CCTV London - AMSSL

 

Prior to installing or enhancing any CCTV system a clear understanding should be obtained regarding what the system is required to do and how it should perform and operate.

To realise the maximum benefits of the CCTV systems it is strongly recommended that new installations should be developed with an open protocol technology to allow an interface with other pertinent systems, e.g. links between your own CCTV systems and those belonging to local authorities, etc.

It is recommended that from an early stage all 3^rd party organisations such as Local Authorities and other operators should be made aware of and involved as appropriate in any proposals to carry out CCTV systems installation or enhancement .

This will not only be helpful in securing their support for such schemes but will also serve to highlight any issues relating to the operation, management and monitoring of the system as well as helping to ensure that what is being proposed for the building, station and car park is considered in context with the surrounding area and the local environment.

In conjunction with the Local Community or Police Crime Reduction Officer an audit of crime and disorder at the location premises or area to gain an understanding of the safety and security issues in the local environment. It is important at this stage they identify the areas that will need CCTV surveillance. The audit will help to determine how many cameras are needed and what views are to be obtained (e.g. general views of the area, ability to recognise the face of someone walking through a doorway, or read a vehicle registration number).

When planning, consideration should be given to other security equipment that is going to interface with the CCTV system together with the location of the equipment. Equipment such as Acces Control Systems, Fire Alarms, Intruder Alarms, Help points, CCTV recorders (type and quantity), output interfaces to the outside world, interface equipment to other internal equipment.

CCTV Camera Lighting

Realising and understanding the relationship between the CCTV systems, lighting and the local geographical layout is of utmost importance in ensuring the highest quality pictures possible. CCTV systems and lighting should never be designed independently and insufficient lighting should not be compensated for by enhancing CCTV sensitivity. Insufficient or unevenly distributed lighting will have a significant impact on the operational performance and quality of images of the selected CCTV system.

Where possible the lighting used in conjunction with CCTV should be “white” lighting and be position above rather than below the area within the cameras field of view.

Maintaining a suitable light level over the scene being monitored is a big step to ensuring the system performs to its optimum performance.

A lighting survey is recommended before any CCTV camera installation to ensure scenes are sufficiently illuminated and the appropriate CCTV and lighting systems are installed to optimise performance.

When setting up cameras in daylight conditions a neutral density filter, which sits in front of the camera lens, can be used to simulate low light condition by opening the iris fully.

The appropriate British and European Union (EU) Standards should be used as guidance to lighting requirements when used in conjunction with the CCTV systems.

CCTV Cameras

There are many types of CCTV cameras on the market today that are more than capable of meeting the needs of any CCTV system required. It is therefore important a site survey is carried out to ensure the operational requirements are fully understood and defined. However, having clearly defined operational requirements of the CCTV system there are two main factors that need to be considered with respect to camera selection. Namely, the lens and the sensor element as together they will determine the CCTV camera’s capability including image resolution, field of view and its low light capability. With the introduction of IP and wireless technology consideration on how the camera transmits its images to the rest of the CCTV system.

A Pan Tilt & Zoom (PTZ) CCTV camera can be used as a tracking tool for remote monitoring applications, providing the operator with a 360 degree field of view and the ability to manually track and pin point a target. When tracking a target it is advantageous to record the images at their normal moving rate (Real Time Recording).

To ‘pan’ a camera is to rotate it horizontally; to ‘tilt’ a camera is to rotate it vertically; a ‘zoom’ lens allows the focal length to be adjusted.

The advantages of PTZ are:

The disadvantages of PTZ are:

• May not provide a useful field of view when not actively monitored
• Higher maintenance costs
• Privacy intrusion

It should not be expected that enhanced viewing features, such as zoom controls, will provide extra detail. In addition, it should be noted that the quality of the recorded or printed pictures may differ from the live display.

CCTV Viewing Screens

Key to the selection of a viewing screen for the CCTV system is cost, size of space to house the displays and how they are intended to be used. Generally there are 3 main types of viewing screens that can be selected: CRT, LCD and Plasma. (Newer LED and OLED TVs are becoming available) Whichever viewing screens are selected, consideration should be given to the ergonomics of the viewing facility it is to be housed in and the user and how they interface and use the equipment.

The CRT is capable of producing a better quality picture, is a proven technology and is relatively low cost. However, it has high power consumption, high heat generation and needs a greater space in which to locate it.

The LCD is compact and light, has low power consumption is relatively low cost and has a wide range of screen sizes. On the negative side it has poor movement reproduction, restricted viewing angles and low image contrast.

The Plasma unit is slim in design has a range of large screens and better viewing angles. It is however, fragile has high power consumption and tends to be expensive to purchase.

Also there is a fourth type of display, back screen projection. This however needs a great deal of space, is expensive, generates a great deal of heat and needs a lot of power.

CCTV Image Quality

Image quality is a very debatable and emotive subject. In the main, because it is an individual’s perception, it is very hard to quantify.

There are four areas to consider when looking at CCTV images being displayed.

Clarity – is the picture sharp enough and is there distortion.

Detail – is there enough to identify objects

Colour – is it natural

Artefacts – are there elements in the image that should not be there, are they obtrusive?

When using digital technology one of the key factors that impact on image quality is the compression rate of files that are being transferred from the cameras to the recorders or other output ports within the CCTV system. As a general rule the more compression applied to images the smaller the file size for saving but the greater the loss of image quality in terms of clarity, detail and colour.

A fundamental functionality of any CCTV system is its ability to transmit or move the recorded images from one place to another or from one recording/storage medium to another. The picture viewed on a monitor will invariably be of better quality than a recorded image and may even be displayed at a higher image rate.¹Therefore when assessing the quality of an image it is of vital importance to make the assessment from a previously recorded sequence and preferably from a sequence of images that have been exported to the type of storage device that will be passed to the police or other authorised user of the system. This is a critically important consideration when CCTV systems are being demonstrated prior to purchase.

Recorded Image quality can be measured using the following basic criteria:

• The previously agreed camera field of views, as specified at the design stage and in the operational user requirement form the benchmark for commissioning.
• The Home Office approved ‘Rotakin’ test target provides the measurable performance criteria.
• A suitable calibrated colour test card will determine the colour quality for static commissioning testing.
• Dynamic commissioning consists of recording moving objects to examine for signs of blur or picture lag.
• Suitable acceptance documentation listing the above criteria should be agreed in advance.

The definition of “image” when used in the context of IPSPC (Images per second per camera) is one complete image (or frame) of video i.e. when measuring interlaced video where a frame is actually made up of two interlaced fields - image refers to the complete frame (both fields combined).

CCTV System Validation

To ensure the CCTV system installed meets the operational user requirements established at the start of the project it is important that consideration is given to formal commissioning and acceptance of the CCTV system when ownership and system responsibility passes from the contractor to the station and/or station car park operator.

In addition, the operator should ensure all the correct documentation (operational manuals, maintenance manual, acceptance documents, etc.) are handed over and truly reflects the system installed.

Particular areas to check are

• Cameras Field of View
• Live and Recorded image quality
• Storage time provided by the system
• The operation of additional features
• Training and maintenance to be provided for staff

It is recommended the contractor supply an “audit” pack containing details of the installation, number of cameras, number of recorders and which camera is connected to which recorded. In addition, a still picture from each camera should be included in the audit pack. This can be used at a later date for reference as and when required by your staff or authorised stakeholders such as policing authorities.

All cameras should be individually commissioned with live image quality checked against both recorded and exported image quality using the Home Office approved ‘Rotakin’ test target and a suitable calibrated colour test card to determine colour quality. By specifying required screen height and resolution (indicated by the markings on the target), the camera/lens performance can be checked to confirm compliance with the system specification in accordance with HOSDB 55/06 “CCTV Operational Requirements Manual”. A human volunteer could act as a substitute should no Rotakin be available.

Once the live camera view has been checked, it is vital that the quality of the recorded images is also assessed to confirm that there has not been an unacceptable loss in detail during the recording process.

More CCTV Technical Information and Guidance