Highlight differences between images

Question

There is this image comparison code I am supposed to modify to highlight/point out the difference between two images. Is there a way to modify this code so as to highlight t

Answer 1

This solution did the trick for me. It highlights differences, and has the best performance out of the methods I've tried. (Assumptions: images are the same size. This method hasn't been tested with transparencies.)

Average time to compare a 1600x860 PNG image 50 times (on same machine):

• JDK7 ~178 milliseconds
• JDK8 ~139 milliseconds

Does anyone have a better/faster solution?

public static BufferedImage getDifferenceImage(BufferedImage img1, BufferedImage img2) {
    // convert images to pixel arrays...
    final int w = img1.getWidth(),
            h = img1.getHeight(), 
            highlight = Color.MAGENTA.getRGB();
    final int[] p1 = img1.getRGB(0, 0, w, h, null, 0, w);
    final int[] p2 = img2.getRGB(0, 0, w, h, null, 0, w);
    // compare img1 to img2, pixel by pixel. If different, highlight img1's pixel...
    for (int i = 0; i < p1.length; i++) {
        if (p1[i] != p2[i]) {
            p1[i] = highlight;
        }
    }
    // save img1's pixels to a new BufferedImage, and return it...
    // (May require TYPE_INT_ARGB)
    final BufferedImage out = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
    out.setRGB(0, 0, w, h, p1, 0, w);
    return out;
}

Usage:

import javax.imageio.ImageIO;
import java.io.File;

ImageIO.write(
        getDifferenceImage(
                ImageIO.read(new File("a.png")),
                ImageIO.read(new File("b.png"))),
        "png",
        new File("output.png"));

Some inspiration...