why is my image in Java application messed when it is scaled wider? (including code to show the problem)

Question

Somehow the image is messed up when it is scaled to be relatively wider. It only happens on some machine; everything seems fine on a different machine. And it only happens for some images.

Here is the messed up display:

This is when I make the window (JFrame) a little wide, so it becomes OK:

(Note I only showed the top part of image, so the grass in the messed-up version is not in the second one)

The complete code to demonstrate this:

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;

import javax.imageio.ImageIO;
import javax.swing.JComponent;
import javax.swing.JFrame;


public class Imager {

 /**
  * @param args
  */
 public static void main(String[] args) {
  JFrame frame = new JFrame();
  ImageComponent component = new ImageComponent("P1010013.JPG");
  frame.add(component);
  frame.setPreferredSize(new Dimension(300, 300));
  frame.pack();
  frame.setVisible(true);
 }

 static class ImageComponent extends JComponent {
  Image img;
  ImageComponent(String file) {
   InputStream inputStream;
   try {
    inputStream = new FileInputStream(file);
    img = ImageIO.read(inputStream);
   } catch (FileNotFoundException e) {
    e.printStackTrace();
   } catch (IOException e) {
    e.printStackTrace();
   }
  }

  protected void paintComponent(Graphics g) {
   super.paintComponent(g);
   // g.drawImage(img, 0, 0, 100, 100, null);
   g.drawImage(img, 0, 0, 1000, 1000, null);
  }

 }

}

Answer 1

You need to construct your GUI on the event dispatch thread (EDT).

Addendum 1: Here's a complete example.

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Imager {

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new ImagePanel("P1010013.JPG"));
                frame.pack();
                frame.setVisible(true);
            }
        });
    }

    private static class ImagePanel extends JPanel {

        BufferedImage img;

        ImagePanel(String name) {
            super(true);
            try {
                img = ImageIO.read(new File(name));
                this.setPreferredSize(new Dimension(
                    img.getWidth(), img.getHeight()));
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        @Override
        protected void paintComponent(Graphics g) {
            g.drawImage(img, 0, 0, this.getWidth(), this.getHeight(), null);
        }
    }
}

Also, Ash is right about scaling. Try g.drawImage(img, 0, 0, null); instead.

Addendum 2: You can determine if you're drawing on the EDT using isEventDispatchThread().

Addendum 3: I've expanded the example above.

Addendum 4: As Ash notes, "If you do not honor the opaque property you will likely see visual artifacts."—JComponent.

Answer 2

(Moved from comments): Extending a JComponent could be part of the problem. Since a JComponent is non-opaque by default, the background won't be cleared as part of the repaint process. Using a JPanel (opaque by default, but otherwise fairly similar to a JComponent) could fix the problem.