. I know I need to write a program which will switch pixels from the top left corner with the bottom left, and so on, but I wasn't able to get my program to work properly before time ran out. Could anyone provide a few tips or suggestions to solve this problem? I'd like to be able to write my code out myself, so suggestions only please. Please note that my knowledge of APImage and Pixel is very limited. I am programming in Java. Here is what I managed to get done.

import images.APImage; 
import images.Pixel; 
public class Test2 
{ 
  public static void main(String [] args) 
  { 
    APImage image = new APImage("corn.jpg"); 
    int width = image.getImageWidth(); 
    int height = image.getImageHeight(); 
    int middle = height / 2; 
    //need to switch pixels in bottom half with the pixels in the top half 

    //top half of image 
    for(int y = 0; y < middle; y++) 
    { 
      for (int x = 0; x < width; x++) 
      { 
        //bottom half of image 
        for (int h = height; h > middle; h++) 
        { 
          for(int w = 0; w < width; w++) 
          { 
            Pixel bottomHalf = image.getPixel(h, w); 
            Pixel topHalf = image.getPixel(x, y); 
            //set bottom half pixels to corresponding top ones? 
            bottomHalf.setRed(topHalf.getRed()); 
            bottomHalf.setGreen(topHalf.getGreen()); 
            bottomHalf.setBlue(topHalf.getBlue()); 
            //set top half pixels to corresponding bottom ones? 
            topHalf.setRed(bottomHalf.getRed()); 
            topHalf.setGreen(bottomHalf.getGreen()); 
            topHalf.setBlue(bottomHalf.getBlue()); 
          }
        }
      }
    }
    image.draw(); 
  }
}

Thank you for your help!

Answer 1

See Transforming Shapes, Text, and Images.

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

public class FlipVertical {

    public static BufferedImage getFlippedImage(BufferedImage bi) {
        BufferedImage flipped = new BufferedImage(
                bi.getWidth(),
                bi.getHeight(),
                bi.getType());
        AffineTransform tran = AffineTransform.getTranslateInstance(0, bi.getHeight());
        AffineTransform flip = AffineTransform.getScaleInstance(1d, -1d);
        tran.concatenate(flip);

        Graphics2D g = flipped.createGraphics();
        g.setTransform(tran);
        g.drawImage(bi, 0, 0, null);
        g.dispose();

        return flipped;
    }

    FlipVertical(BufferedImage bi) {
        JPanel gui = new JPanel(new GridLayout(1,2,2,2));

        gui.add(new JLabel(new ImageIcon(bi)));
        gui.add(new JLabel(new ImageIcon(getFlippedImage(bi))));

        JOptionPane.showMessageDialog(null, gui);
    }

    public static void main(String[] args) throws AWTException {
        final Robot robot = new Robot();
        Runnable r = new Runnable() {

            @Override
            public void run() {
                final BufferedImage bi = robot.createScreenCapture(
                        new Rectangle(0, 660, 200, 100));
                new FlipVertical(bi);
            }
        };
        SwingUtilities.invokeLater(r);
    }
}