Percentage difference between images

Compute the percentage of difference between 2 JPEG images of the same size. Alternatively, compare two bitmaps as defined in basic bitmap storage.

Useful for comparing two JPEG images saved with a different compression ratios.

You can use these pictures for testing (use the full-size version of each):

import java.awt.image.BufferedImage;
import javax.imageio.ImageIO;
import java.io.IOException;
import java.net.URL;
 
public class ImgDiffPercent
{
  public static void main(String args[])
  {
    BufferedImage img1 = null;
    BufferedImage img2 = null;
    try {
      URL url1 = new URL("<Your Image1 Location on WEB>");
      URL url2 = new URL("Your Image2 Location on WEB");      img1 = ImageIO.read(url1);
      img2 = ImageIO.read(url2);
    } catch (IOException e) {
      e.printStackTrace();
    }
    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)) {
      System.err.println("Error: Images dimensions mismatch");
      System.exit(1);
    }
    long diff = 0;
    for (int i = 0; i < height1; i++) {
      for (int j = 0; j < width1; j++) {
        int rgb1 = img1.getRGB(i, j);
        int rgb2 = img2.getRGB(i, j);
        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;
    System.out.println("diff percent: " + (p * 100.0));
  }
}