Regulated Array Grammars of Finite Index. Part II: Syntactic Pattern Recognition

We introduce special k-head finite array automata, which characterize the array languages generated by specific variants of regulated n-dimensional context-free array grammars of finite index we introduced in the first part of this paper. As a practical application we show how these analyzing devices in the two-dimensional case can be used in the field of syntactic character recognition. 1 Bridging the gap between theory and practice The first part of this paper laid some theoretical foundations concerning regulated array grammars of finite index (with various regulation mechanisms) and cooperating/distributed array grammar systems with prescribed teams. (We will not repeat the definitions of these mechanisms in this second part.) We concentrated on questions concerning the equivalence of different definitions regarding their descriptive capacity. In this second part of our paper, we will focus on practical, especially algorithmic aspects of the problem of recognizing handwritten characters by means of certain array grammars, roughly describing a recognition system which is currently under development; prototype versions running on personal computers can be obtained by contacting the second author. One of the advantages of such syntactic methods for character recognition is the fact that they describe certain typical features of the characters instead of comparing characters bit by bit with a reference character. This may lead to recognition algorithms which are less font-sensitive, see [8, page 274]. On the other hand, recently the authors have considered bounded parallelism within array grammars [I-7] on practical grounds. This feature can nicely be formulated in terms of cooperating/distributed array grammar systems with prescribed teams as introduced in part I of our paper. In practical applications of these theoretical models as for character recognition the number of active areas processed in parallel is quite limited. Hence, our theoretical models of regulated array grammars of finite index are fitting quite well for being applied in the field of syntactic character recognition. Part II of our current paper is organized as follows: In the next section we address the important stages on the process of syntactic character recognition. In the third section we discuss some problems arising when going from theory to reality, e.g., when going to implement a tool based on the theoretical model of n-dimensional array grammars with prescribed teams of finite index. In the fourth section we elaborate how array grammars with prescribed teams can be interpreted as analyzing mechanisms, which then leads us to the definition of n-dimensional k-head finite array automata. The implementation of a prototype for the syntactic analysis of hand-written (upper-case) characters based on twodimensional k-head finite array automata is discussed in the fifth section. A short summary concludes the paper. The bibliography is just a supplement of the one given in the end of part I of the paper. 2 Aspects of syntactic character recognition In this section we give a short overview of the stages in syntactic character recognition and of the data used in our practical experiments. 2.1 Data acquisition Hand-written characters were acquired from hundreds of persons on specific forms and then scanned in order to obtain a digital pixel image. A reference to the database obtained in that way can be found in [3].