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Glossary of Terms

Glossary of Terms

D/A
Acronym for Digital to Analog.
D-channel
In an ISDN network the D-channel is a signaling channel over which the carrier passes packet-switched information. The D-channel can also support the transmission of low-speed data or telemetry sent by the subscriber.
D Connector
A connector with rounded corners and angles ends, taking on the shape of the letter "D". Commonly used in computers and video.
DA
Acronym for Distribution Amplifier.
DAC
Acronym for Digital to Analog Converter.
DAT
Acronym for Digital Audio Tape.
Data
(1) A representation of facts, concepts, or instructions in a formalized manner suitable for communication, interpretation, or processing by human or automatic means. (2) Any representations, such as characters or analog quantities, to which meaning is, or may be assigned.
Data Compatibility
Relates to the video and computer signal formats the projector is capable of displaying.
Data Compression
Reducing the size of a data file by reducing unnecessary information, such as blanks and repeating or redundant characters or patterns.
Data Monitor
A monitor with horizontal scan capability between 15.75 - 36 (42) kHz. Data monitors and projectors are commonly associated with NTSC video. IBM CGA through VGA and Apple/Macintosh computer input sources.
Data Rate
The rate or speed at which data is transmitted.
db
Acronym for Decibel.
dBA
Sound level measurement unit corrected for average human hearing response.
DBS
Acronym for Direct broadcast satellite.
DC
Acronym for Direct Current.
DC Coupling
A mode that passes both AC and DC signal components to the circuit.
DC Restoration
The correct blanking level for a video signal is zero volts. When a video signal is AC-coupled between stages, it loses its DC reference. A DC Restoration circuit clamps the blanking at a fixed level. If set properly, this level is zero volts.
DDC
Acronym for Display Data Channel.
Debug
To locate and correct any errors in a multimedia program.
Decibel
The standard unit used to express gain or loss of power. It indicates the logarithmic ratio of output power divided by input power. A power loss of 3 dB is an attenuation of half of the original value. The term "3dB down" is used to describe the "half power point".
Decoder
A device used to separate the RGBS (Red, Green, Blue and Sync) signals from a composite video signal (90 IQ).
  1. A television set-top device, which enables the home subscriber to convert an electronically scrambled television, picture into a viewable signal. This should not be confused with a digital coder/decoder known as a CODEC, which is used in conjunction with digital transmissions.
  2. A device that converts composite video to separate Red, Green and Blue Video. Doing this eliminates chroma "crawl" that is associated with NTSC video because RGB are combined on one channel. Manufacturers of video decoders include Extron, Faroudja and Snell and Wilcox.
Delay
The time it takes for a signal to go from the sending station through the videoconference to the receiving station. This transmission delay for a single hop videoconference connection is very close on one-quarter of a second.
Delivery System
The computer and media hardware components used to deliver a multimedia or interactive video program. Delivery systems range from a videodisc player with an on-board microprocessor, a monitor and a keypad to a personal computer, more than one monitor and a variety of peripheral devices such as a mouse, printer, a CD-ROM, and so on.
Demodulator
A device which operates on a carrier wave to recover the wave with which the carrier was originally modulated.
Depth Of Focus
A measure of an imaging system to keep an image in focus when the object plane is NOT thin.
Desktop Publishing
The use of a personal computer as a production system for generating typeset-quality text and graphics.
Device Driver
Software that allows the computer to communicate with a peripheral device, such as a printer, a videodisc player, and/or a CD-ROM player.
Differential Audio
See Balanced Audio.
Differential Gain
Variation in the gain of the chrominance signal as the luminance signal on which it rides is varied from blanking to white level.
Differential Phase
Variation in the phase of the chrominance subcarrier as the luminance signal on which it rides is varied from blanking to white level.
Digital
A method in which signals are represented by a set of discrete numerical values as opposed to continuously fluctuating current or voltage.
Digital Audio Tape
A method of recording digital audio information on tape at a high density and high quality. The method uses a rotating head, similar to that used in video tape recording.
Digital Satellite System
A digital DBS system developed by Hughes and Thompson and first marketed by RCA; the DSS initials are no longer used, and the system is now known as the DirecTVSatellite System.
Digital Signal
Digital signals have two levels, high/low or on/off. AKA;TTL.
Digital Television
fDigital Television. In general, a broadcast TV system in which
Digital-to-Analog Converter
A computing device that changes digital quantities into into a voltage or current whose magnitude is proportional to the numeric value of the digital signal.
Digital Video
Video where all the instructions for the images are in computer data form, i.e., bits. A method in which signals are represented by a set of discrete numerical values, as opposed to continuously fluctuating current or voltage.
Digitization
The transformation of an analog signal into digital information.
Digitize
To convert analog information into digital information, to record a visual image or real object in a format that can be processed by a computer.
Digitizers
Video digitizers utilize video cameras to take pictures of photographs or live and still action. The information is decoded into RIB (digital form) and stored in the frame buffet.
Dimensions
The physical size, length, width, and height of an InFocus projector, as measured in inches.
DIP
Acronym for Dual In-Line Package.
DIP Switches
Tiny switches that are used to change settings on printers, computers, interfaces, switchers, modems, etc. They are designed to fit in a DIP space on a circuit board.
Direct broadcast satellite
A system in which signals from a satelliteare received by home viewers directly, as opposed to systems that distribute signals only to cable-TV "head ends," which then distribute them to their customers. DBS can apply to satellite-distributed pager signals as well as to audio and video.
Direct Current
A signal with a constant voltage and current.
Disk Drive
A storage unit (devloped by Xerox) used by a computer made up of disks with a magnetic coating.
Disk Operating System
A computer operating environment designed to use a disk. Languages, applications and utility programs can be transmitted quickly between the disk storage system and CPU memory. DOS stands for both the Microsoft Disk Operating System (MS-DOS) and IBM's Personal Computer Disk Operating System (PC-DOS).
Display
A screen that electronically presents characters, numbers, graphics or other information transmitted from the personal computer. To show text and graphics on a monitor.
Display Color
There are two primary concerns which are related to color temperature: 1)The color temperature of the lamps and fixtures in the display environment - which we now understand, and 2)The color temperature of the display device itself. Adding certain amounts of a specific color of red, green and blue together creates television images. In order to reproduce the subtle nuances of the image, these quantities and colors need to be duplicated. Therefore, the red, green, and blue light that the display makes, should be as close as possible to the reference set forth by the television standards. The white point of the display (or the starting point at which we produce color) must be set to the white point of the signal (also set forth by the television standards). The white point is the color produced when equal amounts of red, green, and blue signals are applied. If this is not set properly, the image will be "colored" or skewed by the difference in the signal's white point, and the display's white point. Different television standards, and computer displays, all have a different area within this color space that they can display. This also means that, as depicted in the CIE chart, display devices can be set to different color temperatures. In the display world, bluer whites look cleaner and better than yellow whites. So while bluer whites may not be as accurate, many display devices are set to a bluer color temperature so that they can create more pleasing pictures. Other displays are set to more accurately render color. What has emerged are four color temperature standards for display devices.
The following are the established color temperature standards for display:
  • Computer standard (IEEE): 5400K
  • Film: 5400K. 5400K displays a subjectively better image and is warmer. It is also more accurate, but less bright than the 9300K. Computer monitors are now being shipped at 5400K, and the HDTV standards groups established it for its reference.
  • Video (SMPTE): 6500K. 6500K was selected because it produced colors reasonably accurately.
  • Consumer TV: Moved from 9300 to 12,000K (bluish). Blue draws the eye, and we perceive the image as crisper, sharper, and brighter.
Each color temperature standard produces color differently, making it virtually impossible to exactly match displays of different color temperature standards. The color temperature of a display device is determined by both user adjustments, and the phosphors used on the face of the CRT. The phosphor chromaticity produced by screen phosphors is strictly controlled, enabling different monitors to produce colors in the same way. The two most common standards for phosphors are the SMPTE D65 (6500 degrees Kelvin) used on professional video monitors, and the P22 standard used on consumer televisions, and most presentation displays. The SMPTE D65 standard for color temperature is very close to the average daylight color temperature. The P22 standard has a color temperature of 9300 degrees Kelvin that reproduces bluer colors. P22 was chosen because these phosphors are capable of greater output, producing brighter, more vibrant, pictures in adverse lighting conditions.
Display Technology
The type of technology used to produce bright, clear images in high resolution. InFocus projectors use many different display technologies such as Digital Light Processing and Liquid Crystal Displays (LCDs) combined with high-brightness lamps and precision optics.
Dissolve
Gradual fading of one image into another, done by changing the brightness of two superimposed projectors.
Distance Learning
The incorporation of video and audio technologies into the educational process so that students can attend classes and training sessions in a location distant from that where the course is being presented. Distance learning systems are usually interactive and are becoming a highly-valuable tool in the delivery of training and education to widely-dispersed students in remote locations or in instances where the instructor cannot travel to the student's site. Manufacturers of Distance Learning systems include: AMX, Crestron, PictureTel, V-Tel and Tandberg.
Distortion (Audio)
A modification of the original signal appearing the output of audio equipment that had not been present in the input. The most common way of expressing distortion is in percent of the original signal as Total Harmonic Distortion (THD).
Distortion (Geometric)
Pin cushion vs Barrel & Keystoning. A measure of how well a rectangular object gets projected without getting the shape changed.
Distribution Amplifier
A device that allows connection of one input source to multiple output sources such as monitors or projectors.
Dithering
Refers to the technique of mixing up either nearby neighboring imagesels (spatial) or consecutive frames (frame) of imagesel information in a random fashion to create the effect of many intermediate levels between what can be directly driven. This is the common way in which thousands (even millions) of colors can be projected.
DLP
Acronym for Digital Light Processing; a data projection technology developed by Texas Instruments using a microprocessor to display bright, colorful images in fully lit rooms. Used primarily in portable and ultra-portable projectors, the DLP chip is the size of a postage stamp and contains millions of microscopic mirrors one for each imagesel that flip on an axis, reflecting light through a color wheel to create your image.
DLP (Digital Light Processing )
See DMD.
DMD (Digital Micromirror Device)
In 1977, it was originally called "Deformable Mirrors Device". Texas Instruments has developed DMD microchips used in DLP (Digital Light Processing) projector subsystems that hope to replace the 100-year old CRT technology. DMD chips use an array of mirrors and memory cells. A digital image is stored in the memory and then projected when light is reflected onto the mirrors.
Domain Name System (DNS)
Network Service to resolve network nodes to IP addresses.
DOS
Acronym for Disk Operating System.
Dot Clock
(also imagesel Clock) The highest rate that a graphics device can produce.
Dot Pitch
The distance between the sets holes or slots (Trinitron system) for the colors on the adjacent line of a CRT monitor shadow mask. A smaller the dot pitch allows for more potential dots to be displayed, thus achieving better resolution (see Shadow Mask).
Double-Supertwist-Nematic LCD
An system of two STN LCDs stacked together.
Doubler
See Line Doubler.
DPT
Acronym for Desktop Publishing.
DRAM
Acronym for Dynamic Read Only Memory
DRAW
Acronym for Direct read after write. Type of optical disks that can be written to but not erased.
DSS
Acronym for Digital Sattelite System
DSTN
Acronym for Double-Supertwist-Nematic LCD.
DTL
Acronym for Diode Transistor Logic.
DTV
Acronym for Digital Television.
Dtv/HDTV 1280 x 720P (imagesels) progressive standard (externally transcoded to 1920 x 1080i
640 lines)
Dtv/HDTV 1920 x 1080i (imagesels) interlaced standard
960 lines
Dual In-Line Package
A universal method of manufacturing integrated circuits (ICs) with the pins arranged in two parallel rows. Dome DIP components are soldered in and some use DIP sockets.
Duty Cycle
The duration of any specific signal contained by a multiplexed signal. Often described as a percentage, e.g., in an equally weighted multiplexing scheme of 100 signals into one, the duty cycle would be 1%, meaning a given imagesel is being driven electrically 1% of the time. The relationship between multiplexing and duty cycle is inversely proportional - for slow multiplexing rates the duty cycle is high and for fast rates, the duty cycle is low. See also "Multiplexing".
DVD
(Digital Video Disc or Digital Versatile Disc) An optical disc system about the size of a CD ROM, but capable of storing an entire movie. The technology uses MPEG-2 compression. Typical capacity for these discs is 4.5 GB, or about 133 minutes of digital video.
DVI
Acronym for Digital Video Interactive. A technology from Intel Corporation that displays digital graphics and full-motion video along with real-time compression and decompression. On a CD-ROM, it provides up to 72 minutes of full-screen video, 2 1/2 hours of half-screen video, 40,000 medium resolution, or 7,000 high-resolution images. DVI can compress full-motion video at rates greater than 100 to 1 and still images at 10 to 1.
DVP
Digital Video Processing.
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