Axis Communications 241SA - page 73

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AXIS 241QA/AXIS 241SA - Glossary
CCD (Charged Coupled Device) - This light-sensitive
image device used in many digital cameras is a large
integrated circuit that contains hundreds of thousands of
photo-sites (pixels) that convert light energy into
electronic signals. Its size is measured diagonally and can
be 1/4", 1/3", 1/2" or 2/3".
CCTV (Closed Circuit Television) - A CCTV system is a
closed/private video system, usually constructed with
coaxial cabling, and used within a single building/group
of buildings. It is used to visually monitor the location for
security or industrial purposes. Video from the CCTV
system can be recorded and viewed on-site or remotely.
CCTV video camera - A traditional CCTV video camera is
an analog camera, available in both monochrome (black
and white) and color. Cameras can be set in fixed
positions or placed on "Pan/Tilt/Zoom" devices, which
allow the camera to be maneuvered. Using a zoom lens
provides a closer view of the object being viewed. CCTV
analog video cameras can be viewed over a computer
network by using a video server.
CGI (Common Gateway Interface) - A specification for
communication between a web server and other (CGI)
programs. For example, a HTML page that contains a form
might use a CGI program to process the form data once it
is submitted.
CIF (Common Intermediate Format) - CIF refers to the
analog video resolutions 352x288 pixels (PAL) and
352x240 pixels (NTSC). See also Resolution.
Client-server - Client-server describes the relationship
between two computer programs in which one program,
the client, makes a service request from another program,
the server, which fulfils the request. Typically, multiple
client programs share the services of a common server
program. A web browser is a client program that requests
services (the sending of web pages or files) from a web
server.
CMOS (Complementary Metal Oxide Semiconductor) - A
CMOS is a widely used type of semiconductor that uses
both negative and positive circuits. Since only one of the
circuit types is on at any given time, CMOS chips require
less power than chips using just one type of transistor.
CMOS image sensors also allow processing circuits to be
included on the same chip, an advantage not possible
with CCD sensors, which are also much more expensive to
produce.
Coaxial cable - Coaxial cable is the standard means of
transmitting analog video in a CCTV system. Coaxial is
also used by cable companies to distribute television in
residential buildings.
Codec - In communications engineering, a codec is
usually a coder/decoder. Codecs are used in integrated
circuits or chips that convert e.g. analog video and audio
signals into a digital format for transmission. The codec
also converts received digital signals back into analog
format. A codec uses analog-to-digital conversion and
digital-to-analog conversion in the same chip.
Codec can also mean compression/decompression, in
which case it is generally taken to mean an algorithm or
computer program for reducing the size of large files and
programs.
Composite video - A type of video signal in which the
red, blue and green signals (sometimes audio signals too)
are mixed together.
Compression - See Image Compression.
Contrast - Defines the degree of difference between the
lightest and darkest parts of an image or video stream.
Control unit - If a CCTV system has more than one
camera, there must be a way to control the video signals
going to recorders and monitors. There are three basic
types of Video Control Unit: Multiplexer, Switch and
Quad.
dB (Decibels) - A unit to measure sound level changes. A
3dB change is the smallest level change we can hear. A
3dB change is actually twice or half the audio power
level. A gain of 0dB will leave the signal level unchanged.
DC-Iris - This special type of iris is electrically controlled
by the camera, to automatically regulate the amount of
light allowed to enter.
Decoder - See video decoder.
De-interlacing - See interlacing.
DHCP (Dynamic Host Configuration Protocol) - DHCP is
a protocol that lets network administrators automate and
centrally manage the assignment of Internet Protocol (IP)
addresses to network devices in a network.
DHCP uses the concept of a "lease" or amount of time that
a given IP address will be valid for a computer. The lease
time can vary, depending on how long a user is likely to
require the network connection at a particular location.
DHCP also supports static addresses for e.g. computers
running web servers, which need a permanent IP address.
DNS (Domain Name System) - DNS is used to locate and
translate Internet domain names into IP (Internet
Protocol) addresses. A domain name is a meaningful and
easy-to-remember name for an Internet address. For
example the domain name www.example.com is much
easier to remember than 192.0.34.166. The translation
tables for domain names are contained in Domain name
servers.
Domain server - Domains can also be used by
organizations that wish to centralize the management of
their (Windows) computers. Each user within a domain
has an account that usually allows them to log in to and
use any computer in the domain, although restrictions
may also apply. The domain server is the server that
authenticates the users on the network.