Extracting the components' contours

Images generally contain representations of objects. One of the goals of image analysis is to identify and extract these objects. In object detection/recognition applications, the first step is often to produce a binary image that shows you where certain objects of interest could be located. No matter how this binary map is obtained (for example, from the histogram back projection we did in Chapter 4, Counting the Pixels with Histograms, or from motion analysis as we will learn in Chapter 11, Processing Video Sequences), the next step is to extract the objects that are contained in this collection of 1s and 0s.

Consider, for example, the image of buffaloes in a binary form that we manipulated in Chapter 5, Transforming Images with Morphological Operations, as shown in the following figure:

We obtained this image from a simple thresholding operation followed by the application of open and close morphological filters. This recipe will show you how to extract...