Features for shape representation

Shape information provides useful representations for an object, often sufficient for its recognition. In particular, shape information can be found at points where there is a change in an otherwise continuous gradient or where the direction of the contour changes more rapidly. Moreover, also symmetry plays an important role. We briefly describe two methods respectively devoted to the extraction of feature points on the contour, and to the extraction of mediai lines of gray-tone patterns. The feature points linked successively to each other constitute a significant approximation of the perceived shape, while the mediai line accounts for the symmetries in the pattern and is located along the regions having locally higher intensity.