Rotation and size invariant shape recognition apparatus

1,077,564. Automatic pattern recognition. INTERNATIONAL BUSINESS MACHINES CORPORATION. June 28, 1965 [July 8, 1964], No. 27239/65. Heading G4R. In apparatus for identifying shapes, the outline of a shape is followed to obtain vertical and horizontal displacement waveforms, these are converted to binary numbers representing successive directions and from these a train of binary numbers is produced representing successive changes in direction, ten of these numbers at equal steps round the periphery are entered into a shift register and recirculated for comparison with stored representations so as to eliminate the effects of orientation. The shape is traced three times, x and y waveforms being produced each time. The speed of movement round the periphery is constant so the time taken to return to the starting point is a measure of the length of the periphery. In the first trace this time is converted to a D.C. voltage which is used to control the frequency of a pulse generator (70, Figure not shown) so that it produces ten sampling pulses in each of the next two traces. The x and y signals are differentiated to obtain the corresponding speeds of movement and these are combined at (30) to obtain a signal (30a) representing the one of sixteen sectors of a circle which contains the tangent to the trace at each instant. The direction representation is converted in diode matrix (40) to a combination of four binary bits which signals are applied to a subtractor (50) directly and through fixed delays. The output (50a) from the subtractor represents in four bits and a sign bit, the change of direction during the period of the delays 60a-60d). These values are entered with the shift registers (60-64) under the control of the ten equally spaced shift pulses from circuit (70). The scan traces twice round the periphery of the shape so that the values in the shift registers recycle completely being compared in each position with stored values in circuits (100, 101 &c.). When a match is indicated, a corresponding latch (110, 111 &c.) is set and whenthe control circuitry (90) indicates that the third tracing is complete the latches are read out via And gates (116, 117 &c.) and then reset. If more than one identification signal is produced circuit (120) blocks the readout gates. Instead of circuits (100, 101 &c.) built to respond to predetermined patterns, the contents of the shift registers may be compared with corresponding reference signals read out from a store.