Patent GB-1495334-A (GB)
Title: Method and means for electronic image analysis within a raster-scanned field
IPC: G06M11/04
Filed: 1975-01-20
Abstract: 1495334 Image analysis CARL ZEISS-STIFTUNG [Trading as CARL ZEISS] 20 Jan 1975 [25 Jan 1974] 2332/75 Heading G1A Image analysis apparatus comprises: scanning means for providing a video signal representing objects to be analyzed; a discriminator 1 for providing a signal A of a length corresponding to the chord of an object, the discriminator output A being connected both directly and via a one lineperiod delay T 1  to an anti-coincidence pulse generator 6; a local search signal generator 10 (or 28) for providing a search signal B timed to occur during a chord; a first delay line 16 receiving the A signal and having time-spaced output taps connectable by a switch 15 to respective input taps of a second delay means 17, 19 providing a second delay variable between a predetermined time T 2  and a line period T 1 , depending on the progress of signals through the delay line 16 at the instant of switch 15 closure; a device 11, 8 for generating an output signal C upon the first occurrence of an output from the second delay means 17, 19; means for closing the tap-switches 15 by means of the output signal C; and means 7 for generating an evaluation output signal 21 when the anti-coincidence pulse and the output signal C coincide. The discriminator 1 provides a steady output A as long as the brightness of the object chord being scanned lies between lower and upper limits defined by threshold levels 2, 3, the A signal being represented by horizontal chords as shown in Fig. 3. If adjacent chords fail to overlap, the anticoincidence pulse generator 6 provides one input to an AND gate 7. With a switch 9 closed as shown, a chord-length discriminator 10 generates a signal B having a start delayed with respect to the A signal and occurring only if the chord exceeds a predetermined length, as shown in Fig. 4. Each B signal, via an OR gate 11, sets a bi-stable 8 to provide an output signal C to close the switch bank 15, so that the first portion of an A signal on any output tap of the line 16 is transferred to the line 17 and thence to the line 19, whence it emerges after a delay which is equal to or less than one line period, to provide, via the OR gate 11 and the bi-stable 8, a C signal to anticipate or replace the B signal, as illustrated in Fig. 5. When, in later scans, the C signal closes the switches 15 before the leading edge of the A signal has entered the line 16, that leading edge is delayed, from the time it arrives, by a full line period T 1  to initiate the C signal for the next following line, as illustrated in the lower part of Fig. 5. The final C signal 22 Fig. 5 is operative during the generation of an anti-coincidence pulse at 6, Fig. 1, and is then terminated by the resetting of the bi-stable when the end of the last A signal, delayed in the line 5, denies both inputs to an NOR gate 20. Just before than, while the AND gate 7 is still enabled by a C signal, the anti-coincidence pulse generator 6 emits an object count pulse 21. The C signals are also used to enable an AND gate 12 to pass A signals into evaluation means 29 where chord lengths are summed to estimate the area of the object. As alternative to the length discriminator 10, a manual search signal generator 23 may be selected by opening the switch 9 and closing a switch 28. The generator 23 supplies signals for searching a rectangle manually controllable by height and width controls 25, 26 and by a position joy-stick 27, the search area being brightened on a TV monitor. An alternative embodiment Fig. 2 (not shown) differs from that of Fig. 1 in details of the delayline and tap-switch construction.