Finding Differences in Images and Documents

By Charles Nichols

Can you find the differences?

How about now?

Pretty obvious now, eh?

The solution. Did you find them all?

Cheek Bones

BeltOrnaments

Sash Color

SandalStrap

PavementCracks

Balls

Chimney

Bow Switched

Sides

Anklet

Sash Length

ImageJ software from the National Institutes of Health, link:

http://rsbweb.nih.gov/ij/download.html

Calculator Plus plug in:

http://rsbweb.nih.gov/ij/plugins/calculator-plus.html

How did I do it? Using free software.

Download the image and note its size, 600w 672h. http://blogs.baruch.cuny.edu/fro12dtg/files/2012/11/Assassins-Creed-Revelations-game-600x672.jpg

The image is mirrored down the middle, so each image is 600w x 336h. Save these sections separately and label as Top and Bottom using your favorite image editor.

Create the Reverse Image by putting Top on Bottom and Bottom on top.

Open ImageJ software after installing the Calculator Plus plugin.

Step 1: Create a Reverse Image

Step 2: Subtract the Images

- =

Original Image Reversed Image Result, after auto contrast

This is referred to as background subtraction.

Step 3: Multiply the Result by Itself

x =

Subtracted Image Subtracted Image Result, after saturation

Step 4: Overlay images, making white transparent and washing out the original.

+ =

Washed Out Image Subtracted Image Result, after auto contrast

Small details were skipped, but can be figured out pretty quickly.

Here’s another example from a Geocache. Differing numbers indicate coordinates:

That’s It!

Solution:

That’s It!

These are misalignment errors.

Misalignment errors were caused by one or two pixel offsets in the baseline image.

Here, a baseline image was given and had to be manually aligned for all ten digits.

Here’s the baseline. Try it yourself!

Misalignment Errors

If you can do it with images, you can do it with a video an in real time!

Check out these videos:

Telecommunications and Imaging Laboratory

Institut Montefiore - University of Liege, Belgium

http://www2.ulg.ac.be/telecom/research/vibe/

Other Uses for this Method

Detecting Changes in Documents is Easy