Television based security system - detects picture changes by comparing received pictures with those stored on video tape

摘要

An alarm is given if any significant difference is detected. Several cameras, each possibly in a different part of a building are time multiplexed and their outputs are checked against the contents of a single video tape. The video tape is endless and is fed round two spools. When a particular camera is switched through the tape is fed round and the corresponding picture is read. The outputs are then compared and an acoustic or visual alarm given if the difference in signals exceeds some fixed threshold. If this occurs, the camera concerned is also switched to another monitor for permanent viewing. The information is held on the video tape in diagonal tracks, with the ten images repeated several times round the endless loop of tape.