Re: Anti-aliasing in image clipping to non-rectangular sub-images

From:

"John B. Matthews" <nospam@nospam.invalid>

Newsgroups:

comp.lang.java.gui,comp.lang.java.programmer

Date:

Wed, 13 Aug 2008 23:18:14 -0400

Message-ID:

<nospam-A15874.23181413082008@aioe.org>

In article <48a39fd0$0$2158$ec3e2dad@news.usenetmonster.com>,
"Kenneth P. Turvey" <kt-usenet@squeakydolphin.com> wrote:

On Wed, 13 Aug 2008 19:07:14 -0700, Peter Duniho wrote:

On Wed, 13 Aug 2008 17:55:10 -0700, Kenneth P. Turvey
<kt-usenet@squeakydolphin.com> wrote:

I've got a simple problem that I'm sure someone in this group can help
me with. Let me say what I'm currently doing first.

I have an image that has some transparent portions and I want to cut a
circle out of the image.

Do you want to remove a circular area from inside the image? Or do you
want to use only a ciruclar area from inside the image as your new
image?

That is, the transformed image, will it be the original image with a
hole in it? Or will it be the original image with everything outside
the circular area excluded?

This description:

So first I trim it down to a square subimage and then I go through it
pixel by pixel and set the alpha channel to clear for those pixels
outside a circle with the sub-image's diameter.

Makes me think you're taking a circular subset of the image, but other
parts of your message seem to contradict that. I'm a bit confused.

If I have understood the goal correctly, then it seems to me that the
easiest way to transform your original image is to draw it into a new
image, clipping to the circular shape you want.

For example, here's some code that works when just drawing into the
Graphics2D passed to the paintComponent() method:

     // Where x, y, width, and height describe your circular area and
     image
is a reference
     // to the image you want to clip

     Area areaOval = new Area(new Arc2D.Double(x, y, width, height, 0,
     360,
Arc2D.PIE));
     Shape shapeClipSave = gfx2.getClip();

     gfx2.setClip(areaOval);
     gfx2.drawImage(image, 0, 0, null);
     gfx2.setClip(shapeClipSave);

You should be able to use basically the same thing drawing into a
Graphics2D instance you get from a new BufferedImage instance. Just
make sure you've enabled anti-aliased rendering, and when the image is
drawn clipped into the new BufferedImage, the edges should wind up
anti-aliased.

Pete

I tried what you suggested, but with disappointing results. Here's the
altered method:

   private void clearOutsideCircle() {
        assert image.getWidth() == image.getHeight() : "Image should be
square";
        int radius = image.getWidth() / 2;
        Area areaOval = new Area(new Arc2D.Double(0, 0, image.getWidth(),
                image.getHeight(), 0, 360, Arc2D.PIE));
        BufferedImage newImage = new BufferedImage(image.getWidth(),
                image.getHeight(), BufferedImage.TYPE_4BYTE_ABGR);
        Graphics2D graphics = newImage.createGraphics();
        graphics.setRenderingHint(RenderingHints.KEY_ALPHA_INTERPOLATION,
                RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY);
        graphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);
        graphics.setClip(areaOval);
        graphics.drawImage(image, 0, 0, null);
        image = newImage;
    }

After this the image still doesn't look anti-aliased. It seems like the
clipping region is either on or off.

Do you see anything in the code that might be the problem? Any other
suggestions?

Some implementations do better than others at honoring the hints. Try
this with any .jpg:

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

public class Clip extends JPanel {

    private BufferedImage image;
    private Ellipse2D.Double border = new Ellipse2D.Double();

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

    public Clip() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(this);
        try {
            image = ImageIO.read(new File("clip.jpg"));
        } catch (IOException ioe) {
            System.err.println(ioe);
            System.exit(1);
        }
        frame.setSize(new Dimension(
            image.getWidth(), image.getHeight()));
        frame.setVisible(true);
    }

    public void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);

        int width = getWidth();
        int height = getHeight();
        g2d.setPaint(Color.BLUE);
        g2d.fillRect(0, 0, width, height);
        border.setFrame(0, 0, width, height);
        g2d.setClip(border);
        g2d.drawImage(image, 0, 0, width, height, this);
    }
}
--
John B. Matthews
trashgod at gmail dot com
home dot woh dot rr dot com slash jbmatthews