LAYER II
LCD
LINE COMPENSATION
LINE DOUBLER/ QUADRUPLER/SCALER
LINE-UP
LNA/LNB
LOAD RESISTANCE
LOGO GENERATOR/INSERTER
LOOPING
LOUDSPEAKER
LTC
LUMA NOISE
LUMEN
LUMINANCE
LUX
LVDS
LZW
LAYER II
A subset of the Audio part in the MPEG-1 and MPEG-2 standards. Some of its definitions are - 32-384 kbits/sec, sampling rates of 16-48 kHz etc.
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LCD
(рус. ЖКД)
Liquid Crystal Display. A screen for displaying text and graphics based on liquid crystal technology, where minute currents change the transparency of the screen. The advantages of LCD screens are very low power consumption (can easily be battery driven) and the low price of mass-produced units. The LCD system first became wide spread in digital wristwatches which can operate for a very long time on small batteries. The disadvantages of LCD were narrow-viewing angles, slow response (the first ones were too slow to be used for video), invisibility in the dark unless the display is backlit, and difficulties in displaying true colors on color LCD displays. With the introduction of new technology and especially TFT driven LCD displays, picture quality began resembling the quality of a CRT (the Cathode Ray Tube used in televisions and monitors). Brightness has improved dramatically and the price is dropping constantly. New large active LCD (TFT driven) displays are replacing TV tubes, but are still quite pricy. When the prices of large LCD screens start approaching the prices of CRTs, they will inevitably replace most home TV sets, and will provide, at a reasonable cost, a TV which can be hung on the wall like a picture.
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LINE COMPENSATION
Use of a video line amplifier/compensator (equalizer, EQ.) to pre-compensate for high frequency loss resulting from transmission of video signals over long cable distances (several hundred meters). Deterioration in the picture takes the form of loss of fine details and color distortion. Sometimes the entire video signal, including sync information, is severely attenuated. The analog line amplifier is usually installed at the beginning of the line. In the digital domain, a similar process is used – also called EQ., which employs high digital amplification stages and sometimes another process called reclocking, which is similar to analog TBC operation.
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LINE DOUBLER/ QUADRUPLER/SCALER
In its simple form, a device which converts a video signal to a high frequency computer DATA type signal. It is intended primarily for displaying video on a VGA monitor or on a DATA wide screen projector. An ADC is applied to the video signal, reading it into RAM (Random Access Memory), adding lines and shifting the data to use high frequency scan rates as used by computers, and then passing the signal through a DAC in order to obtain an analog signal. Those devices are sometimes also called de-interlacers as they convert an interlaced video signal to a non-interlaced signal. See also Scaler.
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LINE-UP
A test signal recorded at the beginning of a tape, comprising an audio and a video signal, which is used as a reference for future recording and playback.
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LNA/LNB
Low Noise Amplifier / Low Noise Block down-converter. Amplification equipment used near a satellite-receiving dish, for low noise amplification and frequency shifting, before the signal enters the satellite receiver.
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LOAD RESISTANCE
The resistance impedance that a properly terminated cable places on the signal transmitted through it. In the case of a high frequency signal, signal-to-cable matching is essential to prevent signal deterioration. A specific load resistance (which is equal to the cables characteristic impedance) should terminate the cable, which in video is usually 75 ohms. Improper cable loading results in signal distortion, ghost images, color loss and other adverse phenomena. The source resistance should be equal to that of the cables impedance and the load resistance.
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LOGO GENERATOR/INSERTER
A machine used in broadcast and video production studios for generating a logo, to be displayed on the screen, usually in a specified corner. The logo, which is a graphic symbol, is usually stored on a ROM (Read Only Memory) or a flash memory chip and is keyed into the video picture upon request. Today, the classic generated logo has been replaced by a PC generated logo, encrypted into the video image using Genlock equipment. The computerized PC logo generator allows more flexibility in logo generation providing more graphic and eye-catching tools and is easier to use. Most logo generators/inserters contain more than one logo in their memory. Logos maybe uploaded to the machine from a PC directly (RS-232, USB, Firewire) or via a floppy disk reader which is built-in the inserter. Logos may be generated using graphic images, short animations or resized video files.
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LOOPING
A term used to describe the cascading or chaining of a video signal to several video machines (distribution amplifiers, VCRs, monitors, etc.). For example, a VCR is hooked up to a distribution amplifier, which has a video-input connector, and a loop output connector. When a signal is transmitted to the first machine through the input socket, it is fed, as an unprocessed signal, through the loop output connector (parallel connection) to the second machine. In turn, exactly the same signal is fed to a third device which is attached to the second one, and so on. Thus a very large number of VCRs or other video devices can be looped together for multiple processing. Proper signal terminations should be noted. In a large cascaded setup, signal termination is normally applied at the last machine in the chain.
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LOUDSPEAKER
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LTC
Longitudinal Timecode. Another system for encrypting Timecode on a tape (see Timecode, VITC). This system uses an audio track for Timecode recording.
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LUMA NOISE
Noise which manifests itself in a video picture as white snow. It is the product of one or more of the following factors: low signal level due to poor lighting conditions, a poorly-manufactured video device, low quality video tapes, excessively long video cables used without pre-compensation, dirt on the video recorder heads which interferes with reading and writing, and over-enhancement of the video signal. Good quality video processors do not generate Luma noise. They maintain an excellent enhancement level, without sacrificing picture quality, by using noise gates. Snow can easily be reduced or eliminated in poorly recorded tapes and a clean copy can be created. In the digital domain, Luma noise may be a result of poor digitization processes, signal jitter (digital clock related problems), logic level incompatibility and similar voltage-related reasons.
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LUMEN
(рус. Люмен)
A measure of light intensity. Approximately one-foot candle dispersed on a square foot.
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LUMINANCE
(рус. Люмен)
A video signal includes luminance, chrominance (color information), and sync. Luminance is the photometric measure of the brightness in a video picture. If luminance is high, the picture is bright and if it is low the picture is dark. Thus, luminance is the black and white part of the picture. Changing the chrominance level will not affect the brightness of the picture.
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LUX
(рус. Люкс)
A method used in photography for measuring the energy density of light, and for comparing sensitivities of cameras. (1 Foot-candle =10.76 Lux or one Lux=1 Lumen/square meter).
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LVDS
(рус. Люкс)
Low Voltage Differential Signal. A signal format used for connection, for example between a notebook and an LCD monitor.
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LZW
(рус. Люкс)
Lempel, Ziv and Welch. Compression and encoding method named after the inventors, which analyzes a file - even a color file, and reduces its size by checking redundancy of patterns.
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