The salient ones for separating particular shapes are determined by inductive learning during the construction of classification trees. There is a feature for every possible geometric arrangement of local topographic codes. The arrangements express coarse constraints on relative angles and distances among the code locations and are nearly invariant to substantial affine and non-linear deformations. They are also partially ordered, which makes it possible to narrow the search for informative ones at each node of the tree.
Different trees correspond to different aspects of shape.
Joint induction of shape features and tree classifiers. Doc 41 Boosting performance in neural networks - Drucker, Schapire et al. Doc 2 Handwritten segmented characters - Garris, Wilkinson et al. The graph only includes citing articles where the year of publication is known.