円形を作成し、そこから別の円形を差し引き、それをクリップとして設定すると、必要な線に沿って何かができあがる可能性があります。クリップの粗いエッジを非表示にするには、シェイプの2px幅のストロークを描画します。
import java.awt.*;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.*;
public class OneRing {
OneRing(BufferedImage imageBG, BufferedImage imageFG) {
// presumes the images are identical in size BNI
int w = imageBG.getWidth();
int h = imageBG.getHeight();
Ellipse2D.Double ellipse1 = new Ellipse2D.Double(
w/16,h/16,7*w/8,7*h/8);
Ellipse2D.Double ellipse2 = new Ellipse2D.Double(
w/4,h/4,w/2,h/2);
Area circle = new Area(ellipse1);
circle.subtract(new Area(ellipse2));
Graphics2D g = imageBG.createGraphics();
g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g.setRenderingHint(RenderingHints.KEY_DITHERING, RenderingHints.VALUE_DITHER_ENABLE);
g.setRenderingHint(RenderingHints.KEY_FRACTIONALMETRICS, RenderingHints.VALUE_FRACTIONALMETRICS_ON);
g.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BICUBIC);
g.setClip(circle);
g.drawImage(imageFG, 0, 0, null);
g.setClip(null);
Stroke s = new BasicStroke(2);
g.setStroke(s);
g.setColor(Color.BLACK);
g.draw(circle);
g.dispose();
JLabel l = new JLabel(new ImageIcon(imageBG));
JOptionPane.showMessageDialog(null, l);
}
public static void main(String[] args) throws Exception {
URL urlFG = new URL("http://i.stack.imgur.com/OVOg3.jpg");
URL urlBG = new URL("http://i.stack.imgur.com/lxthA.jpg");
final BufferedImage biFG = ImageIO.read(urlFG);
final BufferedImage biBG = ImageIO.read(urlBG);
SwingUtilities.invokeLater(new Runnable(){
@Override
public void run() {
new OneRing(biBG, biFG);
}
});
}
}