How do I set the opacity of a JLabel/JLabel's Image?

[Dan Kao]

I'm trying to make a JLabel with an image fade in from transparent to fully visible.
Is this possible with the JLabel itself or would I have to change the Image?
If I'd have to change the Image's opacity how would I do this?

Thanks

[Rob Camick]

Here is some old code I found on the web that shows one way to do this:

import java.awt.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.io.*;
import java.net.*;
import javax.imageio.*;
import javax.swing.*;
import javax.swing.event.*;

public class TransparentImage extends JPanel
{
	private BufferedImage backImage, frontImage;
	private float alpha = 1;

	public TransparentImage()
	{
		try
		{
			backImage = ImageIO.read(new File("mong.jpg") );
			frontImage = ImageIO.read(new File("dukeWaveRed.gif") );
		}
		catch(Exception e)
		{
			System.out.println(e);
		}
	}

	@Override
	public Dimension getPreferredSize()
	{
		return new Dimension(backImage.getWidth(), backImage.getHeight());
	}

	public void setAlpha(float alpha)
	{
		this.alpha = alpha;
		repaint();
	}

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

		//  Paint background image

		Graphics2D g2 = (Graphics2D) g;
		int x = (getWidth() - backImage.getWidth())/2;
		int y = (getHeight()- backImage.getHeight())/2;
		g2.drawRenderedImage(backImage, AffineTransform.getTranslateInstance(x, y));

		//  Paint foreground image with appropriate alpha value

		Composite old = g2.getComposite();
		g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha));
		x = (getWidth() - frontImage.getWidth())/2;
		y = (getHeight()- frontImage.getHeight())/2;
		g2.drawRenderedImage(frontImage, AffineTransform.getTranslateInstance(x, y));
		g2.setComposite(old);
	}

	private static void createAndShowUI()
	{
		final TransparentImage app = new TransparentImage();

		JSlider slider = new JSlider();
		slider.addChangeListener(new ChangeListener()
		{
			public void stateChanged(ChangeEvent e)
			{
				JSlider source = (JSlider) e.getSource();
				app.setAlpha(source.getValue()/100f);
			}
		});
		slider.setValue(100);

		JFrame frame = new JFrame("Transparent Image");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.add( app );
		frame.add(slider, BorderLayout.SOUTH);
		frame.setLocationByPlatform( true );
		frame.pack();
		frame.setVisible( true );
	}

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

Use the slider to change the opacity of the foreground image.

[Dan Kao]

Thanks, works well.
Sorry to bother, but how would I make a loop to increase the value of alpha from 0 to 1 manually without a slider?

[Rob Camick]

Use a Swing Timer.

[Dan Kao]

Thanks, did that