Security

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• What is Lux?

  Lux is a measurement of light. To gauge the sensitivity of a camera we try to quote what level of light is needed to produce a video signal which is more than just a faint shadow and a screen full of snow.

  Therefore the lower the lux rating, the higher the sensitivity and the better the image will be in low light levels.

  Here are some typical estimates of lux levels:-

  • Bright sunny day: 10,000-100,000 Lux
  • Overcast day: 1,000-10,000 Lux
  • Twilight: 1-100 Lux
  • Street Lighting: 5 Lux
  • Full moon: 0.1 Lux
  • Bright clear starlight: 0.01-0.0001 Lux
  ­

  However, these indications are generally measured at the scene; i.e. someone stood under a street light with a lux meter and measured 5 lux. Unfortunately a CCTV camera is not usually under the street light – it is some way away looking at what is under the street light and therefore looking at reflected light.

  Imagine how much light is bounced back from the person under the street light in a dark jumper and jeans, probably only 5-10% which now means our 5 lux is reduced to a paltry 0.25 lux which may well produce an image on a camera with a sensitivity of 0.1 lux but we are very close to its working limit and this will show in the quality, clarity and detail of that picture.

  ­© Merit Lilin 2008

• What is Back Light Compensation?

  ­Back Light Compensation (BLC) digitally compensates for high-lights to enable silhouetted scenes to give more detail.

  When a camera is positioned looking at the entrance of a large glass fronted shop for example, the person walking in will often be silhouetted especially when the external light is high, as on a normal sunny day.

  The bright light will force the automatic iris to close. The camera can compensate to some degree for the difference between the ambient lighting and the light falling upon the target to be observed. However wherever possible use the ambient lighting to assist the camera technology.

  ©Merit Lilin 2008

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• What is the Difference Between IP and Analogue?

  Analogue CCTV systems use technology developed over 50 years ago, based on standard TV broadcasting technologies. Images are recorded in 'half-frames' to reduce bandwidth, which are combined or 'interlaced' when displayed. This can cause low resolution and blurring.

  IP camera systems use modern digital camera technology, resulting in a much larger and clearer picture. This does result in higher bandwidth and storage requirements.

   A good analogy would be to compare standard TV with HDTV.
  

  Feature	Analogue	IP
  Image Quality	Low	High
  Video Quality	Low	High
  Cabling System	Coaxial	Ethernet
  Scalability	Low	High
  Storage Requirements	Low	High
  Remote Access	No	Yes

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• What is Digital Storage?

  Digital storage is a means by which data in the form of text, images or voice is stored on a magnetic disk for retrieval at a later date.­

• What is a DVR?

  ­DVR stands for Digital Video Recorder. A DVR stores images from analogue CCTV cameras in a digital format on a hard disk unit. DVRs have replaced VHS based tape systems in the majority of CCTV installations over the last five years. Some manufacturers have designed DVRs to not only connect analogue cameras but also IP cameras concurrently e.g. Wavestore Crystal­ DVR.

• What is a NAS Box?
  ­

  ­A NAS 'box' (Networked Attached Storage) is a digital storage device that extends storage capacity on the LAN instead of installing larger disks inside existing network servers. A typical commercial NAS 'box' will have a 1 or 2 Terabyte hard disk capacity, although this can be scaled to suit any application. An Ethernet port (10/100/1000-T) and run Linux as the operating system. For users on the network it looks like an additional drive available (S:shared_drive) for storing shared documents/images etc...

  Depending on the software employed, a NAS 'box'­ can be a very cost effective method of storing images from IP cameras.

• What is an NVR?

  NVR stands for Network Video Recorder. ­An NVR­ is specifically designed to store images from IP based cameras via a single Ethernet port (10/100/1000-T). It usually runs a version of Linux and has installed as part of the system a software application for managing the attached cameras.

• Why do so many storage devices run on Linux?

  ­Linux is open-source operating system, based on Unix, which is regarded as more secure and offers higher performance than Microsoft Windows. Being open-source, it doesn't incur additional costs associated with licenses for the number of devices attached.

  As an example, to install a network of 40 IP cameras, an end user running a Windows system would require a Windows 2003 server license plus a license for each IP camera attached. With a Linux NAS server there are no licenses required.

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• What is Access Control?

  ­Access Control basically allows access to a secure location for a group of registered users. These registered users may gain access to the secure location via a variety of methods e.g. Keys, Swipe Cards (plastic cards with magnetic stripe), Keyfobs, Keypads and combinations of Voice/Fingerprint/Iris recognition. Another term used to describe such a system is '­Door Entry Control.'

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