Patent GB-1201349-A (GB)
Title: Television surveillance system
IPC: G07C3/14
Filed: 1967-12-18
Abstract: 1,201,349. Burglar alarms; pattern recognition. JACKSON & CHURCH ELECTRONICS CO. Inc. 18 Dec., 1967 [30 Dec., 1966; 30 Nov., 1967], No. 57313/67. Headings G4N and G4R. [Also in Divisions G1 and H3] A field of view is monitored for variations of light intensity indicative of e.g. an intruder by scanning the field television-wise, sampling the video signal periodically, comparing the amplitude of the sampled video signal with the average of the samples for that point in n preceding scans, registering a suspicion signal if there is any substantial difference and giving an alarm when the suspician signal for a point rises above a predetermined level. The monitoring television camera 11, Fig. 1, receives scanning signals from a digital sweep generator 12, see Fig. 3 (not shown); The video signals are sampled by a circuit 13 at times determined the timing circuit 12 and the samples are held on a capacitor for digitizing. The samples may be initiated by pulses from the timing circuit or by apertures in a mask located in front of the camera tube. The digital signals are processed in a logic circuit 17 and if a sufficiently suspicious signal arises an audible or visual alarm is given to an operator who may view the output from the camera on a monitor 21. A plurality of cameras at different stations may use the same logic circuit on a time sharing basis. Logic circuit 17 compares the sample value with the average of the sample for the corresponding points in the previous 8 frames. If the difference exceeds a first amount a count of 8 is put in a suspicion register, and if it exceeds a second greater amount a count of 12 is entered. If such a suspicion arises at an adjacent point in the next line or frame a suspicion count of 16 or 32 respectively is entered. Simultaneous signals from other alarm devices may be entered in the suspicion register with a weighting dependent upon their reliability. The alarm is given when the suspicion count for any point rises above a first preset value or more than a preset number of points have a suspicion count above a lower preset value. The suspicion count is reduced by one each frame so that the alarm is not given in response to an accumulation of noise. An alarm is also given if the overall brightness or contrast are outside a predetermined range. Pattern comparison.-A standard pattern is first scanned and the intensity value for each sample point is built up over a series of eight scans in a delay line memory 110, Fig. 6, by comparing the stored values with the digitized intensity signal from converter 62 by two's complement addition 106-108 the difference +#I being used to update the stored value. Switches 462, 463, 464 and 468 are changed over and a pattern to be checked is scanned. The intensity of the sample points is compared with the stored values again by two's complement addition at 106-108 and the absolute value of the difference #I is compared with a reference R 1  and if |#I| > R 1 , and alarm 469 is operated or sorting means may be actuated. The standard pattern is stored in the delay line store 110 is not amended by #I at this stage but instead recirculates through switch 464.