Patent GB-1009404-A (GB)
Title: Improved character recognition apparatus
Inventor: MAXBY RALPH DAVID
IPC: G06V10/10
Filed: 1961-08-28
Abstract: 1,009,404. Automatic character reading. SOLARTON ELECTRONIC GROUP Ltd. Aug. 24, 1962 [Aug. 28, 1961], No. 31003/61. Heading G4R. In character recognition apparatus the character is scanned and the eleme ntary areas of the character field are adjudicated black or white by comparing the density of each area with a combination of the density of a pair of areas on each side and the mean density of a number of areas. The characters are specially shaped to comprise combinations of vertical and horizontal strokes and in the main embodiment sensing is by a row of seven photo-cells X, A, B, C, D, E, Y, Fig. 2, arranged at 45 degrees and scanned rapidly downwards over the character, the character moving comparatively slowly. An optical system for performing this scan consists of a rotating drum carrying a series of mirrors adapted to sweep images of the character successively over a line of photocells. A scale rotating with the drum is sensed to obtain clock pulses and end-of-scan signals. In its movement the character comes into proper horizontal register where, as shown in Fig. 2, the end two cells X, Y do not cross the character. This condition may be detected to enable the recognition circuit to operate or a recognition may be taken as sufficient indication that the character is properly registered. The seven leads are taken to circuits of the kind shown in Fig. 8 where lead A is applied through resistor 45 to the grid of triode 40 of a long-tailed pair and the neighbouring cell leads X and B are applied through equal resistors 50, 51 to the grid of the other triode 41. All seven leads are connected to an adder 54 and the output integrated at 53 to provide a signal indicating the density over at least part of the field sensed by the row of photo-cells. This signal is also applied, through resistor 52 to the grid of triode 41. It is prevented from falling to zero by a bias voltage applied through a diode 55 to prevent the background signal ever being passed as " 1". The triode 41 will normally be conducting, reducing the voltage across the triode 40. When the signal on lead A rises to a certain value above the combined signal on the grid of triode 41, triode 40 will conduct and pass a " black " signal to the gate 57. The gates 57 take 13 samples, shown as rows in Fig. 2, and enter the binary values into shift registers 60-64. There are only five stages in each register so that only five of the thirteen row signals are stored but this is sufficient to extract four shape elements by gates 66-69. A horizontal line produces signals in the first stage of register 60, the second of register 61 and so on. A vertical line produces five signals in the same register, register 60 for a left-hand stroke, register 64 for a right-hand stroke and register 62 for a central stroke. As scanning proceeds, a succession of nine groups of five rows produce a corresponding sequence of feature signals on the four leads. The features are stored in corresponding shift registers and recognition is achieved by gating appropriate combinations together for the different characters. There is also a gate which detects whether any character at all has been sensed and if a corresponding recognition signal is not present a reject signal is produced to stop the document. The gates 66-69 may pass partly defective characters by being arranged to respond to four out of five necessary signals. Other scanning arrangements are suggested, for example scanning on a slanting raster by means of a C.R.T. and storing or delaying each scan signal to obtain the equivalent of the parallel outputs from the seven photo-cells. Alternatively a fixed row of photo-cells 100, Fig. 1 may sense the whole character as it moves quickly underneath. To avoid interference with other characters the row may be divided into a number of short lengths, Fig. 13b. Other photocell arrangements are described. Specifications 850,582 and 917,574 are referred to.