GB2325106A - Method of operating a surveillance system - Google Patents

Abstract

A surveillance system has a plurality of video cameras. Using a keyboard 12, the user selects a desired camera, and displays its output on the relevant monitor for a desired length of time (dwell time). Once the desired dwell time has elapsed, the next camera is selected, and so on. When any camera is selected, a controller automatically records the identity of the camera, and reads a system clock to commence the measurement of the intended dwell time for the camera. When the next camera is selected, the clock is read again and the difference between the two time readings is recorded, associated with the relevant camera identity, as the selected dwell time. This process is repeated until the desired sequence list has been created. The list is stored in a RAM 18 and controls the automatic selection of the cameras in use.

Description

METHOD OF OPERATING A SURVEILLANCE SYSTEM BACKGROUND OF THE INVENTION THIS invention relates to a method of operating a surveillance system comprising a plurality of video cameras.

Surveillance systems comprising a plurality of video cameras and associated monitors are widely used. The video cameras and monitors are controlled by a central controller, typically either a matrix switcher which can route any camera to any monitor(s), or a multiplexer which can display multiple cameras on one monitor and also send the information from several cameras to a single video recorder by using time division multiplexing (TDM). In either case, the central controller is typically built around a microprocessorbased central processing unit (CPU).

It is desirable for a user of the surveillance system to be able to select the sequence in which the output of different cameras is fed to a particular monitor, and for how long. This is conventionally done using a programmable "sequence list" which allows the user to specify for each monitor a camera list to sequence through, as well as a time period or "dwell time" for which each camera is selected. Such systems are somewhat clumsy and inconvenient to use, and it may require several attempts at setting up the sequence list before the desired result is obtained.

It is an object of the invention to provide a method of operating a surveillance system of the above kind which is easier and quicker to use than existing systems.

SUMMARY OF THE INVENTION According to the invention there is provided a method of operating a surveillance system comprising a plurality of video cameras and at least one monitor, the method comprising: (a) selecting a desired camera so that its output is displayed on the monitor; (b) automatically recording the identity of the selected camera; (c) waiting for a desired period, corresponding to an intended dwell time for the selected camera; (d) selecting a next desired camera and automatically recording the dwell time of the previous camera in association with its identity; (e) repeating steps (a) to (d) a desired number of times; and (f) operating the surveillance system by automatically selecting the respective cameras in accordance with the recorded identities and associated dwell times.

The method may include monitoring a time signal and recording the time period between the selection of a first camera and the selection of a subsequent camera as a dwell time for the first camera.

Preferably, the method includes monitoring a system clock, reading a first time value from the system clock when the first camera is selected, reading a second time value from the system clock when the subsequent camera is selected, and recording the difference between the first and second time values as the dwell time for the first cameras Further according to the invention there is provided a controller for a surveillance system having a plurality of video cameras and at least one monitor, the controller comprising: selection means operable by a user of the controller to select desired ones of the cameras one after the other; switching means responsive to the selection means for routing an output of each selected camera to the monitor; timing means; recording means for automatically recording data corresponding to the identity of each selected camera and a dwell time for which the respective camera is selected; and control means responsive to the recorded data to automatically select the respective cameras in accordance with the recorded identities and associated dwell times.

The recording means preferably comprises a processor arranged to monitor a time output signal of the timing means and to record the time period between the selection of a first camera and the selection of a subsequent camera as a dwell time for the first camera The recording means may further comprise a random access memory (RAM) for storing a sequence list comprising data identifying respective cameras and an associated dwell time data.

In the above definitions, the phrase "dwell time" is intended to mean the period of time for which each camera is selected.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic block diagram of a multiplexer-type control system for a multi-camera surveillance system; and Figure 2 is a simplified flow diagram illustrating the operation of software used to implement the method of the invention.

DESCRIPTION OF AN EMBODIMENT The block diagram of Figure 1 shows a multiplexer-type control system which controls the operation of 16 video cameras and selects their outputs for display on main and secondary video monitors as well as providing an output for a video cassette recorder (VCR). The system comprises a microprocessor based main controller 10 which is operated via a keyboard or keypad 12 and which includes an input/output interface 14, a read only memory (ROM) 16 which stores the operating software of the system, a random access memory (RAM) 18 which stores user-generated data, and the microprocessor 20 itself. The controller includes an RS232 port 22 for communication with peripherals.

The outputs of the respective cameras 1 to 16 are fed by a signal conditioning circuit to three multiplexers AMUX-l to 3. These multiplexers are controlled by the controller 10.

The first multiplexer AMUX- 1 selects a camera output which is digitized and formatted into one of several possible multi-image displays or a flill screen display, and is then fed to the main monitor. The second multiplexer AMUX-2 selects a camera output for the VCR output of the control system.

The third multiplexer AMUX-3 selects a full-screen camera output for the second monitor.

It should be appreciated that the invention is not limited to application with the above described hardware, in which multiple video outputs can be displayed simultaneously on a single monitor screen, and could be applied to a simpler matrix-type controller or a less complex multiplexer-type controller.

To program the operation of the surveillance system of Figure 1, a user is not required to prepare a menu-type sequence list as is done in prior art systems. Instead, the user simply selects each desired camera in turn, using the keyboard 12, and displays its output on the relevant monitor for a desired length of time, corresponding to the intended dwell time for that camera.

Once the desired dwell time has elapsed, the next camera is selected, and so on. When any camera is selected, the controller automatically records the identity of the camera, and reads the system clock to commence the measurement of the intended dwell time for the camera. When the next camera is selected, the clock is read again and the difference between the two time readings is recorded, associated with the relevant camera identity, as the selected dwell time. This process is repeated until the desired sequence list has been created. The list is stored in the RAM 18 and controls the automatic selection of the cameras in use.

By using the above method, a user is not required to know the identification code for each camera for entry into the sequence list, but can select cameras according to their output signal as viewed on the monitor. Similarly, it is not necessary for the user to estimate a length of time (typically in seconds) corresponding to the intended dwell time of a particular camera, which may have unpredictable results. Instead, the user simply retains the display of the output of the selected camera for a length of time which appears correct, before moving onto the next camera. In both cases, the identity of the camera and the intended dwell time are then recorded automatically. This results in a much more intuitive and user-friendly method of operation than prior systems. The flow chart of Figure 2 summarises the above procedure in graphic form.

The method of the invention is quicker to use than conventional systems, where the setting up of sequence lists is relatively time consuming. In conventional systems, the user typically cannot access the output of the various cameras while in the menu, and must therefore remember which camera number corresponds to which "scene" or camera output. This makes the procedure cumbersome and prone to errors. Typically, the user of a conventional system will have to prepare a rough version of the desired sequence list on paper before commencing the actual programming of the sequence list.

Also, in conventional systems a user does not see the effect of the programming until after the menu programming is ended and the sequence list is tested. In such a situation, a user may discover, say, that 3 seconds is not quite a long enough dwell period, or that 10 seconds is longer than expected.

The present invention makes it easy to vary the dwell time for each camera, whereas conventional systems often do not provide for variation of the dwell time on a camera by camera basis, due to the laborious nature of entering this information.

Claims (8)

CLAIMS:

1. A method of operating a surveillance system comprising a plurality of video cameras and at least one monitor, the method comprising: (a) selecting a desired camera so that its output is displayed on the monitor; (b) automatically recording the identity of the selected camera; (c) waiting for a desired period, corresponding to an intended dwell time for the selected camera; (d) selecting a next desired camera and automatically recording the dwell time of the previous camera in association with its identity; (e) repeating steps (a) to (d) a desired number of times; and (f) operating the surveillance system by automatically selecting the respective cameras in accordance with the recorded identities and associated dwell times.

2. A method according to claim 1 including monitoring a time signal and recording the time period between the selection of a first camera and the selection of a subsequent camera as a dwell time for the first camera.

3. A method according to claim 2 including monitoring a system clock, reading a first time value from the system clock when the first camera is selected, reading a second time value from the system clock when the subsequent camera is selected, and recording the difference between the first and second time values as the dwell time for the first camera.

4. A controller for a surveillance system having a plurality of video cameras and at least one monitor, the controller comprising: selection means operable by a user of the controller to select desired ones of the camera one after the other; switching means responsive to the selection means for routing an output of each selected camera to the monitor; timing means; recording means for automatically recording data corresponding to the identity of each selected camera and a dwell time for which the respective camera is selected; and control means responsive to the recorded data to automatically select the respective cameras in accordance with the recorded identities and associated dwell times.

5. A controller according to claim 4 wherein the recording means comprises a processor arranged to monitor a time output signal of the timing means and to record the time period between the selection of a first camera and the selection of a subsequent camera as a dwell time for the first camera.

6. A controller according to claim 5 wherein the recording means further comprises a random access memory (RAM) for storing a sequence list comprising data identifying respective cameras and an associated dwell time data.

7. A method of operating a surveillance system substantially as herein described and illustrated.

8. A controller for a surveillance system substantially as herein described and illustrated.