Yeah, I know you’re all convolution experts now. But, I still think I can show you something you didn’t know about convolution. So far I’ve shown how you can use convolution to smooth the edges in an image, but did you know you can also use convolution to find the edges? Yep, that’s right! You can do a whole lot of cool stuff with convolution. So, let’s start with a new big thing:
As you can probably tell, this big thing starts off low-and-even, then suddenly becomes high-and-even (i.e. all 5’s then all 15’s). This is an example of an ‘ideal’ strong edge – in the real world though, edges are usually uneven and noisy. Now let’s take a look at a new kernel:
Since this kernel adds up to ‘0’, we don’t have to do any division at the end (if you are having trouble remembering what I am talking about, refer to the first two articles on convolution: One, Two). Now, let’s apply this kernel to our big thing and see what we get:
See what happened? All the flat parts gave a ‘0’ result, and the area that had a big transition (i.e. 5-to-15; the ‘edge’), resulted in a big spike. Now, let’s try it on our old friend Mr. Bug:
OK, it’s not really the ghost of Mr. Bug, but, the ‘edge map’ of the Bug does look pretty ghostly doesn’t it?
In Machine Vision, edge detection can be a powerful tool because it allows us to extract structural information about objects in an image. In other words, edges help to show us the shape of objects. Once we have information on the shape of an object, we can use that shape information to determine if the object is one we recognize.
About this article: Bob’s Imaging Fundamentals is an article series based on the work of Bob Howison. Originally titled Bob’s Brain Snacks, these articles were intended to help employees and partners get up to speed with the fundamental concepts of image processing. They became such a popular reference that we’ve decided to bring them to the Possibility Hub. As technology goes further, faster, and new industries discover the power of digital imaging, it’s important to remember the basics.
Bob’s Brain Snacks are recommended for anyone interested in learning about imaging technology. Sharpen your mind and try one!