Television-based alarm system
First Claim
1. An alarm system for detecting a movement or change in the field of view supervised by a television camera, the system comprising a discriminator responsive to the video signal produced by the camera and adapted to produce a signal upon the occurrence of a predetermined characteristic in the picture content of the video signal, means for providing a succession of reference values each derived by adding the number of signals produced by the discriminator during a plurality of equal time intervals of predetermined duration and dividing the sum so formed by the number of time intervals over which the addition is performed, difference value means for generating difference values between the number of signals produced by the discriminator during each of a succession of time intervals, each time interval equal to the said predetermined duration, and the currently provided reference value, comparing means for comparing the difference values with a preselected first value to produce an event signal, and evaluating the event signal according to a predetermined criterion to produce an alarm with the criterion is satisfied.
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Abstract
The invention concerns an alarm system for detecting a movement or change in the field of view supervised by a television camera. A discriminator, for example an edge discriminator or an amplitude discriminator, produces a signal upon the occurrence of a predetermined characteristic in the picture content of the video signal from the camera. The number of such signals occurring during each of a plurality of successive television fields is compared with a reference value which is periodically updated. The reference value is derived by counting the total number of signals occurring during a plurality of field periods preceding that for which the comparison is effected and dividing the total by the number of fields thereby generating an arithmetical mean value. Each comparison generates a difference signal which is further evaluated to determine whether a relevant variation in the field of view of the camera has occurred, whereupon an alarm is released.
36 Citations
10 Claims
- 1. An alarm system for detecting a movement or change in the field of view supervised by a television camera, the system comprising a discriminator responsive to the video signal produced by the camera and adapted to produce a signal upon the occurrence of a predetermined characteristic in the picture content of the video signal, means for providing a succession of reference values each derived by adding the number of signals produced by the discriminator during a plurality of equal time intervals of predetermined duration and dividing the sum so formed by the number of time intervals over which the addition is performed, difference value means for generating difference values between the number of signals produced by the discriminator during each of a succession of time intervals, each time interval equal to the said predetermined duration, and the currently provided reference value, comparing means for comparing the difference values with a preselected first value to produce an event signal, and evaluating the event signal according to a predetermined criterion to produce an alarm with the criterion is satisfied.
Specification