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If you don’t need a scaled instance of your BufferedImage in the memory, you can use “on-the-fly scaling”. For example, this custom JComponent can be used to display a BufferedImage and zoom it with the setScaleFactor(..)-method

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import javax.swing.JComponent;

public class ZoomableImage extends JComponent {

    private float scaleFactor;
    
    private BufferedImage originalImage;

    public ZoomableImage() {
        this.scaleFactor = 1;
        this.setSize(0, 0);
    }

    public void setImage(BufferedImage image) {
        this.originalImage = image;
        this.setSize(image.getWidth(), image.getHeight());
        //setSize does repainting, no need to call repaint()
        //this.repaint();
    }

    public void setScaleFactor(float scaleFactor) {
        this.scaleFactor = scaleFactor;
        this.repaint();
    }

    @Override
    public void paintComponent(Graphics g) {
        if (this.originalImage != null) {
            Graphics2D g2 = (Graphics2D) g;
            int newW = (int) (originalImage.getWidth() * scaleFactor);
            int newH = (int) (originalImage.getHeight() * scaleFactor);
            this.setPreferredSize(new Dimension(newW, newH));
            this.revalidate();
            g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
                    //RenderingHints.VALUE_INTERPOLATION_BILINEAR);
                    RenderingHints.VALUE_INTERPOLATION_NEAREST_NEIGHBOR);
                    //RenderingHints.VALUE_INTERPOLATION_BICUBIC);
            g2.drawImage(originalImage, 0, 0, newW, newH, null);
        }
    }
}

For some benchmarking on the different RenderingHints values see Chris Campbell’s great article The Perils of Image.getScaledInstance()

Resources:
http://java.sun.com/docs/books/tutorial/2d/advanced/quality.html
http://today.java.net/pub/a/today/2007/04/03/perils-of-image-getscaledinstance.html

In short: setSize(..) doesn’t work at all, you’ll need setPreferredSize(..) followed by revalidate()

if (changed) {
    //Update client's preferred size because
    //the area taken up by the graphics has
    //gotten larger or smaller (if cleared).
    drawingArea.setPreferredSize(/* the new size */);

    //Let the scroll pane know to update itself
    //and its scroll bars.
    drawingArea.revalidate();
}

Resources:
http://java.sun.com/docs/books/tutorial/uiswing/components/scrollpane.html#update