GB2395551A

GB2395551A - Self calibrating surveillance system

Info

Publication number: GB2395551A
Application number: GB0226939A
Authority: GB
Inventors: Michael Mainds
Original assignee: Baxall Ltd
Current assignee: Baxall Ltd
Priority date: 2002-11-19
Filing date: 2002-11-19
Publication date: 2004-05-26
Anticipated expiration: 2022-11-19
Also published as: GB0226939D0; GB2395551B

Abstract

A surveillance system comprises one or more surveillance cameras 11 linked to a control station 12 at which the images produced by the camera 11 can be viewed and processed to provide information on the absolute sizes of objects in the image. The system is self calibrated by processing of a captured image to identify the relative position and relative size of known objects in the image. Stored statistical information on the size distribution of the known objects is used to calculate a scaling factor which is then used to calculate the dimensions of unknown objects in the images. Processing of the images may be performed within the camera or at the control station. The surveillance system may also use a fixed object within the image of known size to calculate absolute size values, and may be operative to calculate the height and angle of inclination of the camera.

Description

239555 1

Surveillance System This invention relates to a surveillance system and more particularly to a self calibrating surveillance system.

Surveillance systems are well known and usually consist of a 5 plurality of closed circuit television (CCTV) cameras linked to a central control station at which the images from the cameras are monitored by control station staff. A typical such installation is where a plurality of cameras are placed strategically around a town or city and these cameras are linked to a control station which is manned 24 hours a day by staff 10 who monitor the images received from the cameras and who can raise the alarm or alert the authorities for example if they witness a crime being À committed or a fire.

The problem with such systems is that the image provided to the J À.. À central monitoring station from the cameras are not in anyway calibrated À 15 whereby the absolute size of objects in the image can be determined. In À. Àe order to overcome this problem, it is possible for each camera to be À individually calibrated such that an absolute indication of the size of objects in the image can be determined. This is however a time consuming and difficult job particularly where a large number of cameras 20 are required to be calibrated which may be a relatively large distance apart. The present invention has been developed in an attempt to overcome this problem and allow such cameras to essentially calibrate

themselves. In this way, even a large number of cameras can be easily calibrated to allow the absolute size of objects in an image to be determ ined.

Thus and in accordance with the present invention therefore there 5 is provided a surveillance system comprising at least one monitoring device operable to produce video images of a surveillance area, the at least one monitoring device being linked to a control station where said video images can be viewed, said system further including an image processing means which acts to identify the relative position and relative 10 size of known objects in said image for which a statistical distribution of size is known and which calculates a scaling factor therefrom, said À A. scaling factor being calculated for each position of known objects in said A. image whereby the scaling factor can be applied to unknown objects in À the said image to give an absolute indication of size.

À - 15 With this arrangement, it is possible to provide a system which is À À À. essentially self calibrating and which is capable of generating absolute À values of sufficient accuracy for the size of objects regardless of their position in the image.

The invention will now be described further by way of example only and with reference to the accompanying drawings in which: Figure 1 shows a diagrammatic representation of a single surveillance camera and an example of the image produced by the 5 camera; and Figure 2 shows a diagrammatic representation of the operation of one embodiment of surveillance system in accordance with the present invention.

The surveillance system of the invention comprises one or more 10 surveillance cameras 11 which are linked to a control station 12 at which the image which is produced by the camera can be viewed and processed À I. to provide information relating to objects in the image.

Àe The or each surveillance camera 11 comprises a closed circuit I. À : television camera 11 (CCTV) which preferably operate digitally.

À lS Alternatively, the or each camera 11 can be of any other suitable form of À. À : camera or imaging device as desired or as appropriate.

À The control station 12 is provided at a location remote from the or each camera 11 and is capable of receiving images from the surveillance areas covered by each camera 11 and processing the images, if desired or 20 if necessary. The control station 12 will usually be computer or microprocessor based.

Alternatively, the image produced by the or each camera 11 and can be analysed and processed within the camera 11 itself and then

simply transmitted or otherwise sent to the control station 12 for monitoring. The or each camera 11 is linked to the control station 12 by a link 13 which allows the transmission of many images, in some cases in the 5 form of a video stream, at an acceptable rate. Thus, for example, the link 13 may be a wireless link of suitable form or a hardwired link of any appropriate form. In the former case, it is envisaged that the link 17 may be microwave based and in the latter case it may comprise a suitable electronic universal serial bus (USB).

10 The system operates as follows: The or each surveillance camera 11 in the system provides a À. Am. continuous stream of video images to the control station 13 via the link 13. The control station 12 captures a single image from the stream of ) a.e À : video images received from the or each camera 11 for analysis.

À 15 The position of known objects in the image, for example people, À À. : are identified and stored by control station 12 along with an indication of À the relative heights of these known objects detected in the captured image. Position information is recorded as a relative distance from the camera compared to the position of other known object in the image.

20 Once image data for a statistically sufficient number of objects has been recorded, the size of objects in the image can be identified using the fact that the statistical distribution of the relative sizes of detected objects at the same relative distance from the camera should be identical

- 5 for each relative distance from the camera at which objects have been detected. Using this statistical analysis of the relative height of objects at each relative distance from the camera, it is possible to identify objects in the image which should be of the same size. Therefore from this 5 information, is possible for the control station to determine a scaling factor which should be applied to objects at different relative positions from the camera. Once the control station 12 has calculated a scaling factor, it is possible to calculate the absolute size of the object at any relative distance position in the image by use of the scaling factor.

10Alternatively, if there is a fixed object in the image which is of ,, known size, this can also be utilised to provide absolute size values for - 6, objects contained within the image.

It will also be appreciated that once the control station 12 has À , : calculated a scaling value for distance and an absolute size for the object, À 15 by the application of simple trigonometric principals, the height of the . : camera and the angle of inclination thereof can be calculated very simply.

À The ability of the system to essentially self calibrate even a single camera offers a number of significant advantages over existing systems.

For example, if such a system is being used for security reasons, it 20 is possible for objects of a specific size to be identified in the images being viewed and this can enable suspects for whom size information is known to be tracked. Alternatively to assist in identification of suspects of known size, all objects in the image having the same size

- 6 characteristics as the suspect can be identified by the control station 12.

Furthermore, if the surveillance system of the invention is utilised at sporting events additional information concerning the position, size and movement of athletes or players can also be derived using this system.

5 It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiments which are described by way of example only.

1. i..... À c e. c Àq À.'. À

Claims

- 7 CLAIMS

1. A surveillance system comprising at least one monitoring device operable to produce video images of a surveillance area, the at least one monitoring device being linked to a control station where said 5 video images can be viewed, said system further including an image processing means which acts to identify the relative position and relative size of known objects in said image for which a statistical distribution of size is known and which calculates a scaling factor therefrom, said scaling factor being calculated for each position of 10 known objects in said image whereby the scaling À factor can be applied to unknown objects in the said image to give an absolute indication of size.

2. A surveillance system as claimed in Claim 1, wherein the or each

monitoring device comprises a digital closed circuit television (CCTV) 1 5 camera.

3. A surveillance system as claimed in Claim 2, wherein said CCTV camera incorporates said image processing means.

4. A surveillance system as claimed in Claim 2, wherein said control station incorporates said image processing means.

20

5. A surveillance system as claimed in any preceding claim, wherein the control station comprises a computer.

6. A surveillance system as claimed in any preceding claim wherein the control station is remote from the or each monitoring device.

- 8

7. A surveillance system as claimed in any preceding claim, wherein the link between the or each monitoring device and the control station is a hardwired link.

8. A surveillance system as claimed in Claim 7, wherein the hardwired 5 link comprises electronic universal series bus (USB) cable.

9. A surveillance system as claimed in any one of Claims 1 to 6, wherein the link between the or each monitoring device on the control station is a wireless link.

to. A surveillance system as claimed in Claim 10, wherein the wireless

10 link is a microwave link.

11. A surveillance system as claimed in any preceding claim wherein the image processing means is operative to use a fixed object within the image of known size to calculate absolute size values of objects within the image.

15

12. A surveillance system as claimed in Claim 11, wherein the image processing means is operative to calculate the height of the monitoring device.

13. A surveillance system as claimed in Claim 11 or Claim 12, wherein the image processing means is operative to calculate the angle of 20 inclination of the monitoring device.

14. A surveillance system as claimed in any preceding claim wherein the image processing means is operative to identify objects of a specific size within the image.