ImageCombiner.java

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

public class ImageCombiner {

    public static void main(String[] args) throws IOException {
        if(args.length < 2){
            System.out.println("Usage: java -jar <jar> src out -s");
        }
        boolean flip = args.length == 3 && args[2].equals("-s");
        BufferedImage im = ImageIO.read(new File(args[0]));
        if(im.getWidth()!=im.getHeight())
            throw new IllegalArgumentException("Image must be quadratic");
        BufferedImage res = new BufferedImage(im.getWidth(), im.getHeight(), BufferedImage.TYPE_INT_ARGB);
        for(int y = 0; y < res.getWidth(); y++){
            double yd = (y+0.5)/res.getWidth();
            for(int x = 0; x < res.getHeight(); x++){
                Color c=null;
                double xd = (x+0.5)/res.getHeight();
                if(xd <= 1-yd){
                    double t2l = xd/(xd+yd) - 0.5;
                    c=colorAverage(4*t2l*t2l*t2l+0.5, im.getRGB(x,y), im.getRGB(flip?im.getWidth()-y:y,x));//im.getRGB(flip?im.getWidth()-y:y,x));
                }else{
                    double r2b = (1-xd)/(2-xd-yd) - 0.5;
                    c=colorAverage(4*r2b*r2b*r2b+0.5, im.getRGB(x,y), im.getRGB(flip?im.getWidth()-y:y,x));//im.getRGB(x,y));
                }

                res.setRGB(x,y,c.getRGB());
            }
        }
        File of = new File(args[1]);
        String[] ss = of.getName().split(".");
        String s = ss.length != 0 ? ss[ss.length-1].toLowerCase():"png";
        ImageIO.write(res, s, of);
        System.out.println("Wrote "+s+" to "+of.getAbsolutePath());
    }

    public static Color colorAverage(double mix, int rgb1, int rgb2){
        Color c1 = new Color(rgb1), c2 = new Color(rgb2);
        double l = mix, r=1-mix;
        return new Color((int)Math.sqrt(l*c1.getRed()*c1.getRed()+r*c2.getRed()*c2.getRed()),
                (int)Math.sqrt(l*c1.getGreen()*c1.getGreen()+r*c2.getGreen()*c2.getGreen()),
                (int)Math.sqrt(l*c1.getBlue()*c1.getBlue()+r*c2.getBlue()*c2.getBlue()));
    }

}