Video Surveillance Glossary of Terms [A]

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• » Access Card [top]
  Approximately the size of a credit card, these are specially coded cards given to employees and allow them access to secure locations or devices at work.  Access cards utilize several technologies such as magnetic strips, Barium Ferrite, proximity (active or passive), and other methods.  They are often ‘swiped’ and read by a device that allows the user or employee access.
  
• » Access Code [top]
  Similar to a password, this series of numbers or letters enables a user to access a system or computer.  At job sites an access code can be the system or process that oversees employees or cars both in and out of certain areas.
  
• » Access Point [top]
  These are specific entry points in certain secures areas.  A card reader and monitor switches allow authorized entry by individuals with access cards.
  
• » ActiveX [top]
  ActiveX is Microsoft software component technology, mainly used by Microsoft Windows.  They facilitate sharing of information between differing applications.  Digital video recorders utilize ActiveX to remotely view security cameras online.
  
• » Activity Detection [top]
  Mutliplexers use this feature, which is a video motion detection technique, to give relay closure for alarms and to improve the update times of video cameras. 
  
• » AGC (Automatic Gain Control) [top]
  AGC increases the signal strength of security cameras when the light level decreases, and puts a cap on it during higher levels; this keeps the output signal consistent. 
  
• » AI (Auto Iris) [top]
  A useful feature to have in a video camera, an auto iris compensates for variations in light levels, from sunlight to shadows.  Essentially, the auto iris opens and closes the lens iris as the light changes; this also prevents the camera from being damaged by very bright sunlight.
  
• » Alarm Input [top]
  When attached to a security camera, an alarm input provides enhanced security in the form of a sensor device, often a door contact or a Passive Infra-red detector for motion detection.  Alarm inputs can be self powered or can require external power (usually 12V). 
  
• » ALC (Automatic Level Control) [top]
  Some security cameras feature ALC, which means the camera can bring out detail in bright or dark areas of an image.  If too much sunlight makes an image too dark, ALC can focus on the needed image.
  
• » Algorithms [top]
  Its general definition means a set of mathematical instructions to solve a task.  In the field of video technology, they enable digital compression of the video picture.
  
• » Ambient Light Level [top]
  This is the amount of background light present at any specific time.
  
• » Analog Signal [top]
  Analog signals are produced by most security cameras.  Analog signals are continuously variable, and are greatly affected by ‘noise’ (disturbances) within the system, and recordings of analog information (such as videotapes) degrade over time.  This doesn’t occur with digital signals recorded on media like CDs, DVDs and computer hard drives.
  
• » Angle of view [top]
  Also known as viewing angle, this refers to the angular range available within a certain image size.  The smaller the focal length, the wider the angle of view is. 
  
• » Annunciator [top]
  This is a signaling device, either visual or audio based.  For example, wireless annunciators use infrared beams that trigger an audible signal when interrupted, and can be used for security or retail purposes. 
  
• » Aperture [top]
  An aperture is a lens opening that controls how much light reaches the film or digital sensor.  Iris adjustment controls aperture size, and a series of f-stop numbers dictate how much light passes through the lens.  A smaller aperture allows for better focus on objects outside the camera’s plane of focus.
  
• » ARP (Address Resolution Protocol) [top]
  ARP is a method determining a host’s Ethernet address from its Internet address.  The network receives the ARP request, and then names the IP address.  Next, the machine at this address returns its physical address so the information can be sent to it.  If supported by all hosts, Internet addresses can be independent of Ethernet addresses. 
  
• » Aspect Ratio [top]
  Aspect Ratio refers to the ratio between an image’s height and width. Differing mediums such as television, HDTV, and film, use different aspect ratios.  Within computer graphics, it refers to the shape of an individual pixel in a digital image. 
  
• » Attenuation [top]
  A reduction in light strength or electrical signal, usually because of absorption or scattering, is called attenuation.  The use of triaxial cables can minimize attenuation.
  
• » Automatic White Balance [top]
  Cameras with this feature installed will automatically adjust color settings to achieve consistent quality in the white areas of the image.
  
• » AVC (Advanced Video Coding) [top]
  Both the ITU and MPEG groups have agreed upon AVC as the current video compression standard.  ITU calls it H.264, the MPEG group refers to it as MPEG-4, and the public calls it AVC.

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