Handwritten text segmentation using average longest path algorithm

Offline handwritten text recognition is a very challenging problem. Aside from the large variation of different handwriting styles, neighboring characters within a word are usually connected, and we may need to segment a word into individual characters for accurate character recognition. Many existing methods achieve text segmentation by evaluating the local stroke geometry and imposing constraints on the size of each resulting character, such as the character width, height and aspect ratio. These constraints are well suited for printed texts, but may not hold for handwritten texts. Other methods apply holistic approach by using a set of lexicons to guide and correct the segmentation and recognition. This approach may fail when the lexicon domain is insufficient. In this paper, we present a new global non-holistic method for handwritten text segmentation, which does not make any limiting assumptions on the character size and the number of characters in a word. Specifically, the proposed method finds the text segmentation with the maximum average likeliness for the resulting characters. For this purpose, we use a graph model that describes the possible locations for segmenting neighboring characters, and we then develop an average longest path algorithm to identify the globally optimal segmentation. We conduct experiments on real images of handwritten texts taken from the IAM handwriting database and compare the performance of the proposed method against an existing text segmentation algorithm that uses dynamic programming.

1. Introduction

Offline handwritten text recognition has a wide range of applications, such as automatic bank check processing and handwritten postal address recognition. One major challenge in handwritten text recognition is that neighboring characters within a word may be connected when written, as shown in Fig. 1. Many OCR tools are built to recognize individual characters [7], [15], [22], [8]. As a result of this, to achieve handwritten text recognition, we often need to segment a connected word (or words) into individual characters [18], which we call handwritten text segmentation in this paper.