Notions of motion

Video Motion Detection’s (VMD) basic raison d’être is to relieve the CCTV Control Room operator of the impossible task of attempting to continuously watch any number of monitors displaying images from an even larger number of cameras. For the most part, very little activity – if there’s any activity at all – will be taking place.

VMD, then, will pinpoint movement in a space and alert the camera operators accordingly. There are, of course, degrees of sophistication, ranging from a simple alert through to any change in the picture and on again to sophisticated intelligent systems which must differentiate the environment from moving targets. They must also provide a very high degree of accuracy as required by high specification security applications.

While the former can be provided by simple, low cost systems, the latter demand more careful thought and evaluation on the part of the security manager.

If reliable, VMD will free CCTV operators for numerous other security tasks in the certain knowledge that, when an alarm does occur, it will receive maximum attention. The value of operator confidence – in addition to operator stress – is an equal and opposite reaction. The net result is a much more effective surveillance system, and a more cost-effective system because there is now full use of the cameras on site and the realisation of effective operation.

VMD technology has come a long way in recent years, but in order for it to fulfil the concept design purpose, the secure zone area must be continuously monitored. If the cameras used are of the PTZ variety, what is monitoring the area when the camera is looking elsewhere? Now there’s a question... In reality, the mixture of VMD and PTZ cameras is somewhat contradictory.

All VMD set-ups use the same basic information – in short, the video signal from the CCTV camera. This is an electrical representation of the instantaneous grey shades in the picture. How this information is processed – and the design philosophy of the manufacturer – is where the (often substantial) differences occur between systems.

Light changes and processing speed

Light level fluctuations can realise massive changes in the video signal that are often seen by these systems as movement. This movement can (and will) result in false alarms. Fluctuations in the video signal caused by brightness changes are seen by the system whether they are initiated by an illumination or movement change. Remember that a small, moving man-sized target presents a much smaller change than, for example, the sun coming out from behind the clouds!

To detect changes in the image, the system has to be able to compare the current camera image with a previous one. A running man, passing close to – and across – the field of view of a camera would pass in a matter of tens of milliseconds. Due to the frequent use of only a single processor with a number of cameras, even the fastest processing/comparison rates used in some VMD systems aren’t really fast enough to ‘see’ this situation.

An often-overlooked factor is that CCTV is two-dimensional, and yet we are viewing a three-dimensional scene in a three-dimensional environment. This means that a target in the near field would be large but become progressively smaller further away from the camera. Becoming smaller, yes, but every bit as important nonetheless.

To take care of these ‘perspective effects’, as a minimum the VMD must have the ability to adjust the size and shape of the zones such that they correspond to the same size as the anticipated moving object, thereby taking perspective into account.

In any CCTV installation, outdoor cameras will more-than-likely experience a small amount of shake or movement in windy weather. Any VMD system used externally must have the ability to differentiate between motion in the field of view and motion emanating from the camera itself.

Evaluating a VMD system

Any Video Motion Detection system used externally must have the ability to differentiate between motion in the field of view and motion emanating from the camera itself

When seeing a system, and particularly for the first time, how does the end user begin to establish that it will perform – in theory, at least – to their requirements? All of the foregoing can be related to a very simple, practical five-point test as follows:

(1) The system is operating with a camera in the room... turn off the lights and observe the reaction of the sensor. Do this both slowly and quickly to establish system tolerance to both slow and fast illumination changes;

(2) Shake the camera gently to simulate wind-induced housing tremble, and observe zone movements to establish the tolerance levels in relation to camera movement;

(3) Introduce both slow and fast-moving targets for the sensor to detect (for example, a small ball of rolled-up paper thrown across the camera’s field of view);

(4) The ultimate test is now to introduce camera tremble and, simultaneously, introduce a small moving target. This represents the combination of a windy night and an intruder– in other words, the worst possible duo you could organise!

Does the system ‘see’ the camera movement or the intruder? Does it ignore the intruder because of the camera movement? Or does it perform as you would need by ignoring the camera movement but still respond to the intruder? This is the most difficult test for any system, but you must ask to see it because it’s only if the VMD can handle these problems that it would suffice for your installation.

(5) If you have reached this point you must now close your shortlist. Ensure that the system can detect a known target size both near to and far away from the camera by actual field trials. Your investment deserves nothing less!

The range at which a video sensor is effective is also something that needs careful investigation and close questioning of the solutions provider wishing to sell you their system. The ability for VMD systems to react properly to a man-size target at both 10 metres and, say, 70 or 80 metres and ignore small mammals – while at the same time resisting alarm conditions created by drastic changes in background illumination and/or wind-induced camera tremble – will soon flush out the knowledgeable!

With careful site planning, a very successful and worthwhile system is easily achievable – and the end user’s investment in VMD will be quickly justified.

Automatic Number Plate Recognition

Using a CCTV camera, an Automatic Number Plate Recognition (ANPR) system firstly locates the number plate on a given vehicle and then reads and interprets the plate. Usually, the system can create a log of vehicle movements with date, time and location.

Systems can not only read a plate but, having interpreted it, the software can usually look up the plate in a database and display information about the vehicle or driver on an operator’s screen. Instantaneous warnings may then be given for vehicles of interest.

ANPR is suited to both security and access control applications. Systems may be stand-alone (ie one computer in the Security Control Centre connected to one or two cameras). There is often a requirement to build expandable, fully-integrated ANPR systems spanning a wide geographical area. This is a specialist subject, and camera type and location is critical.

There is often a requirement to build expandable, fully-integrated ANPR systems spanning a wide geographical area. This is a specialist subject, and camera type and location is critical. System operation must be clearly defined and understood

System operation must be clearly defined and understood, and a recognised, professional ANPR company consulted as necessary. Applied sympathetically and under controlled conditions, ANPR can indeed be a powerful management tool.

Moveable cameras: the PTZ

For the benefit of those security practitioners who are not overly-familiar with PTZ cameras, they consist of custom-assembled combinations of CCTV cameras, a lens, housing, pan and tilt unit and (generally speaking) lighting units.

Various combinations of components are assembled to meet specific end user requirements concentrating on resolution, sensitivity, night-time capability, distance to target object/area, local lighting levels and the lens motorisation itself.

The combination of components should be carefully selected by the security installer for compatibility, and will be custom-built to meet the requirements and prevailing conditions.

There are benefits to PTZ cameras. For a start, they can be tailored to meet a variety of performance demands. Generally, their camera/lens combinations are more sensitive than for domes in low light conditions. This type of camera may also be fitted with wash/wiper devices for use at arduous locations such as roadsides. They can be installed within explosion-proof housings for use in petrochemical facilities, and also deployed in conjunction with infrared lighting.

However, security managers should bear in mind that PTZs do have their downsides, too. They are something in the region of two-to-three times the cost of equivalent dome cameras. It is also obvious to any would-be criminals which way they are pointing at any given time, and therefore what they are monitoring. It must be said, too, that this type of camera is relatively slow to react to positioning via pre-set.

Dome cameras, on the other hand, comprise a complete, factory-built camera, lens, pan and tilt and telemetry receiver assembled into a dome enclosure. Early versions used full size camera/lens combinations but, more commonly, the units now use small camcorder modules. The quality in terms of image resolution, sensitivity and mechanics has improved significantly over the past few years, rendering domes increasingly popular for applications in non-arduous conditions.

Turning to the domes

Like PTZs, there are pros and cons to dome cameras, too. On the plus side, they boast an unobtrusive appearance and are relatively inexpensive. The ‘smoked’ domes can also obscure miscreants from being able to see in which direction the lens is pointing.

However, domes cannot be used with co-located lighting, and the camera views through a polycarbonate dome are optically not quite as good as those through flat glass. Domes can also be prone to scratching during routine cleaning and maintenance, with camera performance restricted to a limited range of standard modules.

In practice, a moving camera can only look at one place at a time. If any particular view is critical to the site operation then a permanent, fixed camera should always be used in preference to one that moves.

For the most part, any kind of moving camera should be seen as a ‘response’ mechanism for the trained and skilled CCTV operator to deal with any incidents witnessed on fixed cameras.