SURVEILLANCE SYSTEM

Abstract: A surveillance system comprises a number of video cameras (12) connected to a central control (10). Video information is converted to digital format and stored in a disc drive (36). A comparator (42) is used to detect movement within the field of view of the cameras (12), and detection of movement causes the relevant images to be retained, the stored data otherwise being discarded. Stored images can be viewed on a domestic television set by being retrieved via a D/A converter (46) and a modulator (47).

Description: Surveillance System This invention relates to a surveillance system, and relates particularly, but not exclusively, to a surveillance system employing closed-circuit television ("CCTV"). Television-based surveillance systems are known for the remote monitoring of locations which are difficult to access and/or require high levels of security, eg bank vaults and nuclear facilities. However, such known systems are expensive and require human supervision on a continuous or regular basis. Consequently, these known systems are unsuitable for uses where low cost and reliable automation are paramount requirements. According to the present invention there is provided a surveillance system comprising at least one sensor adapted to survey a predetermined location and to produce a sensor output signal from which a visually representable image of the location may be derived; a motion detector adapted to produce a trigger signal upon detection of motion within the location; and a recorder adapted to record a visually representable image signal of the location derived from the sensor output signal; in which operation of the recorder to record a signal for subsequent reproduction is activated by the trigger signal. The surveillance system may comprise a plurality of sensors each disposed to survey a respective predetermined location or to survey a predetermined location from respective perspectives. The or each sensor may produce a respective sensor output signal which varies with variations in occupancy of a respective location or with variations in occupancy of the predetermined location as perceived from its respective perspective and/or with variations in positioning of entities at the respective location or with variations in positioning of entities at the predetermined location as perceived from its respective perspective. The or each sensor is preferably a television or video camera; the or each sensor may function at wavelengths which are visible or invisible to normal human sight. The surveillance system may further comprise suitable illumination means, for example one or more lamps (which may be infra-red lamps) disposed to illuminate the location(s). The or each sensor may be mounted in a manner allowing its direction of view to be changed, preferably by remote operation. For example, the direction of view of one or more of the sensors may be changeable by local servo-motors under remote control, preferably from a controller. The or each sensor is preferably provided with an automatic shutter or other light-baffling means responsive to excessive levels of incident light to reduce, filter or block excessive light or other radiation from affecting operation of the sensor (eg if the sun shines directly into the camera) . A signal processor may be coupled to receive the sensor output signal. The signal processor may form part of the motion detector; it may analyse the sensor output signal and produce the trigger signal on detection of motion within the location. This analysis may comprise comparison of the sensor output signal over time. The signal processor and the or each sensor are preferably mutually synchronised; more preferably, they are mutually synchronised at the frame rate of the sensor, for example, at the frame rate of the television system where the or each sensor is a television camera. The sensor output signal from the or each sensor (or a signal derived therefrom) may be continuously recorded, preferably with overwrite, in the absence of a trigger signal from the signal processor and without overwrite upon the production of a trigger signal from the signal processor. This may facilitate recording of signals immediately preceding the production of a trigger signal without the recording medium requiring to be of indefinite length. The signal processor preferably functions by sampling the output signal from the or each sensor at a predetermined point or set of points in the respective field of view, and comparing the sampled signal values with respective previous sampled signal values to ascertain if an output signal has varied to an extent requiring the production of a trigger signal. Control means preferably permits the system user to select a particular camera (or other sensor) from a plurality of cameras (or other sensors) forming part of the system for display of a picture from that particular camera independently of the production of trigger signals by the signal processor to enable real- time surveillance of a user-selected location. The surveillance system is preferably adapted for local operation or remote operation (which may be conducted, for example, via any suitable form of telemetry link). An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of one example of a surveillance system in accordance with the invention; Fig. 2 is a block diagram showing parts of the system of Fig. 1 in greater detail; and Fig. 3 is a schematic illustration of a number of systems operating together. Referring to Fig. 1, a surveillance system intended particularly for domestic use comprises a central control unit or "video panel" 10 to which are connected four video cameras 12. The cameras 12 are mounted in suitable positions to survey, for example, the four exterior sides of a house, or four rooms within the house, or some combination of these. For minimal complexity and cost it is preferred to use monochrome cameras, although colour could be used. Suitable cameras for the purpose are Model 5400 by Vision Limited of Edinburgh, Scotland.. The video panel has an input 14 for connection to a conventional TV antenna, and an output 16 for connection to the aerial input of a conventional domestic television set. A video (non-modulated) signal may also be provided at output 18. The video panel may suitably be installed in a secure location, for example beneath a floor, to prevent unauthorised access. A small user display 20 is installed in an accessible location, such as beside the TV set, and suitably comprises a LCD or photodiode display providing information to the householder, such as whether an alarm condition has been activated, its date and time, and the camera(s) concerned. A user control 22 is provided in the form of a portable handset communicating with the user display 20 by a conventional infrared link. The system is powered from the mains at the video panel 10 as indicated at 24. A standby power supply 26 may optionally be connected to the video panel 10 to maintain the system in the event of failure of or malicious interference with the mains supply. The system may also optionally include motorised pan/tilt mounts 28 for one or more of the cameras 12, and illuminators 30 for illuminating the field of view of one or more of the cameras 12; the illuminators 30 may be infrared lamps if the cameras used are IR sensitive. Referring to Fig. 2, each of the cameras 12 (only one shown in Fig. 2) is connected to the video panel 10 by a simple four-core cable 32 (six-core where a pin/tilt mechanism is used) . The operation of the cameras and generation of trigger signals is controlled by a controller 34, which may be a standard industrial microcontroller; one suitable arrangement is to form the microcontroller 34 from a combination of PIC 16C71 and PIC 16C54, both by Arizona. The controller 34 generates clock pulses which are used to synchronise the system. In particular, the clock pulses are used as frame sync signals for the cameras 12; since the system is operating as a stand-alone system in monochrome and carrying only basic video information, it does not require more complex control signals such as colour burst signals, and non-interlaced frames may be used. Preferably, the controller 34 operates on a 4MHz clock, and the cameras operate at 25 frames per second with an image resolution of 312 x 287 pixels. The controller 34 acts as a switch to repetitively scan the video signals from the connected cameras 12 and passes the received video information to store in the form of a conventional computer hard disc drive 36, via an A/D converter 38 and a conventional disc drive controller 40. The arrangement is such that video signals are recorded continuously, but overwrite pervious signals unless motion is detected by at least one of the cameras. Motion detection, in this embodiment, is carried out by time interval examination of the video output from each camera, using a simple comparison circuit 42. This is achieved by comparing two parts of the image from time separated frames, a first part being in the centre of the image and a second part being at an edge of the image. If the two second parts have amplitudes which are not equal (or are not within a predetermined tolerance) it is assumed that a signal change has been caused by some ambient condition, such as a change in sunlight in the area. If the two second parts have amplitudes which are equal (or are within a predetermined tolerance) it is assumed that ambient conditions are unchanged, and the two first areas are then compared. If these two are not within a predetermined tolerance, it is assumed that motion has occurred within the picture area, and the comparator 42 generates a motion signal 44 which causes the disc drive controller 40 to retain the video information for a given time interval around the motion detection. Other forms of motion detection may be used to control the retention or discarding of the video information, for example by separate PIR detectors separately wired to the central control. The user can replay stored video images over the domestic TV set. For this purpose, the video panel 10 includes a D/A converter 46 which may be used to convert the stored video back into analog format, and a modulator 47 to provide a broadcast-type signal. The retrieved images may then be viewed on any TV set connected to the aerial downlead. The generation of a motion signal can readily be used to provide an indication alerting the user, such as a visual or audible alarm at the user control 22. It is also a simple matter to attach date and time indications to the recorded images. The system may be readily adapted to be monitored and controlled from a variety of locations. In a single dwelling, for example, there may be a conventional television set in each of a number of rooms, and each of these can have a user display associated with it for use with a single cordless control. The system is also readily capable of networked use, for example in a neighbourhood watch operation among adjacent homes. Referring to Fig. 3, each of a number of houses 50 is provided with a system indicated at 52 in accordance with the invention, interlinked in a linear fashion by cable 54. Each house 50 may have a physical switch 56 in the circuit to give an assured privacy option, and access to the video information in any given house from any other given house may be protected by password. In effect the networked system operates in a similar manner to any computer local area networ . Reverting to Fig. 2, the video panel 10 may include a conventional modem 48 allowing the system to be controlled and to transmit information over a standard telephone line. While live, real-time video could not be transmitted over a standard telephone line, it is readily possible to transmit control signals and alarm indications, and to transmit stored video frames at a relatively slow rate to allow remote inspection of the nature of any incident causing an alarm. Images can be transferred down the phone line at high and low frame rates. At high frame rates motion can be observed and a quick review of the premises archive can be made. However, to obtain the full information from the archive a slower frame rate is selected by means of the telephone key pad. The fast frame rate is one frame a second. The slow frame rate is one frame every four seconds. The " preferred embodiments of the invention therefore allow the integration of: 1) a multi-camera switch; 2) a camera pan & tilt control; 3) a motion detection system; 4) a recording means; 5) a user friendly means of control; and 6) the facility to monitor and control the entire system from any number of local and remote locations The system is capable of being implemented in a very simple manner and at low cost. The process of generation of playback field synchronous pulses by micro-controllers allows multi-TV standard or other form of viewing screen operation and recording and playback of information. The recording of video data separated from its synchronisation fields allows for lossless data compression techniques. The process of permanently recording data only when motion or a change of status is detected in the camera's field of view ensures efficient use of the recording device. The use of digital disk media as distinct from tape based methods for recording minimises the time delay between an event trigger and the start of the recording process. Continuous recording of data provided by the camera(s) allows capture of pre-trigger events. The integrated design allow for expansion into remote telemetry access, for example, telephone, cellular phones, fibre-optic radio and other electromagnetic wave means. Images stored on the archive contain all the information captured by the cameras. Unlike other techniques no information is removed to optimise the storage. The resultant images, being in a digital format, can be replayed as often as required without deterioration. They are in an ideal format for computer video enhancement.

Claims: _!_____ 1. A surveillance system comprising at least one sensor adapted to survey a predetermined location and to produce a sensor output signal from which a visually representable image of the location may be derived; a motion detector adapted to produce a trigger signal upon detection of motion within the location; and a recorder adapted to record a visually representable image signal of the location derived from the sensor output signal; in which operation of the recorder to record a signal for subsequent reproduction is activated by the trigger signal. 2. A surveillance system according to claim 1, comprising a plurality of sensors each disposed to survey a respective predetermined location or to survey a predetermined location from respective perspectives. 3. A surveillance system according to claim 1 or claim 2,in which the or each sensor is a television or video camera; and functions at wavelengths which are visible or invisible to normal human sight. 4. A surveillance system according to any preceding claim, in which the or each sensor is mounted in a manner allowing its direction of view to be changed. 5. A surveillance system according to any preceding claim, in which the or each sensor is provided with an automatic shutter or other light-baffling means responsive to excessive levels of incident light to reduce, filter or block excessive light. 6. A surveillance system according to any preceding claim, including a signal processor coupled to receive the sensor output signal. 7. A surveillance system according to claim 6, in which the signal processor forms part of the motion detector. 8. A surveillance system according to claim 7, in which the signal processor analyses the sensor output signal and produces the trigger signal on detection of motion within the location. 9. A surveillance system according to claim 8, in which said analysis comprises comparison of the sensor output signal over time. 10. A surveillance system according to claim 9, in which the signal processor and the or each sensor are mutually synchronised at the frame rate of the sensor. 11. A surveillance system according to any of claims 7 to 10, in which the sensor output signal from the or each sensor (or a signal derived therefrom) is continuously recorded with overwrite in the absence of a trigger signal from the signal processor and without overwrite upon the production of a trigger signal from the signal processor. 12. A surveillance system according to any of claims 7 to 11, in which the signal processor functions by sampling the output signal from the or each sensor at a predetermined point or set of points in the respective field of view, and comparing the sampled signal values with respective previous sampled signal values to ascertain if an output signal has varied to an extent requiring the production of a trigger signal. 13. A surveillance system according to any of claims 7 to 12, including control means operable by a system user to select a particular camera or a plurality of cameras forming part of the system for display of a picture from that particular camera independently of the production of trigger signals by the signal processor to enable real-time surveillance of a user- selected location. 14. A neighbourhood surveillance system comprising a plurality of surveillance systems according to any of the preceding claims serially interconnected and operating in synchronism. 15. The system of claim 14, in which each individual surveillance system is provided with privacy switch means operable to prevent the output of its sensors being transmitted to the other systems.

Inventors: WILLIAMS SIMON RUSHBROOK, WILLIAMS, SIMON, RUSHBROOK
Applicants: MERYON INSTR LIMITED, WILLIAMS SIMON RUSHBROOK, MERYON INSTRUMENTS LIMITED, WILLIAMS, SIMON, RUSHBROOK
Application year: 1996
Main classification: G08B13
IPC codes: G08B13