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Welcome to our monthly news roundup for Businesses and Homeowners across Yorkshire and beyond.


This month:  Why CCTV ?  and “Getting the Image Size” right …

If you’re thinking “I need CCTV” the first and most important question to be addressed is “What do I need to see?” closely followed by “Why do I need to see it?”

CCTV which doesn’t meet your objectives is a waste of money. Careful consideration about what your system is to achieve is key. Your objective might be: prevention of theft, trespass, criminal damage, anti-social behaviour or many other crime-related activities. Maybe you need help with the management of staff, the public, vehicles, licensing compliance, financial and public transactions, and alarm verification. Health and safety may be important, including crowd management, life preservation, lone worker protection, staff-public interfaces, or access control to secure areas.

If CCTV is to meet your objectives try answering why, where, what, when, how and who.

Formally, this thinking process is detailed in the CCTV Operational Requirements Manual 2009, publication no. 28/09, by the Home Office Scientific Development Branch (since renamed CAST). This is a freely available 55-page downloadable PDF document.

One key consideration is Image Size. A suitable camera can only be recommended when we understand the nature of the activity to be observed. To simplify the situation we consider five general observation categories which are based on the relative size that a person appears on a screen.

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Monitor and Control: A figure occupies at least 5% of the screen height and the scene portrayed is not unduly cluttered. From this level of detail an observer should be able to monitor the number, direction and speed of movement of people across a wide area, providing their presence is known to him; i.e. they do not have to be searched for.

Detect: The figure now occupies at least 10% of the available screen height. After an alert an observer would be able to search the display screens and ascertain with a high degree of certainty whether or not a person is present.

Observe: A figure should occupy between 25% and 30% of the screen height. At this scale, some characteristic details of the individual, such as distinctive clothing, can be seen, whilst the view remains sufficiently wide to allow some activity surrounding an incident to be monitored.

Recognise: When the figure occupies at least 50% of screen height viewers can say with a high degree of certainty whether or not an individual shown is the same as someone they have seen before.

Identify: With the figure now occupying at least 100% of the screen height, picture quality and detail should be sufficient to enable the identity of an individual to be established beyond reasonable doubt.

The Monitor or Detect categories may be suitable for covering a wide area such as a car park. The Observe category is useful in areas where it is necessary to monitor a group of individuals such as outside nightclubs and pubs, or in town centres, as it provides reasonable detail of the subject whilst simultaneously providing some context to their activity by monitoring the area around them.

The Recognise or Identify categories would be used for the cameras providing close-up images at the entry and exit points. In scenarios where the purpose of the camera is primarily access control and identity verification, a figure much greater than the 100% Identify setting may be required.

The purpose of these categories is to suggest appropriate image sizes to aim towards when specifying a system to meet a particular requirement, rather than to define a minimum standard. It does not follow that it will be impossible to recognise or identify an individual if the image size is smaller than the 50% or 100% figures suggested. Equally, there is no guarantee that individuals will be identifiable just because they occupy >100% of the screen. Other factors, such as lighting and angle of view will also have an influence.

The situation is further complicated for the recorded imagery, as the recording picture quality may be different to the LiveView. Put simply, this means that a figure that occupies 50% of the screen height and can be recognised from the LiveView may not be recognisable in the recorded view, as the compression process or recording resolution has led to a loss in picture detail. For this reason it is vital to consider the recorded picture quality as well as the LiveView when installing a CCTV system.

As always, if you have any questions or comments please don’t hesitate to contact us …

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