TestUtils.java

package test;

import java.awt.image.BufferedImage;

public class TestUtils {

    public static double imagePercentDiff(BufferedImage img1, BufferedImage img2) {
        //from http://rosettacode.org/wiki/Percentage_difference_between_images#Java
        int width1 = img1.getWidth(null);
        int width2 = img2.getWidth(null);
        int height1 = img1.getHeight(null);
        int height2 = img2.getHeight(null);
        if ((width1 != width2) || (height1 != height2)) {
            return 100.0;       //if width and height mismatch, just count it as complete failure
        }
        long diff = 0;
        for (int y = 0; y < height1; y++) {
            for (int x = 0; x < width1; x++) {
                int rgb1 = img1.getRGB(x, y);
                int rgb2 = img2.getRGB(x, y);
                int r1 = (rgb1 >> 16) & 0xff;
                int g1 = (rgb1 >> 8) & 0xff;
                int b1 = (rgb1) & 0xff;
                int r2 = (rgb2 >> 16) & 0xff;
                int g2 = (rgb2 >> 8) & 0xff;
                int b2 = (rgb2) & 0xff;
                diff += Math.abs(r1 - r2);
                diff += Math.abs(g1 - g2);
                diff += Math.abs(b1 - b2);
            }
        }
        double n = width1 * height1 * 3;
        double p = diff / n / 255.0;
        return p * 100.0;
    }

}