Please help me merge two images

Question

I've been reading tutorials for hours, and trying everything I can think of, but I just can't figure this out.
I have two BufferedImages (TYPE_INT_RGB), and I want to be able to create an alpha channel "mask" that lets me punch "holes" (antialiased) in the top one to have the bottom one show through. I can draw white circles (Ellipse2D.Double) to my heart's content on the top or bottom image, but I can't figure out how to use this as a alpha channel mask or how to use AlphaComposite to put it all together. Can someone please offer help?

Answer 1

I merged the top 2 responses together to get an antialiased version. Then I saw the post below. Can anyone comment on which version is more efficient? Thanks for all your help.
import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GraphicsConfiguration;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.Rectangle;
import java.awt.RenderingHints;
import java.awt.Transparency;
import java.awt.geom.Area;
import java.awt.geom.Ellipse2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
public class ImageHoles extends JPanel {
    BufferedImage[] images;
    Area mask;
    ImageHoles(BufferedImage[] images) {
        this.images = images;
        // Set the mask = null and call repaint
        // inside componentResized method of a
        // ComponentListener added to this.
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        int w = getWidth();
        int h = getHeight();
        int x = (w - images[0].getWidth())/2;
        int y = (h - images[0].getHeight())/2;
        // draw bottom image
        g.drawImage(images[0], x, y, this);
        x = (w - images[1].getWidth())/2;
        y = (h - images[1].getHeight())/2;
        if(mask == null) {
            createMask(x, y);
        // from Chris Campbell's Blog (see above)
//      Create a translucent intermediate image in which we can perform
//      the soft clipping
        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
        GraphicsDevice gs = ge.getDefaultScreenDevice();
        GraphicsConfiguration gc = gs.getDefaultConfiguration();
        BufferedImage img = gc.createCompatibleImage(w, h, Transparency.TRANSLUCENT);
        Graphics2D g2 = img.createGraphics();
//      Clear the image so all pixels have zero alpha
        g2.setComposite(AlphaComposite.Clear);
        g2.fillRect(0, 0, w, h);
        g2.setComposite(AlphaComposite.Src);
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setClip(mask);
        g2.setColor(Color.WHITE);
        g2.fill(mask);
        BufferedImage hi = images[1];
        g2.setComposite(AlphaComposite.SrcAtop);
        g2.drawImage(hi, 0,0,hi.getWidth(), hi.getHeight(), this);
        g2.dispose();
        // from Chris Campbell's Blog (see above)
        // draw masked antialias layer
        g.drawImage(img, x, y, this);
    private void createMask(int x, int y) {
        int w = images[1].getWidth();
        int h = images[1].getHeight();
        Rectangle r = new Rectangle(x, y, w, h);
        Ellipse2D e1 = new Ellipse2D.Double(x+20, y+75, 25, 25);
        int cx = x + w/2;
        int cy = y + h/2;
        Ellipse2D e2 = new Ellipse2D.Double(cx-30, cy-30, 60, 60);
        Ellipse2D e3 = new Ellipse2D.Double(x+w-60, y+h-60, 40, 40);
        mask = new Area(r);
        mask.subtract(new Area(e1));
        mask.subtract(new Area(e2));
        mask.subtract(new Area(e3));
    public static void main(String[] args) throws IOException {
        String[] ids = { "polarBear", "hawk" };
        BufferedImage[] images = new BufferedImage[ids.length];
        for(int j = 0; j < images.length; j++) {
            String path = "images/" + ids[j] + ".jpg";
            images[j] = ImageIO.read(new File(path));
        ImageHoles test = new ImageHoles(images);
        test.setPreferredSize(new Dimension(images[0].getWidth(),images[0].getHeight()));
        JOptionPane.showMessageDialog(null, test, "", -1);
}