Change detection

You now have a good grasp of working with remote sensing data using GDAL, NumPy, and PIL. It's time to move on to our most complex example: change detection. Change detection is the process of taking two geo-registered images of the exact same area from two different dates and automatically identifying the differences. It is really just another form of image classification. It can range from trivial techniques like those used here to highly sophisticated algorithms that provide amazingly precise and accurate results.

For this example, we'll use two images from a coastal area. These images show a populated area before and after a major hurricane, so there are significant differences, many of which are easy to spot, making these samples good to learn change detection. Our technique is to simply subtract the first image from the second to get a simple image difference using NumPy. This is a valid and often used technique. The advantages are that it is comprehensive and very...