Scaling an image quickly, and making sure it actually scales

Question

I am trying to scale a screenshot taken by:

robot.createScreenCapture(SCREEN_RECT);

Im trying to get it down to an image that is 600X400 and fits into a JFrame that is 600X400 My program is using a swing worker to create an video out of each picture, or frames. The frames have a delay of 200ms per each. the image when told to rescale just shows the original image at the original dimensions. Does anyone know how to fix this, or should I just give up on the resize-ing?

@SuppressWarnings("serial")
public class temporaryShit extends JPanel 
{
    private static final int width = 600;
    private static final int height = 400;
    private JLabel displayedLabel = new JLabel();

    public temporaryShit() 
    {
        setLayout(new BorderLayout());
        add(displayedLabel);
        try {
            MySwingWorker mySwingWorker = new MySwingWorker();
            mySwingWorker.execute();
        } catch (AWTException e) {
        }
    }

    public void setLabelIcon(Icon icon) {
        displayedLabel.setIcon(icon);
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(width, height);
    }

    private class MySwingWorker extends SwingWorker<Void, Icon> 
    {
        private final Rectangle SCREEN_RECT = new Rectangle(0, 0, width, height);
        private long delay = 200;
        private Robot robot = null;

        public MySwingWorker() throws AWTException 
        {
            robot = new Robot();
        }

        @Override
        protected Void doInBackground() throws Exception 
        {
            Timer utilTimer = new Timer();
            TimerTask task = new TimerTask() 
            {
                @Override
                public void run() 
                {
                    BufferedImage capturedImage = captureScreen();
                    publish(new ImageIcon(capturedImage));
                }
            };
            utilTimer.scheduleAtFixedRate(task, delay, delay);
            return null;
        }

        @Override
        protected void process(List<Icon> chunks) 
        {
            for (Icon icon : chunks) 
            {
                setLabelIcon(icon);
            }
        }

        private BufferedImage captureScreen() 
        {
            BufferedImage img = robot.createScreenCapture(SCREEN_RECT);
            return createResizedImage(img, width, height);
        }

        public BufferedImage createResizedImage(Image original, int width, int height) 
        {
            BufferedImage scaledBI = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
            Graphics2D g = scaledBI.createGraphics();
            g.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
            g.drawImage(original, 0, 0, width, height, null);
            g.dispose();
            return scaledBI;
        }
    }

    private static void createAndShowGui() 
    {
        temporaryShit mainPanel = new temporaryShit();

        JFrame frame = new JFrame("SwingWorker Eg");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) 
    {
        SwingUtilities.invokeLater(new Runnable() 
        {
            public void run() 
            {
                createAndShowGui();
            }
        });
    }
}

Answer 1

You already have a new image with specified size - scaled, which you can use for rendering.

Here is a simple example:

import java.awt.Image;
import java.awt.image.BufferedImage;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.*;

class TestBrightness {
    public static void main(String args[]) {
        try {
            URL imageUrl = new URL(
                    "http://duke.kenai.com/comfyChair/ComfyChairRadSmall.jpg");

            BufferedImage ioImage = ImageIO.read(imageUrl);

            JPanel panel = new JPanel();
            Image scaledImg = ioImage.getScaledInstance(ioImage.getWidth() / 2, 
                    ioImage.getHeight() / 2, Image.SCALE_SMOOTH);

            panel.add(new JLabel(new ImageIcon(ioImage)));
            panel.add(new JLabel(new ImageIcon(scaledImg)));

            JOptionPane.showMessageDialog(null, panel, "100% vs 50%",
                    JOptionPane.INFORMATION_MESSAGE);

        } catch (Exception e) {
            JOptionPane.showMessageDialog(null, e.getMessage(), "Failure",
                    JOptionPane.ERROR_MESSAGE);
            e.printStackTrace();
        }
    }
}

As a side note, there are many ways to scale an image and Image.getScaledInstance() may not be the best. You may be interested to take a look at The Perils of Image.getScaledInstance() for some details on Image.getScaledInstance()

EDIT: question update

Last question update removed all the details regarding getScaledInstance and invalidated this answer. getScaledInstance is a very slow method and it is also asynchronous. Try this method to get a resized image:

public static BufferedImage createResizedImage(Image original, int width,
        int height) {
    BufferedImage scaledBI = new BufferedImage(width, height,
            BufferedImage.TYPE_INT_ARGB);
    Graphics2D g = scaledBI.createGraphics();
    g.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
            RenderingHints.VALUE_INTERPOLATION_BILINEAR);
    g.drawImage(original, 0, 0, width, height, null);
    g.dispose();
    return scaledBI;
}

You may want to change rendering hints for better quality.

For a nicer and more complete image scaler take a look at getFasterScaledInstance() from Filthy Rich Clients book.

EDIT : last question update with posted code and SwingWorker

The implementation of SwingWorker is not correct. doInBackground() schedules java.Utils.Timer. This timer handles all updates, while the actual SwingWorker worker thread ends. All updates from the timer are fired not on Event Dispatch Thread. It may not be safe to allocate ImageIcon not on EDT. And for sure it is not safe to update UI, ie calling setLabelIcon() not on EDT. See Concurrency in Swing tutorial for details.

You can add while loop and Thread.sleep in doInBackground() and remove the timer. Alternatively, Swing timer may be more suitable for this case. Here is an example:

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

public class DemoRobotPanel extends JPanel{
    private static final long serialVersionUID = 1L;

    private Image image;
    private Robot robot;
    private Rectangle CAPTURE_RECT;
    private int TIMER_DELAY = 1000;
    private int desiredWidth = 600;
    private int desiredHeight = 400;

    public DemoRobotPanel() {
        CAPTURE_RECT = new Rectangle(Toolkit.getDefaultToolkit().getScreenSize());

        try {
            robot = new Robot();

            ActionListener taskPerformer = new ActionListener() {
                public void actionPerformed(ActionEvent evt) {
                    try {
                        BufferedImage img = robot.createScreenCapture(CAPTURE_RECT);
                        setImage(img);
                    } catch (HeadlessException e) {
                        e.printStackTrace();
                    }
                }
            };

            Timer timer = new Timer(TIMER_DELAY, taskPerformer);
            timer.start();

        } catch (AWTException ex) {
            // TODO Auto-generated catch block
            ex.printStackTrace();
        }
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(desiredWidth, desiredHeight);
    }

    public void setImage(Image image) {
        this.image = image;
        repaint();
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (image != null)
            g.drawImage(image, 0, 0, getWidth(), getHeight(), this);
    }

    private static void createAndShowGui()  {
        final DemoRobotPanel panel = new DemoRobotPanel();
        JFrame frame = new JFrame("Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(panel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGui();
            }
        });
    }
}