Patent GB-976741-A (GB)
Title: End of character detector
IPC: G06V10/26
Filed: 1963-09-13
Abstract: 976,741. Automatic character reading. SPERRY RAND CORPORATION. Sept. 13, 1963 [Sept. 24, 1962], No. 36165/63. Heading G4R. In a character reading apparatus similar to that described in Specification 939,433 in which signals derived from scanning the character are applied to correlation networks, one for each possible character, and a threshold circuit detects a recognition response from any correlation circuit, the circuit for identifying the circuit giving the highest response is enabled by means counting the number of scans which detect black areas after the threshold circuit has responded and giving an enabling signal when a predetermined count has been reached. The character is imaged on to the screen of a camera tube by a light flash and scanned on a raster of parallel strokes. The video signal is amplified and clipped, applied to a temporary store and applied as a series of groups of samples to correlation circuits. When the character is almost fully scanned the corresponding correlation circuit gives a maximum output. All the correlation outputs are applied through an OR gate 118 Fig. 3 to the threshold detector 124 the output 40 of which is applied to a flip-flop 62 Fig. 2. The other output of detector 124 biases off diodes 122 to allow the correlation signals to be stored in capacitors 126. The quantized video signal is applied to AND gate 78 with clock pulse, the horizontal sweep signal HS and a signal G from flip-flop 80 which is set by clock pulse 4 and react by clock pulse 29. There are 40 clock pulses per scan, the period from 4 to 29 covering the scan area. An output on lead 68 indicates a "black" sample in the scan. The signal K from flip-flop 62, indicating that the threshold device has given a signal, and the video signals on lead 68 are applied to AND gate 66. The output indicates a black signal in a scan after the threshold signal and it is applied to flip-flop 70 which gives an output for each such stroke. These are counted in counter 72 and a matrix circuit 74 responds to a predetermined count e.g. six to give a "read" command on lead 52. This is'applied to OR gate 60. A black signal on lead 68 also sets flip-flop 82 and its unset output is applied with signal K to AND gate 86. The output of this gate therefore indicates a completely white stroke after the threshold signal. Flip-flop 88 is set and provides a read command for application to OR gate 60. After the first character, further means provide read command signals by counting clock pulses in counter 92. There may be 15 scans covering the character area so that a count of 600 after the last recognition signal indicates that the character area has been fully scanned. Matrix circuit 94 responds to this count and gives a read command on lead 56, also applied to OR gate 60. It also responds to a count of 40, giving a signal indicating the completion of each stroke and these are counted at 98, matrix 100 responding to the count of fifteen to give a fourth read command signal on lead 58. This is also applied to OR gate 60. The first read command to appear passes on lead 106 to be gated with the K signal in AND gate 102 and sets the read flip-flop 104. The output on lead 46 starts a stair-case voltage generator 128 Fig. 3 which raises the voltage on all the capacitors 126 together. The one carrying the highest charge is first to exceed the threshold of the associated trigger 112. As soon as one of these is set detector 132 switches the generator off, leaving a marking on a single lead identifying the character. The white stroke detector detects the end of a character if it is properly separated from the following character. If characters are joined by smudging the black stroke counter detects the approximate position of the end. If both fail the pulse and stroke counters estimate the position of the end and give the read command. The read command also causes reset of the various storage flipflops and counters in the circuit of Fig. 2.