signed-distance-field-generator/src/Main.java

import javax.imageio.ImageIO;
import java.io.File;
import java.awt.image.BufferedImage;

public class Main {
    private static int radius = 0;
    private static BufferedImage source = null;
    private static BufferedImage destination = null;

    public static void main(String[] args) {
        if(args.length < 3) {
            System.out.println("... <src> <dest> <radius>");
            return;
        }
        try {
            radius = Integer.parseInt(args[2]) + 1;
        } catch(NumberFormatException ex) {
            System.out.printf("'%s' is an invalid radius\n", args[2]);
            return;
        }
        try {
            source = ImageIO.read(new File(args[0]));
        } catch(Exception ex) {
            System.out.printf("cannot read source '%s'\n", args[0]);
            return;
        }
        int width = source.getWidth();
        int height = source.getHeight();
        destination = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);

        for(int x = 0; x < width; x++) {
            for(int y = 0; y < height; y++) {
                int minX = Math.max(x - radius, 0);
                int maxX = Math.min(x + radius, width - 1);
                int minY = Math.max(y - radius, 0);
                int maxY = Math.min(y + radius, height - 1);

                int distance = radius;
                for(int ix = minX; ix <= maxX; ix++) {
                    for(int iy = minY; iy <= maxY; iy++) {
                        int c = source.getRGB(ix, iy);
                        int sum = (c & 0xFF) + ((c >> 8) & 0xFF) + ((c >> 16) & 0xFF);
                        if(sum < 383) {
                            double d = Math.hypot(x - ix, y - iy);
                            if(d > radius) {
                                d = radius;
                            }
                            distance = Math.min(distance, (int) d);
                        }
                    }
                }
                int intensity = 180 * distance / radius + 75;
                intensity &= 0xFF;
                int c = intensity | (intensity << 8) | (intensity << 16) | 0xFF000000;
                destination.setRGB(x, y, c);
            }
        }

        try {
            ImageIO.write(destination, "png", new File(args[1]));
        } catch(Exception ex) {
            System.out.printf("cannot write destination '%s'\n", args[0]);
        }
    }
}