VECTORSCOPE
VERTICAL INTERVAL SWITCHING (VIS)
VERTICAL TILT
VGA (Video Graphics Array)
VHS
VHS-C
VIDEO / GRAPHICS ENHANCER
VIDEO BANDWIDTH
VIDEO CAMERA
VIDEO DISC
VIDEO EDITING
VIDEO GAIN
VIDEO MIXER
VIDEO PRINTER
VIDEO WALL
VIDEOCONFERENCE
VITC
VOD
VSWR
VECTORSCOPE
An electronic test machine for color video systems, for color problem tracing and correction in a TV or video studio. The vectorscope, which is similar in appearance to an oscilloscope, displays color vectors and components, as well as the relative position of the Color Burst. See also Waveform Monitor.
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VERTICAL INTERVAL SWITCHING (VIS)
When one video signal replaces another, the switching process causes a random interruption in the first video signal (in the midst of a frame) and a random entrance into the second video signal (also in the middle of a frame). The result is a visible jump in the edited or viewed image. This situation is amplified when the tape is copied, and the disturbance on playback is much more serious. To avoid this phenomenon, switching is performed at a very specific point during the vertical blanking retrace period which is also known as the vertical interval. This allows very smooth replacement of a whole frame by a second whole frame provided that the video sources are Genlocked to each other. VIS is used also in the presentation and graphics worlds, where sources are switched during the black period of the vertical interval, thus allowing glitch-free transitions.
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VERTICAL TILT
A field-time distortion which changes the shape of a flat, low frequency video signal and is visible as dark or light bars at the beginning or end of the picture on the screen. Vertical tilt is usually caused by poor low frequency response, mainly of AC coupled circuitry. Vertical tilt in professional applications should not exceed 0.5%.
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VGA (Video Graphics Array)
A color graphic standard introduced by IBM for personal computers, which displays either high resolution graphics (640 x 480) or 256 colors simultaneously, albeit at low resolution. Due to excellent aspect ratio, which resembles the standard video aspect ratio, VGA is suitable for video recording (after scan conversion and encoding).
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VHS
Video Home System. A format developed by JVC™ utilizing half-inch tape, which is the most widely used analog video format.
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VHS-C
A standard VHS system utilizing a compact cassette which, although it has less recording time, is very convenient for camcorders. Special adapters allow these small cassettes to be used in regular VHS recorders.
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VIDEO / GRAPHICS ENHANCER
A general term used for a device which corrects problems on a video or a graphic image. A narrower definition is a machine which restores high frequency losses by enhancing the high frequency region of the video/graphics spectrum. An enhancer often has controls such as Sharpness, Definition, Detail, etc., which are used for high frequency boosting. Unfortunately, there is sometimes a tendency for analog enhancers to introduce snow while adjusting the high frequency region of the spectrum. Image enhancing is done in the digital and graphics domains as well, usually using different technologies, albeit with the same purpose and uses as the analog video enhancer.
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VIDEO BANDWIDTH
The highest signal frequency that the video signal can reach. The higher the video bandwidth - the better the quality of the picture. A video recorder that can produce a very broad video bandwidth generates a very detailed, high quality picture on the screen. Video bandwidth requirements for studio work may vary from 5 and 200 MHz. Component video and graphics may reach bandwidths up to 500 MHz and higher.
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VIDEO CAMERA
A camera which contains an electronic image sensing CCD (Charged Coupled Device) rather than photographic film. The CCD is scanned rapidly converting light rays to electric signals. A video camera has additional electronic circuitry which generates color and sync pulses. Some cameras are equipped with audio circuitry, e.g., microphone, audio amplifier and additional audio electronics. Professional cameras, in order to obtain a better picture, have a triple CCD system (three tubes in the past) - one for each basic color - red, green and blue. Most professional cameras have a genlocking input, which allows the camera to be synchronized to an external source. Some cameras include additional electronic circuitry such as character generators for titling and special effects, Tally, etc. CMOS type sensors are also used for some types of cameras. Those sensors are relatively inexpensive to manufacture.
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VIDEO DISC
An obsolete medium used for recording audio and video information on a disc the size of a regular LP record. There are several recording methods available. Video picture quality is quite high, but lack of re-recording capability limits the use of this system. It was replaced by the DVD.
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VIDEO EDITING
A procedure used for combining selected portions of several video footages, or of the same footage, in order to create a new, edited version. A variety of editing consoles are available which meet several standards, e.g., 1/2 inch, 3/4 inch, etc. During video editing, special effects such as cross fading, inserts, 3D effects, etc. can be added. Professional editing uses a special time code, which is printed on every frame of the magnetic or optical media. This allows for very accurate revision down to the level of a single frame. Very often, audio editing is carried out simultaneously with video editing. The PAUSE control of a VCR can do simple cut-to-cut editing. In the digital domain NLE (Non Linear Editing) systems are used nowadays, which are fully digital, mainly computer based systems. The NLE system is hardware and software based, allowing for much more versatility and effects creation.
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VIDEO GAIN
A nominal video signal level is usually 1 volt for Composite video, 0.7 Volts for component or RGB video or 0.3 Volts for the chrominance subsection, at which level a fully saturated picture is transmitted to the acceptor. However, for cases where the video signal is attenuated, a low-noise, high-gain analog amplifier is built into quality video processing equipment. This amplifier provides video gain control whereby the video signal can be boosted or reduced. Dark pictures resulting from low level lighting are easily adjusted. An additional benefit of good video gain equipment is the ability to fade out pictures, for editing purposes.
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VIDEO MIXER
A device used to combine video signals from two or more sources. Synchronized inputs are mixed with each other and various special effects patterns and shapes are added in accordance with the proficiency of the video mixer being used. Two pictures can be superimposed, one on the other, while a third picture is cut into a “hole” in the scene. A video mixer usually generates sync signals allowing genlocking of additional video sources to the first source. Video mixing is done nowadays digitally with digitized analog or native digital sources.
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VIDEO PRINTER
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VIDEO WALL
A video wall is large screen made up of several monitors, placed close to one another, which, when viewed from some distance look like a large video screen or wall. A digital processor breaks down the original video or graphic image into several pieces, by converting the analog video signal to digital, rescanning and resampling it, and generating individual analog video outputs for each monitor. The unit is relatively expensive, and is used, as are wide screen projectors, mainly for public viewing.
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VIDEOCONFERENCE
A “virtual” conference of a group of people at different locations, using video cameras, monitors, microphones and loudspeaker systems. The popular linking methods between the sites are multiple ISDN lines, DSL or some other fast internet/network system.
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VITC
Vertical Interval Time Code is the most popular method for inserting and reading time codes on a videotape or disk. The time code is ins erted in the vertical interval (the screen blanking period) of the video signal, where it is not apparent on the screen, and a time code reader easily retrieves it. The system consists of a time code generator to insert the information, and a time code reader to retrieve it. In most cases, both units - the generator and reader - are built in to one machine. The VITC system is very reliable, as each and every frame of the video signal has its individual time code and mark.
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VOD
Video On Demand. A system which allows a user to select a video movie to be displayed on his TV at any selected time. The requests are transmitted to the center either by an Interactive TV system via a standard or cable modem, or via a PC and a telephone link. More limited systems are called Near VOD where freedom of choice is more limited. VOD requires a bi-directional CATV (upstream/downstream) system.
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VSWR
(рус. КСВН)
Voltage Standing Wave Ratio. A term used to evaluate and measure impedance matching in high frequency electronic circuitry and transmission media (coax cables etc.), in order to achieve best signal transmission.
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