GB2308260A

GB2308260A - Video recording equipment

Info

Publication number: GB2308260A
Application number: GB9525601A
Authority: GB
Inventors: Alec Moses Messulam
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-12-14
Filing date: 1995-12-14
Publication date: 1997-06-18
Also published as: GB9525601D0

Description

Video Recording Equipment The present invention relates to video recording equipment that has particular application in security systems.

Closed circuit television cameras are well known for monitoring premises and security systems often also include video cassette recorders (VCR'S) to record the video image.

The difficulty with such systems is the fact that the cassette can only record for a limited length of time.

To allow continuous recording, expensive dedicated VCR's are available that automatically recycle the cassette when the end is reached. Apart from their cost, such VCR's may on some occasions write over a cassette containing required information.

An alternative solution has been to use a form of time lapse photography rather than continuous video in order to compress the amount of information stored on the cassette.

Once again this requires dedicated recorders and the series of still images produced can sometimes be blurred.

A problem with both these types of equipment is that it takes a long time to review a cassette and because one is constantly watching the same scene, it is easy to overlook a few frames containing vital information.

With a view to mitigating the foregoing disadvantages, the present invention provides video recording equipment comprising a video camera, a video recorder connected to record the scene viewed by the video camera, means for generating live digital signals representative of the scene currently viewed by the camera, a memory for storing digital signals corresponding to a reference scene, and a computer operative to compare the digital signals stored in the memory with the live digital signals and to activate the video recorder in the presence of a significant difference between the stored signals and the live signals.

The entire video recording equipment may be self contained in that it may comprise a modified camcorder (i.e. a combined camera and recorder) . Camcorders are currently available that have a digitiser and record the scene in digital format on cassette. The invention may be implemented in this case by incorporating a memory and a micro-computer into the camcorder forming a self contained unit that records only changes in a scenes and ceases to record during intervals when the viewed scene matches the scene stored in memory.

Another possibility is for the camera and the recorder to be a conventional analogue camcorder and for the digitising of the video signal to be carried out by a separate computer.

There are currently available for personal computers digitising boards, also termed video capture boards, that sample the analogue video output signal and convert it into a digital form for storage and subsequent processing. In this case the equipment would comprise a camcorder, connected to a programmed personal computer that includes a video capture board and controls the switching on and off of the video recorder. The memory for the reference frame would in this case form part of the memory of the personal computer.

In a still further possibility, the camera and the recorder are not combined and a suitable recorder is connected to a programmed personal computer containing a video capture board. In this case, the camera may be a conventional surveillance camera and the recorder may either be a VCR or any other recording medium onto which the computer can write, for example a magnetic hard disk, a magneto-optical disk or an optical disk (CD-ROM).

The reference scene may be permanently set by the operator of the equipment but in this case if an object should enter the scene of surveillance and remain there, then the recorder will be switched on to operate constantly and risk exhausting the capacity of the recording medium. For this reason, it is preferred that the reference scene should be automatically updated from the live scene, whenever it is sensed by the computer that no change has taken place within the monitored scene for a predetermined length of time.

There are currently available computer programs, for example Photoshop , for editing image files. Such programs can with minor modification be used in the analysis of the live image in that they can automatically compensate for changes in brightness and contrast caused by changes in ambient illumination. After a match has been achieved, a pixel by pixel comparison may be carried out to determine from the distribution of pixels in which a change has occurred the size and even the shape of the intrusion into the monitored scene. A numerical output can then be computed to indicate the size of the intrusion and the recorder may be switched on if the computed value exceeds a threshold. It is also possible to compute the X-Y co-ordinate values of the centre of mass of the intrusion and if the size and the centre of mass do not change over a length of time then the recorder may be switched off and the scene last recorded transferred into memory to be used as the reference scene thereafter.

If the invention is implemented using a computer that is physically separate from the camera and has other means of entering data into it, such as a keyboard and a mouse, then it is possible to mask from within the viewed scene areas that are outside the area of surveillance. This is advantageous in that when monitoring for example a forecourt, a camera will almost invariably also see passing traffic outside the area to be protected and by masking such areas, it is possible to reduce or eliminate unnecessary triggering of recorder.

With image editing programs, it is possible to alter the image magnification on the screen, in other words, the program can compute the pixel values of a zoomed image. When an intrusion is detected, it is therefore possible for automatically to control the camera to zoom the camera lens to enlarge the image of the intrusion that is recorded while continuing to compare the viewed scene with the corresponding computed values for the zoomed reference scene.

If the camera is mounted on a motorised support, it is also possible to rotate the camera in order to keep the centre of mass of the intrusion always within the field of view while recording is taking place. In this case, it is possible to store several reference images each corresponding to a different angle of view of the camera.

If the camera has been rotated or its lens zoomed, then the computer should restore the settings to cover the entire area of surveillance before switching off the recorder and registering the modified scene in the reference image memory.

Though the detection of an intrusion can occur within one frame of video, responding to a single frame may cause false detection and it is preferable to await confirmation from two or more consecutive before switching on the recorder. In addition to this delay, a significantly longer delay will occur between the time that the recorder is switched on and recording taking place. To mitigate this disadvantage, it is desirable to use an image buffer that constantly stores the video signal to be recorder for a sufficient length of time to ensure that an intrusion is recorder at all times that it falls within the area of surveillance.

Though the invention finds primary application in security systems, it can also be used in wild life photography or in monitoring equipment used for scientific purposes. For example, movement of animals can be recorded automatically by an unattended camera.

Camcorders commonly have the ability to record time and date thereby allowing a complete record of movement within a surveillance area to be recorded over prolonged time periods using only a conventional recording cassette.

The invention will now be described further, by way of example, with reference to the accompanying drawing which is a block schematic diagram of a video recording equipment of the invention.

In the drawing, there is shown a video monitoring equipment comprising a camera 10 the video output signal of which is supplied to a digitiser 12. The output of the digitiser 12 is fed to a computer 16 that includes a frame memory 14. The computer compares the live signals from the digitiser 12 with the signals stored in the frame memory 14 and produces output signals to control a recorder 18 and optionally the camera 10.

There are various possibilities for implementation to make use of equipment currently available in the market. In a first embodiment, the camera 10 and recorder 18 may be a conventional analogue camcorder, the computer 16 and frame memory 14 may be a conventional personal computer (e.g. IBM &commat; compatible or Apple Mac &commat;), or a mini computer (Sun &commat;, VAX 0, DEC 0 etc.) and the digitiser may be a video capture board. In a second embodiment, the camcoder may be a digital camcorder incorporating the digitiser 12 and connected to a separate computer. Lastly, a digital camcorder may be modified to include a dedicated micro-computer and a frame memory. A still further possibility is to form a dedicated video capture board that includes video memory, a processor and a preprogrammed control chip.

When the equipment is first switched on, the camera is correctly positioned, pointed, zoomed and focused to cover the area to be monitored. The equipment is then set in its security mode and the computer 16 acts to record the digitised image of the first scene in the frame memory 14.

Thereafter, each live frame of signals is compared with the stored frame under the control of a program stored in the computer 16. The comparison serves to identify pixels (picture elements) that have changed from the pixel stored in the frame memory 14. The program can disregard slow changes by performing a periodic normalisation of the stored image to compensate for changing light conditions. In other words, before comparison is effected on a pixel by pixel basis, the brightness and contrast of the two images are matched so that the computer may match like with like.

The image area within which data is analysed can be restricted using masking techniques common in image editing software. Apart from reducing false triggering of the recorder, such masking reduces the amount of data that needs to be processed making it easier to perform the analysis in real time.

The computer then produces a count of the number of pixels that have changed and analyse their distribution to determine if this is consistent with a large object, such as a vehicle or a human being, entering the monitored area. If the size of the concentrated mass of an intrusion, that is the number of changed pixels bunched together, is sufficiently large then the computer switches on the recorder 18 in order to record the nature of the intrusion.

The computer also monitors the centre of mass of the intrusion, that is to say the co-ordinates of the pixels about which all changed pixels are equally distributed and records this value. Should the size of an intrusion and its position not change for a length of time, say five seconds, then the current digital image is written by the computer 16 into the frame memory to be adopted as the reference image, the recorder 18 is switched off. In this way, if a car should be driven into the monitored area and left there by its owner, the recorder will remain on only for five seconds after the driver has left the scene and the reference image will now contain the car. Its time and date of arrival can be recorded in the camera in the normal manner. If the car should later be removed, then once again the time of removal will be recorded and the reference scene five seconds later will return to its original form.

Because the position of the centre of mass of the intrusion and the size of the intrusion are known by the computer, it is possible for it to steer the camera if the latter is mounted on a motorised support, and to control the zoom setting of the camera lens to provide a more detailed recording of the intrusion. This is valuable if a thief is to be identified from the recording. After an intrusion has been detected and recorded, it is necessary to return the camera to its normal zoom and position settings before storing a fresh reference image in the frame memory 14.

The computer may additionally switch on infrared lights to improve the image quality during recording. Cameras can operate to sense intrusions in very low light values but the wide lens aperture required limits the depth of field.

Improving the illumination by infrared lighting improves contrast and image clarity without alerting the intruder. Of course, if it is desired to alert the intruder to act as a deterrent then visible lights can be switched on rather than infrared lights.

Because the intrusion detection in the present invention is carried out by image analysis, it is relatively easy to determine if the equipment has been broken or rendered ineffective, for example by spraying foam into the lens. In such a case, there will be no image or an image that is permanently out of focus and either of these conditions can readily be used to generate an audible alarm to indicate that the monitoring equipment is not functional.

It is possible to store compressed video information on a magnetic hard disk. In this case, recording can commence almost immediately and it is preferred when a hard disk is available to the computer to use it, as least in the first instance, to record the video information. Alternatively, one may use a buffer memory to store video information so that no frames should be lost between detection of a change in the monitored scene and the activation of the recorder.

The same buffer memory may also act to avoid recording of a stationary scene once it is determined by the computer that the image from the camera has become static.

As there is no need to detect smaller intrusions into the monitored area, the image stored in the frame memory need only be a low resolution image. This considerably reduces the processing power necessary to analyse the live digital data for detection of an intrusion thereby allowing the analysis to be carried out in real time using currently available hardware.

Claims

1. Video recording equipment comprising a video camera, a video recorder connected to record the scene viewed by the video camera, means for generating live digital signals representative of the scene currently viewed by the camera, a memory for storing digital signals corresponding to a reference scene, and a computer operative to compare the digital signals stored in the memory with the live digital signals and to activate the video recorder in the presence of a significant difference between the stored signals and the live signals.

2. Video recording equipment as claimed in claim 1, wherein the entire equipment may is self-contained in that it may comprise a modified camcorder.

3. Video recording equipment as claimed in claim 1, wherein the camera and the recorder are constituted by analogue camcorder, the camcorder being connected to a separate computer that includes a frame memory.

4. Video recording equipment as claimed in claim 3, wherein the camcorder includes a digitiser and is operative to record data in digital format, video data being supplied in digital format to the computer.

5. Video recording equipment as claimed in claim 3, wherein the camcorder generates an analogue output signal and the computer includes a video capture board for converting the analogue video signals into digital format.

6. Video recording apparatus as claimed in any preceding claim, wherein the reference scene is permanently set in the frame memory under-the control of the equipment operator.

7. Video recording equipment as claimed in any of claims 1 to 6, wherein the reference scene is automatically updated by the computer from the live scene, whenever it is sensed by the computer that no change has taken place within the monitored scene for a predetermined length of time.

8. Video recording equipment as claimed in claim 7, wherein the computer is operative to calculate the size and the position of the centre of mass of areas in the live image signals that differ from the stored image signals and to determine that a scene is not changing when the size and centre of mass do not change for a predetermined length of time.

9. Video recording equipment as claimed in claim 8, wherein the computer is connected to control the zoom setting of the lens of the camera to magnify the image of any intrusion into the monitored scene that is registered by the recorder.

10. Video recording equipment as claimed in claim 8 or 9, wherein the camera is mounted on a motorised support and the computer is operative to steer the camera to centre any detected intrusion in the image registered by the recorder.

11. Video recording equipment as claimed in any preceding claim, wherein means are provided for electronically masking regions of the monitored image that are processed by the computer, the computer only responding to changes occurring with unmasked regions.

12. Video recording equipment as claimed in any preceding claim, wherein a signal buffer is provided as the input of the recorder to prevent loss of data between detection of an intrusion in the monitored area and commencement of recording.

13. Video recording apparatus constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawing.