6.3. Active contours (snakes)
6.3.1. Basics
Active contours or snakes [Kass88] are a completely different approach to feature extraction. An active contour is a set of points which aims to enclose a target feature, the feature to be extracted. It is a bit like using a balloon to ‘find’ a shape: the balloon is placed outside the shape, enclosing it. Then by taking air out of the balloon, making it smaller, the shape is found when the balloon stops shrinking, when it fits the target shape. By this manner, active contours arrange a set of points so as to describe a target feature, by enclosing it. Snakes' original formulation was as an interactive extraction process, though they are now usually deployed for automatic feature extraction.
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