Sun Surveillance, wireless solar powered video surveillance, glossary d

The Glossary

An all inclusive glossary of security lingo is provided for your convenience. This list
will undoubtedly be helpful when delving in to the realm of security.

D:

D/A (also DA) - Opposite to A/D, i.e., digital to analog conversion.
Dark current - Leakage signal from a CCD sensor in the absence of incident light.
Dark noise - Noise caused by the random (quantum) nature of the dark current.
DAT (digital audio tape) - A system developed initially for recording and playback of digitized audio signals,
maintaining signal quality equal to that of a CD. Recent developments in hardware and software might
lead to a similar inexpensive system for video archiving, recording and playback.
DB - Decibel. A logarithmic ratio of two signals or values usually refers to power, but also voltage and
current. When power is calculated the logarithm is multiplied by 10, while for current and voltage by 20.
DBS - Direct broadcast satellite. Broadcasting from a satellite directly to a consumer user, usually using a
small aperture antenna.
DC - Direct current. Current that flows in only one direction, as opposed to AC. DCT - Discrete cosine
transform. Mathematical algorithm used to generate frequency representations of a block of video pixels.
The DCT is an invertible, discrete orthogonal transformation between time and frequency domain. It can be
either forward discrete cosine transforms (FDCT) or inverse discrete cosine transforms (IDCT).
Decoder - A device used to recover the component signals from a composite (encoded) source.
Degauss - To demagnetize.
Delay line - An artificial or real transmission line or equivalent device designed to delay a wave or signal for
a specific length of time.
Demodulator - A device that strips the video and audio signals from the carrier frequency.
Depth of field - The area in front of and behind the object in focus that appears sharp on the screen. The
depth of field increases with the decrease of the focal length, i.e., the shorter the focal length the wider the
depth of field. The depth of field is always wider behind the objects in focus.
Dielectric - An insulating (nonconductive) material.
Differential gain - A change in sub-carrier amplitude of a video signal caused by a change in luminance
level of the signal. The resulting TV picture will show a change in color saturation caused by a
simultaneous change in picture brightness.
Differential phase - A change in the sub-carrier phase of a video signal caused by a change in the
luminance level of the signal. The hue of colors in a scene change with the brightness of the scene.
Digital disc recorder - A system that allows recording of video images on a digital disc. Digital signal - An
electronic signal where every different value from the real-life excitation (sound, light) has a different value
of binary combinations (words) that represent the analog signal.
DIN - Deutsche Industrie-Normen. Germany’s standard.
Disk - A flat circular plate, coated with a magnetic material, on which data may be stored by selective
magnetization of portions of the surface. May be a flexible, floppy disc or rigid hard disk. It could also be a
plastic compact disc (CD) or digital video disc (DVD).
Distortion - Non-proportional representation of an original.
DMD - Digital micro-mirror device. A new video projection technology that uses chips with a large number of
miniature mirrors, whose projection angle can be controlled with digital precision.
DOS - Disk operating system. A software package that makes a computer work with its hardware devices
such as hard drive, floppy drive, screen, keyboard, etc.
Dot pitch - The distance in millimeters between individual dots on a monitor screen. The smaller the dot
pitch the better, since it allows for more dots to be displayed and better resolution. The dot pitch defines the
resolution of a monitor. A high-resolution CCTV or computer monitor would have a dot pitch of less than 0.3
mm.
Drop-frame Time Code - SMPTE time code format that continuously counts 30 frames per second, but
drops two frames from the count every minute except for every tenth minute (drops 108 frames every hour)
to maintain synchronization of time code with clock time. This is necessary because the actual frame rate
of NTSC video is 29.94 frames per second rather than an even 30 frames.
DSP - Digital signal processing. It usually refers to the electronic circuit section of a device capable of
processing digital signals.
Dubbing - Transcribing from one recording medium to another.
Duplex - A communication system that carries information in both directions is called a duplex system. In
CCTV, duplex is often used to describe the type of multiplexer that can perform two functions
simultaneously, recording in multiplex mode and playback in multiplex mode. It can also refer to duplex
communication between a matrix switcher and a PTZ site driver, for example.
DV-Mini - Mini digital video. A new format for audio and video recording on small camcorders, adopted by
the majority of camcorder manufacturers. Video and sound are recorded in a digital format on a small
cassette (66×48×12 mm), superseding S-VHS and Hi 8 quality.
D-VHS - A new standard proposed by JVC for recording digital signals on a VHS video recorder.
Dynamic range - The difference between the smallest amount and the largest amount that a system can
represent.

Courtesy of CCTV Labs and CCTV focus magazine

Glossary