The shape of handwritten characters

Abstract

A handwritten character magically survives serious distortions in size, orientation and even structure, justifying perhaps its Sanskrit name--Aksharam, the undecaying. Several traditional approaches model characters in terms of certain shape features like line crossings, T-junctions etc. But there is no sanctity in the choice of these features--which may be specific to a script--nor is there a limit to their number. We address the general problem of defining the shape of a 2D line diagram, with character as a significant special case. To this end we develop a framework based on a branch of mathematics known as the Catastrophe theory. A small set of 11 shape features is derived systematically from our framework. The 11 features are found in several of world's scripts and may in fact be universal. More complex shapes break down to the above 11 in handwritten scripts. We discuss how our model can be applied to on-line character recognition from pen-based devices.