Patent GB-1334249-A (GB)
Title: Pattern recognition system
IPC: G06V30/162
Filed: 1970-12-14
Abstract: 1334249 Character recognition systems ELECTRONIC READING SYSTEMS Inc 14 Dec 1970 [15 Dec 1969 27 Nov 1970] 59385/70 Heading G4R In a character recognition system signals are developed, by way of optical or electronic filters having parameters varying in a certain way along the scanning aperture, which instantaneously represent the zero, first, and second, moments of the part of the character presently being scanned. Further signals are developed from these moment signals, certain of the signals being compared with reference signals characteristic of reference characters to determine the identity of the character scanned. The embodiment disclosed employs a stationary slit viewing a vertical slice of the character, the whole of the character traversing the slit as the document is transported continuously past the slit, Fig. 3 (not shown). The document is a web carrying characters which are transparent on an opaque background, or vice versa. Light from the slit is directed on to three photo-cells via respective filters. The transmittance of one filter is uniform over its length (corresponding to the length of the slit), of another the transmittance varies linearly, and of the third the transmittance varies with the square of the distance from one end of it. The photo-cells respectively present signals S#, S1, S2 representing the zero, first and second moments of the solid area of the slice of the character being viewed. The light from the slit is also sensed by an array of photo-cells such that at least one views a part of the character and another one a part of the background. The output of this photo-cell array is used to develop signals representing the contrast ratio of the character and the maximum opacity of the background. The signals S#, S1, S2, are passed to difference amplifiers (67, Fig. 6, not shown) fed also by the background and contrast signals to compensate for contrast variations. A timing generator (74) generates a signal (E74) representing the distance (X) of the slit from the left hand edge of the character. By use of a multiplier (76) a signal S3 representing the first horizontal moment about the left hand side of the character is derived from S# and X. Similarly the second moment S4 is developed by a multiplier (80) from S# and X<SP>2</SP>. Signals S#-S4 are applied to integrator stores (80-84). Additionally S#, S1 pass to peak voltage detector stores (85, 86); S#, S1, S2 pass to minimum voltage detector stores (90-92); and S#, S1, S3 pass to gated integrators (94-96) which integrate and store the signals for a brief period encompassing the instant at which S# is maximum. The outputs of all these stores, representing various parameters of the character such as its solid area, maximum solid height &c., as detailed in the Specification, are fed to an arithmetic unit (100). This unit computes various parameters of the character related to its centroid, centre of gyration, width &c. Further circuitry, Fig. 6C (not shown), is fed with S#, S1, S2 and develops from them signals indicating parameters such as the presence of single slope lines (e.g. as in N) and of double slope lines (e.g. as in D or in C). These parameter signals, together with those from the arithmetic unit, are passed in binary form to a decoder (65) which determines the identity of the character. Reference is made to the use of a variable length slit and to the use of a cathode ray tube scanner. Instead of a single photo-cell associated with a respective filter a line of photocells may be used, with their outputs electronically weighted to simulate the effect of the filter. The photo-cells may receive reflected rather than transmitted light. It is stated that the circuitry can be simplified by use of a detector which determines the width and maximum solid height of the character prior to it being scanned by the photo-cells. This may be accomplished by means of a preview slit or by scanning the character twice.