Create java.awt.geom.Area from points

Question

I am trying to create a java.awt.geom.Area (or any object that uses the Shape interface) to describe a set of points that create a complex shape. Here is an example:

I am trying to create an Area object (or many Area objects) to describe the yellow area. I have an easy way of obtaining the coordinates of the yellow pixels, but I don't know how to create an Area object (or multiple Area objects) that contains all the yellow points.

This stackoverflow question seems very relevant Create closed polygon from boundary points) but is using Matlab. I think someone else asked a very similar question here (Convert a list java.awt.geom.Point2D to a java.awt.geom.Area) but the links provided in the answers are dead.

Answer 1

E.G.

import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.geom.Area;
import javax.imageio.ImageIO;
import java.io.File;
import java.net.URL;
import java.util.Date;
import javax.swing.*;

/* See also http://stackoverflow.com/q/7052422/418556 */
class ImageOutline {

    public static Area getOutline(
        BufferedImage image, Color color, boolean include, int tolerance) {

        Area area = new Area();
        for (int x=0; x<image.getWidth(); x++) {
            for (int y=0; y<image.getHeight(); y++) {
                Color pixel = new Color(image.getRGB(x,y));
                if (include) {
                    if (isIncluded(color, pixel, tolerance)) {
                        Rectangle r = new Rectangle(x,y,1,1);
                        area.add(new Area(r));
                    }
                } else {
                    if (!isIncluded(color, pixel, tolerance)) {
                        Rectangle r = new Rectangle(x,y,1,1);
                        area.add(new Area(r));
                    }
                }
            }
        }
        return area;
    }

    public static boolean isIncluded(
        Color target, Color pixel, int tolerance) {

        int rT = target.getRed();
        int gT = target.getGreen();
        int bT = target.getBlue();
        int rP = pixel.getRed();
        int gP = pixel.getGreen();
        int bP = pixel.getBlue();
        return(
            (rP-tolerance<=rT) && (rT<=rP+tolerance) &&
            (gP-tolerance<=gT) && (gT<=gP+tolerance) &&
            (bP-tolerance<=bT) && (bT<=bP+tolerance) );
    }

    public static BufferedImage drawOutline(int w, int h, Area area) {

        final BufferedImage result = new BufferedImage(
            w,
            h,
            BufferedImage.TYPE_INT_RGB);
        Graphics2D g = result.createGraphics();

        g.setColor(Color.white);
        g.fillRect(0,0,w,h);

        g.setClip(area);
        g.setColor(Color.red);
        g.fillRect(0,0,w,h);

        g.setClip(null);
        g.setStroke(new BasicStroke(1));
        g.setColor(Color.blue);
        g.draw(area);

        return result;
    }

    public static BufferedImage createAndWrite(
        BufferedImage image,
        Color color,
        boolean include,
        int tolerance,
        String name)
        throws Exception {

        int w = image.getWidth();
        int h = image.getHeight();

        System.out.println("Get Area: " + new Date() + " - " + name);
        Area area = getOutline(image, color, include, tolerance);
        System.out.println("Got Area: " + new Date() + " - " + name);

        final BufferedImage result = drawOutline(w,h,area);
        displayAndWriteImage(result, name);

        return result;
    }

    public static void displayAndWriteImage(
        BufferedImage image, String fileName) throws Exception {

        ImageIO.write(image, "png", new File(fileName));
        JOptionPane.showMessageDialog(null, new JLabel(new ImageIcon(image)));
    }

    public static void main(String[] args) throws Exception {
        URL url = new URL("https://i.stack.imgur.com/aGBuT.png");
        final BufferedImage outline = ImageIO.read(url);
        displayAndWriteImage(outline, "motorcycle-01.png");
        createAndWrite(
            outline, Color.white, false, 60, "YellowBlobOutline.png");
    }
}

Answer 2

I'd create a GeneralPath or a Path2D, both of which implement Shape. This tutorial explains how to use GeneralPath, which is very similar to Path2D. The Shape can then be used to create the Area.