User Guide

52
AXIS Q1755/-E - Glossary of Terms
Glossary of Terms
ActiveX - A standard that enables software components to
interact with one another in a networked environment,
regardless of the language(s) used to create them. web
browsers may come into contact with ActiveX controls, ActiveX
documents, and ActiveX scripts. ActiveX controls are often
downloaded and installed automatically as required.
Angle - The field of view, relative to a standard lens in a 35mm
st
ill camera, expressed in degrees, e.g. 30°. For practical
purposes, this is the area that a lens can cover, where the angle
of view is determined by the focal length of the lens. A
wide-angle lens has a short focal length and covers a wider
angle of view than standard or telephoto lenses, which have
longer focal lengths.
ARP (Address Resolution Protocol) - This protocol is used to
associat
e an IP address to a hardware MAC address. A request
is broadcast on the local network to discover the MAC address
for an IP address.
ARTPEC (Axis Real Time Picture Encoder) - This chip is used
for im
age compression.
ASIC (Application Specific Integrated Circuit) - A circuit
des
igned for a specific application, as opposed to a general
purpose circuit, such as a microprocessor.
Aspect ratio - A ratio of width to height in images. A common
aspect
ratio used for television screens and computer monitors
is 4:3. High-definition television (HDTV) uses an aspect ratio of
9:16.
Autoiris (DC-Iris) - This special type of iris is electrically
co
ntrolled by the camera, to automatically regulate the amount
of light allowed to enter.
Bitmap - A bitmap is a data file representi
ng a rectangular grid
of pixels. It defines a display space and color for each pixel (or
‘bit’) in the display space. This type of image is known as a
‘raster graphic.’ GIFs and JPEGs are examples of image file types
that contain bitmaps.
Because a bitmap uses this fixed raste
r method, it cannot easily
be rescaled without losing definition. Conversely, a vector
graphic image uses geometrical shapes to represent the image,
and can thus be quickly rescaled.
Bit rate - The bit rate (in kbit/s or Mbit/s) is often referred to
as speed,
but actually defines the number of bits/time unit and
not distance/time unit.
Bonjour - Also known as zero-configuration networking,
Bonjo
ur enables devices to automatically discover each other
on a network, without having to enter IP addresses or configure
DNS servers. Bonjour is a trademark of Apple Computer, Inc.
Broadband - In network engineering t
erms, this describes
transmission methods where two or more signals share the
same carrier. In more popular terminology, broadband is taken
to mean high-speed data transmission.
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".
CGI (Common Gateway Interface) - A specification for
communicat
ion 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 res
olutions 352x288 pixels (PAL) and 352x240 pixels
(NTSC). See also
Resolution .
Client/Server - Client/server describes the relationship
bet
ween 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 O
xide 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.
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/decompres
sion, in which
case it is generally taken to mean an algorithm or computer
program for reducing the size of large files and programs.
Compression - See
Image compression .
CVBS - analog video format (composite video).
DC-Iris (Autoiris) - This special type of iris is electrically
co
ntrolled by the camera, to automatically regulate the amount
of light allowed to enter.
DHCP (Dynamic Host Config
uration 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
t
ranslate 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