GB1338287A - Pattern classifying apparatus - Google Patents

Abstract

1338287 Character recognitions systems INTERNATIONAL BUSINESS MACHINES CORP 1 Dec 1971 [7 Dec 1970] 55703/71 Heading G4R In a character or pattern recognition system a signature word representing the pattern is compared with a reference word which may identify the pattern and if the difference or distance between the words exceeds a certain value a class word, from which the reference word is derived, is modified and a further comparison made. The class word is successively modified until a preset difference is obtained, the reference word then indicating the correct class of the character. Signals from the character scanner pass via a pre-processor to a store 210, Fig. 2. From the store groups of signals representing portions of of the character field, i.e. sub-patterns, are passed to respective logic modules 220. There may, for example, be 32 modules. Each module provides a single bit indicative of whether or not a particular feature is present in the corresponding sub-pattern. The bits form a 32-bit signature word representing the character. The signature casues a 6-bit trial class (or position code) word to be generated by a unit 241 which in turn causes unit 243 to generate a trial reference word. The reference word has 32 bits and lies at a distance of at least 16 from each other reference word. The trial reference word and the signature are compared at 244 and cause the trial code word, and hence the trial reference word, to be modified if necessary. When the distance between the compared words is less than 8 the current trial class word is deemed to identify the pattern. This word is passed to store 260 together with the distance value. The class word may be translated into a suitable code, e.g. ASCII, if required. A processor employs the class word and distance value, the latter determining how much reliance may be placed on the accuracy of the identification of the pattern. The logic modules may be binary decision trees, Fig. 4-7 (not shown), or may be structured in a computer program. Units 241-244 may also be structured in a program, Figs. 8, 9 (not shown). In one such structure the bits in each of a number of pairs of fields selected from the signature are compared. Dependent upon the number of mismatches a corresponding 5-bit trial class word is selected and a 32-bit trial reference word constructed from this. The trial reference word and the signature are compared and, dependent on the number of mismatches, the trial class word is modified by addition of a sixth bit, this word now identifying the pattern if the distance between the reference word and the signature is less than 8. Another structure makes use of the fact that most signatures will have a distance 0 or 1 from one of the possible reference words. This structure attempts to form a class word by a procedure involving the comparison of 8-bit bytes of the signature with the initial 8-bits of each reference word. Should the procedure determine that no reference word exists for which the distance is 0 or 1 it is then necessary to compare the signature with all of the reference words.