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Building Machines That See: Finding Edges in Images

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By Eric Gregori
Senior Software Engineer
This article was originally published at EE Times' Design Line. It is reprinted here with the permission of EE Times.

With the emergence of increasingly capable low-cost processors and image sensors, it’s becoming practical to incorporate computer vision capabilities into a wide range of embedded systems, enabling them to analyze their environments via image and video inputs.

Products like Microsoft’s Kinect game controller and Mobileye’s driver assistance systems are raising awareness of the incredible potential of embedded vision technology. As a result, many embedded system designers are beginning to think about implementing embedded vision capabilities.

In this article, the second in a series, we introduce edge detection, one of the fundamental techniques of computer vision. Like many aspects of computer vision, edge detection sounds simple but turns out to be complex. We explore some of the common challenges and pitfalls associated with edge detection, and present techniques for addressing them. Then, after explaining edge detection from an algorithmic perspective, we show how to use OpenCV, a free open-source computer vision software component library, to quickly implement application software incorporating edge detection. For an overview of computer vision and OpenCV, read "Introduction to Embedded Vision and the OpenCV Library."

What is an "Edge" in Computer Vision?

Images, of course, are made up of individual points called pixels. In a grayscale image, the value of each pixel represents the intensity of the light captured when creating the image. An edge is defined as an area of significant change in the image intensity. Figure 1 below shows a grayscale image on the left, with its corresponding binary edge map on the right. If you look carefully, you will notice that the white lines in...