GB2402829A

GB2402829A - Surveillance image recording system

Info

Publication number: GB2402829A
Application number: GB0313325A
Authority: GB
Inventors: Clive Richard Andrews; Kevin Michael Jarvis; Terrence Michael Burns
Original assignee: EQUIPE ELECTRONICS Ltd
Current assignee: EQUIPE ELECTRONICS Ltd
Priority date: 2003-06-10
Filing date: 2003-06-10
Publication date: 2004-12-15
Also published as: GB0313325D0

Abstract

A surveillance image recording system comprises at least one camera 10 arranged to capture images of a scene. A comparator 13 allows captured frames to be compared with preceding frames in order to determine regions of variation. Selective removal of invariant image information enables only data representing changes to be stored, for example upon a disc 16, thereby occupying less memory whilst avoiding loss of surveillance detail. Encoded time data stored with the images enables scenes to be retrieved according to temporal indexing using a computer 23.

Description

SURVEILLANCE IMAGE RECORDER

This invention relates to the storage of moving images from surveillance or CCTV system cameras onto computer storage media.

Recording of moving images *om surveillance cameras onto both videotape and computer systems is well established. Because surveillance systems produce a lot of video information when no events of interest are occurring, there is a recognised need to remove information of no significance before recording in order to avoid having to change videotape Frequency or, in the case of computer system storage, to record over a useful period of time. One method is to detect activity in the camera images and stop recording when nothing happens. Anodher medhod is to remove complete video *ames such that only one camera image is stored *om a sequence of many. This method is often used with multiple cameras such that one image *om each camera is selected in turn for storage. Additional reduction in the storage space required is also achieved using established moving image compression techniques for limited bandwidth transmission systems found in telephony communication. These techniques, examples of which are known commercially as MPEG and ITU-T H.263, remove potentially important surveillance information in images as well as redundant information in order to achieve a bandwidth limit.

Removal of either video *ames or image content by compression can severely degrade the effectiveness of a surveillance system. A missing *ame can be the important one where an intruder's face was looking towards a camera. Bandwidth limiting compression degradation reduces the clarity of an image, which could result in facial detail being lost. Bandwidth limiting compression also makes use of redundant information shared by successive *ames such that single images or "still *ames" are not reproducible. For this reason a combination of *ame removal and bandwidth limiting compression are not effective when used together. <

According to the present invention there is provided a means to store all image information from one or many television cameras without loss of either video frames or image detail, whilst only elements of any frame that is actually different to the preceding frame are stored. By this means, only the minimum necessary information to completely reconstruct the significant parts of moving image information is stored. During replay all relevant picture information is reconstructed.

By storing image data with time and date information onto computer disc, this invention provides the means to rapidly search, find and reconstruct images from any one of many cameras over a large period of time without loss of information.

An embodiment of the invention is now described by way of example with reference to the accompanying drawing showing the main functional blocks in which: Figure 1 illustrates the main components and connections required to record filter and store surveillance data onto computer disc; Figure 2 illustrates the main components and connections required reconstruct and display surveillance data previously stored on computer disc.

Figure 3 illustrates the use of multiple cameras Referring to the drawing, signals from camera 10 in Figure 1 are converted to digitised signals by one or more analog to digital conversion devices 11, each having an output buffer memory 12. Under control of computer 23, the first image to be stored in the output buffer 11 is passed straight through image comparator 13 into an image frame store 17 and simultaneously through encoder 14 into output data buffer 15, from whence it is transferred onto the computer storage disc system 16. Subsequent images are compared by compactor 13 with the image held in the frame store 17 and only picture elements (pixels) that vary according to a predetermined threshold level are transferred through encoderl4 to the output data buffer 15 and to the frame store 17. Only if the total number of pixels is above a second predetermined threshold number will the output data buffer contents then be transferred to disc signifying that an important event has taken place and the image should be recorded. If there is not sufficient change to reach this threshold then the output data buffer 15 is cleared ready for the next image data. All data passed to the output data buffer 15 is coded by encoder 14 to locate the position of changed pixels within the image and is preceded by a header containing date, time and camera number information. Once an event from a particular camera has started recording, increments may continue to be recorded for a predetermined number of frames after the changes have fallen below the threshold. When recording has stopped, a complete initial frame will be recorded at the beginning of the next event.

The image comparator 13 operates by comparing the brightness and colour, if a colour camera is used, of individual pixels of camera images with the corresponding pixels stored in the image frame store 17. A decision is calculated from the difference in brightness or colour between these two pixels and the predetermined threshold that may be set by means of computer 23.

There is also a facility to mask areas of the image frame store 17 by means of the computer 23 such that changes in successive pixels are ignored by the pixel comparison and hence changes in masked areas will not cause pixels to be stored.

Reconstruction of an image taken from any camera at a particular time requested by an operator is achieved by first locating the corresponding timed and dated header on disc 16 in Figure 2 via computer 23. A decoder 21 recreates initial images in image store 22 that may be viewed by display monitor 24. Subsequent frames are updated in the image store 22 by the incremental data that was stored on the disc in the recording process described above.

An embodiment of the invention when used with more than one camera is shown in Figure 3.

For each additional camera 101...10N (where N is the total number of cameras -1), items 11,12,13,14,15 and 17 are also repeated and shown as 111,121,131,141,151 and 171 as many as N times. llN, 12N, 13N, 14N, 15N and 17N show the final repetition. Each camera is thus served by a quite independent motion detection system, elimination of redundant repeated data and coding of the recorded data. This is a modular configuration that lends itself to simple expansion as cameras are added. A header identifying the camera number and recording time precedes all data recorded.

The invention may be adapted for surveillance data transmission and reconstruction including subsequent remote storage across a low bandwidth link by replacement of the disc storage 16 by a transmission device in Figure 1 and a receiving device in Figure 2. The transmitting device draws data from buffer 15 at a rate compatible with the transmission media. Fluctuations in the generation rate of transmitted data are removed by storage of peaks (such as initial frames) in the buffer 15 memory. - 4

Claims

1. A surveillance imagery storage system comprising TV camera, analog to digital conversion, image store and a digital image comparison means that eliminates information that has not changed from the preceding image prior to storage taking place.

2. A surveillance imagery storage system as claimed in claim 1 wherein date, time, and image changes are digitally encoded for efficient data storage on computer media such as a hard disc drive.

3. A surveillance imagery storage system as claimed in claim 1 where a plurality of cameras and associated analog to digital conversion, image store and digital image comparison means are each associated with digital encoding of date, time, and image changes with the corresponding camera number prior to storage on computer media such as a hard disc drive.

4. A viewing system comprising decoding of data stored in the manner of claim 1 and claim 2 or claims where data from an image store is used to add to the decoded data in order to reconstruct the previously recorded images. The viewing system includes a conventional computer display monitor.

5. A viewing system as claimed in claim 4 where an original camera number is detected from the stored data and used select image data from a specific camera for display on the computer display monitor.

6. A viewing system as claimed in claim 4 of claim 5 where a computer is used to search out specific recorded sequences taken at a particular time and by a particular camera.

7. A recording system as described in claims 1,2 or 3 with an added capability to mask an area of image memory that should not take part in any image comparison process in order that a continuously moving and uninteresting part of the scene - such as a ceiling fan in a room for example - should not result in storage of changing but unimportant image data.

8. A recording system as described in claims 1,2 or 3 that is adapted for transmission of image data over low bandwidth data link such as telephone or ISDN communication networks.

9. A surveillance imagery storage system substantially as described herein with reference to figures 1-3 of the accompanying drawing. - 6