GB1166542A - Improvements in or relating to Character Recognition Systems - Google Patents

Abstract

1,166,542. Character recognition. MULLARD Ltd. 29 March, 1968 [13 Feb., 1967], No. 6873/67. Heading G4R. A character thinning system applies two intersecting raster scans to a character to find points lying substantially at the centre of character strokes or parts. A character, stored as a digitized matrix, is scanned in a horizontal and in a vertical raster, the raster pitches being comparable to stroke width so that scanned rows and columns of the matrix are separated by a number of unscanned rows and columns. During each scan, the co-ordinates of the centre point of each series of four or more consecutive black (character) points are noted (an isolated white point being treated as black). Any two centre-points, one from the vertical raster and one from the horizontal, which are too close together are next replaced by a new centre point midway between them. All surviving centre points are now joined by straight line segments by starting at one centre point, finding the two remaining centre points nearest to it and the two nearest to each of the latter (excluding the last two already used) and constructing all segments between these points which are " compatible " with the character i.e. do not pass through more than two consecutive white points. The straightest two-segment line found is extended by successive application of the " two nearest points " technique and segment construction, priority being given to branches which are closest to the original direction. When such a branch ends, other branches are extended in a similar way until all compatible segments between centre points have been constructed to form a line-thinned character (consisting of the segments) which is used for recognition and is also displayed together with the original character. The above algorithm is executed by suitably programming a computer. Line ends, junctions and loops detected during the thinning are retained for use in the recognition. As a modification, the character may be undigitized, the centre points being obtained as minima, but the centre points are then processed digitally as above.