Glossary

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GLOSSARY A B C D E F G H I J KRAMER K L M N O P Q R S T U V W X Y Z GLOSSARY Common Terms Used in Video ! AES/EBU A digital audio standard established by the Audio Engineering Society and the European Broadcasting Union. The signal is serial digital, comprising two channels. The basic sampling resolution is 20 bit, sampled at frequencies between 32 kHz and 48 kHz (44.1 kHz is the most common). Two sets of 4 bits of information are included for other data transmission (one set can be added to the 20 bit of audio, for a 24 bit system). Additional bits are transmitted as well, and the transmitted frames of the interwoven audio channels are grouped to frame blocks. ! ALIASING NOISE An artifact created while an ADC converts an analog signal to digital form and the sampling rate of the converter is less than double the highest frequency component within the analog signal or one of its harmonics. ! ANALOG VIDEO SIGNAL Signal in which the output varies as a continuous function of the input, while the values of the transmitted information are within defined limits. Any variation in an analog video signal may represent a specific video parameter, e.g., when the luminance signal is high (1 V) the picture is very bright. When the signal is low (0.1 V), the picture is very dark; at 0 V the picture is totally black. TTL digital signals, in contrast, are predefined as only 0 or 5 V or other fixed logic levels and do not vary. ! ANCILLARY DATA Data added to a digital video data stream including information such as embedded digital audio, control signals, etc. ! ANSI American National Standards Institute. ! ANTIALIASING Antialiasing is a procedure which, by smoothing and filtering, eliminates or reduces, aliasing noise. The procedure usually involves low pass filtering of the processed signal prior to digitizing in order to eliminate signals, having frequencies close to and greater than half of the sampling frequency. ! APL Average Picture Level. A measure of average video luminance level expressed as percent of maximal white level. When the APL is low, the picture is dark, when the APL is high the picture is bright. GLOSSARY Page 12.1 ! ASPECT RATIO The ratio between the width and height of the TV picture on the screen. In a normal TV set or monitor the aspect ratio is 4 to 3 (4:3). The new aspect ratio in HDTV and IDTV/EDTV is 16:9, which resembles the aspect ratio in a movie theatre (Widescreen). New TV systems support both 4:3 and 16:9 aspect ratio (PAL PLUS) and can automatically switch between them. ! AUDIO BANDWIDTH The range of audio frequencies over which an amplifier or receiver will respond and provide useful output. The higher the audio bandwidth the better the sound quality. The highest practical frequency for the human ear is 20 kHz. An audio amplifier delivering a flat response of up to 20 kHz will faithfully reproduce the audio soundtrack of a video recording. ! AUDIO-FOLLOW-VIDEO SWITCHER During video production, the video signal is normally accompanied by an audio signal. Sometimes, during the switching or processing of signals, the audio signal is separated from the video signal. In such a case, a complex situation arises whereby each signal must be processed, mixed and enhanced separately. Audio-follow-video is a process which overcomes this difficulty and both signals, audio and video, are switched from an audio-video source to an audio-video acceptor simultaneously (not in separate passes). ! AUDIO-VIDEO COMBINER A device which combines audio and video signals. In the analog world it describes a machine, such as one which modulates the audio signal on a high frequency carrier and mixes it with the video signal for transmission on a single cable. In the digital world it describes a device which embeds digital audio signals within a digital video signal. ! BACK PORCH A part of the composite video signal which is between the trailing edge of the horizontal sync and the beginning of the corresponding active video line (end of horizontal blanking). ! BALANCED SIGNAL A signal that is divided into two antiphase signals, traveling on two wires (and sometimes with a third - a ground reference wire). Transmitting a balanced signal achieves better signal to noise ratio, and the signal is more immune to noise and interference. The receiving end requires a differential amplifier, which amplifies only the differences between the antiphase signals, thus canceling noise picked up on the way. The balanced system is used either when very low signals are to be transmitted over long distances (such as those generated from high quality microphones) or at broadcast audio studios for highest quality signal recreation. The balanced signal system is used in TP (Twisted Pair) wire setups when it is essential to use non-coaxial wires for data, video or audio transmissions. ! BASEBAND VIDEO Normally refers to a non-modulated composite video signal, with frequency spectrum extending from a few Hertz (DC) up to several MHz, and covering the full bandwidth of the video signal. GLOSSARY Page 12.2 ! BETACAM-SX A digital video format introduced by SONY™. This format uses MPEG compression with a data rate of 18Mbits/sec. The compression ratio is high - approaching 10:1. Output quality is very good despite the high compression ratio because it uses an MPEG-2 4:2:2 profile. Cassettes use metal particles technology and come in two sizes 60 minutes for fieldwork and 184 minutes for studios. These VCRs also play analog Beta tapes, for backward compatibility. ! BLACK BURST A video signal comprising sync and color burst signals which produces a black image on the screen. It is used to genlock other video sources to the same sync and color information. Black burst generators are used in video studios to genlock an entire studio to the same signal for easier switching and mixing between sources. ! BLACK LEVEL That level of the DC voltage of a particular part of the video signal which corresponds to the black areas in a video scene. The black level is used as a reference for comparison with other tones in the picture and other video signals. ! BLACK LEVEL CLAMPING An electronic process, which establishes a fixed DC level for a picture signal at the beginning of each scanning line. The black level of a video signal is set to a specific, predefined DC voltage. This process is used, for example, when two video signals are to be mixed and the black levels must therefore be equal. ! BLANKING RETRACE PERIOD The period when the screen is darkened; this occurs when the electron ray in a monitor or a TV set retraces to start a new line or a new field. The instantaneous amplitude of that signal is such that it makes the return trace invisible. The blanking period is used to eliminate the appearance of the CRT retrace beam so it will not be visible on the monitor. Switching done during the retrace period results in "clean switching". (See Vertical Interval Switching.) ! BLOOMING A disturbing phenomena apparent when a part of the video picture becomes “brighter than white” due to wrong exposure or due to a very strong light source shining directly into the camera lens. The blooming effect distorts the colors and the fine details of the area affected by the strong light. This effect can also be seen when a color decoder chip within a TV set or monitor is wrongly tuned or malfunctions. In order to check whether the blooming effect is a result of a badly illuminated scene or a malfunctioning monitor, the signal should be fed to another good monitor. If the effect persists, it shows that the video source is defective. ! BOUNCE SIGNAL A special, artificially generated video signal for testing, where the APL is changed at a low rate, testing the low frequency response of a video device as well as black level clamping. GLOSSARY Page 12.3 ! CABLE EQUALIZATION An electronic process compensating for high frequency losses incurring in long coaxial cables due to various cable shortcomings. Equalization is usually performed by special controls or trimmers mounted on the amplifier or switcher which allow variable operation to equalize different cable lengths and qualities. Equalization is best done at the source amplifier, at the beginning of the long cable, to preserve optimal signal to noise ratio. Cable equalization (EQ) is also important for fast digital signals. For digital signals, cable EQ is done at the end of the cable. In this case the equalization is usually automatic and no user trimming is required. ! CCD (Charge Coupled Device) A microelectronics chip which stores minute electric charges on a matrix of microcapacitors. These voltages are bucketed (in the sense of a bucket brigade) from one address to another according to an external-clocking signal. This permits storage of analog memory on the chip. CCD technology is used in audio to store a signal, which can be retrieved later to create an echo effect via retrieval delay. In video, CCDs are at the heart of video cameras. Lenses cast a beam of light on the CCD, which acts as a sensor and temporarily stores the visual image. CCDs were used to store a video signal, which was later retrieved for time base correction. Digitally storing video information is performed nowadays using fast RAM chips. ! CCIR Comite Consulatif International des Radiocommunications. A European committee which was situated in Paris and created and approved standards related to Audio and Video. The committee is no longer active and has been replaced by the International Telecommunication Union (ITU.) ! CCIR 601 Specifications and parameters for application of Component Video signals (Y, Cr, Cb) in a 4:2:2 system, recommended by the CCIR, now known as ITU-R BT.601-2. ! CHROMA NOISE Noise which manifests itself in a video picture as colored snow. It is the product of one of the following factors: 1. The Chrominance in the video signal is weak. 2. There is excessive color information, which creates over-saturation. 3. A poorly manufactured video device. 4. Low quality videotapes. 5. Poor color decoding. Good color processors reduce or eliminate Chroma noise. ! CHROMA KEY A process available on better quality special-effects generators and mixers which allows superimposition or replacement of one video picture in a predetermined area of another one. The first picture is photographed with an object or person against a special, singlecolor background. The complete color content of this particular signal is removed and the second picture is inserted in the area where the background was. GLOSSARY Page 12.4 ! CLAMPING An electronic process, which corrects, line-by-line, the video blanking level or sync tips by clamping it to a predefined DC level. The process reduces the DC level changes when switching between different sources, eliminates picture jumps on the screen and the accumulation of low frequency noise and instability. Clamping also increases the dynamic range of video amplifiers by limiting the average picture changes, which stress the video amplifiers. ! CLIFF EFFECT Analog signal quality gradually degrades with cable length. Digital signals behave differently. Up to a certain distance, depending on equipment and cables used, the signal is perfect. Extending the cable length by only a few meters beyond that distance may cause a total signal crash, which is known as the Cliff Effect. ! COLOR PHASE The timing relationship in a video signal, which keeps the hue of a color signal correct, measured in degrees. Color information is encoded in the video signal as the difference in phase between the sine peaks of the Chrominance signal and the color burst subcarrier signal. If the two signals overlap exactly, then the phase difference is designated as zero degrees. If the sine signals do not overlap, the color phase can vary from 0 to 360 degrees. Each shift in the color phase represents a specific tint on the screen. If two sine waves are shifted one from the other by 180 degrees, then the colors are totally inverted. ! COLOR SUBCARRIER A standard monochrome video signal must have additional modulation frequency bands (sidebands) added in order to convey color information. These are the color subcarrier components. Using the color burst as a reference, the ratio of the color subcarrier of the video signal to the burst indicates the intensity of the colors (in PAL and NTSC). Thus, when there are relatively limited color subcarrier components in the video signal, the colors are weak or pale. The system is, in fact, a little more complicated than this since in PAL and NTSC the color subcarrier contains red and blue information simultaneously which must be further processed by a color decoder in the monitor, to RGB. The color subcarrier frequency in PAL is about 4.43 MHz and in NTSC it is about 3.58 MHz. Since it resides close to the highest luminance frequencies, the usable luminance frequency when using simple analog filters is limited to about 4 MHz in PAL and 3 MHz in NTSC. The luminance frequency response after separating Chrominance from luminance may be much higher when using a digital Comb Filter. ! COMB FILTER Circuitry designed for best separation of Y and C from a composite video signal. Standard circuitry uses analog bandpass and bandstop filters, which result in unclean separation of Luma from Chroma, possible phase shifts (hue changes), signal delays and a host of other unwanted effects. Comb filtering is a digital process, separating Y from C, based on “combing” out the Chrominance signal from the luminance. It is called comb filtering because Chroma resides in specific bands along the frequency axis which resemble a comb. The drawbacks of digital comb filtering are some unwanted effects due to digitization of the GLOSSARY Page 12.5 video signal, higher cost than analog filters and sometimes the need for time base correction prior to “combing” in order to obtain the best results. ! COMMUNICATION PROTOCOL Software based protocol or language, linking several devices to enable them to communicate one with the other. Communication protocols are used between computers and VCRs or editing controllers allowing bi-directional conversation between the units. The linked units use specific hardware connections in addition to the software and protocol. See also RS-232/RS-422. ! COMPONENT VIDEO A simple composite video signal comprises luminance information, color information (Chrominance) and sync information in one transmission channel. When performing video image improvement operations and special effects generation on a composite video signal, a trade-off between color quality and picture resolution is unavoidable. To achieve maximum video quality, professional equipment therefore uses one of several component systems, which split the signal into several channels: RGB splits the video signal into its red, green, blue, and sync components. The YUV system uses a different set of components: luminance + sync, and red/blue color difference. The Super Video (Y/C - Super-VHS and Hi-8) system separates the luminance and Chrominance components. Different types of equipment are required for each format and each component system has its own advantages and disadvantages. In a video studio, it is not uncommon to find a composite or Y/C video recorder, an RGB camera and a component YUV mixer. Special interface units are needed to bridge between the various formats of component video. ! COMPONENT DIGITAL A digital form of Component Analog signals usually related to CCIR 601 (ITU-R BT. 601-2.) ! COUPLING A way to interface between two machines or signals. In video and audio, coupling can be direct – called DC coupling; through capacitors – called AC coupling; using transformers – called inductive coupling; by opto devices - using optocouplers or using RF (radio frequency) transmitters and receivers. DC coupling preserves the original DC levels of the signals and insures maximum signal flatness. However, erroneous DC levels, if they exist, are transferred between the machines and may cause damage. AC coupling practically isolates the two machines or signals from their respective DC components, but has the problem of poor low frequency response and signal breathing effect. For example, video switchers and DAs may have AC or DC coupling either at the inputs, outputs or both. A smart system allows the user to decide which way the signals should be coupled to and from the DA or switcher. Transformer coupling is problematic in the video field, mainly because of bandwidth considerations, as the transformer should perform equally in all relevant frequencies, and magnetic core transformers hardly ever do so, especially when a true flat response is needed. Transformer coupling is used in the audio field mainly for maintaining proper balanced signals, for impedance matching and for ground isolation - as ground loops may be quite harmful in audio. GLOSSARY Page 12.6 Opto-coupling in video is mainly used to link up devices in remote locations, by using fiber optics technology instead of coaxial connections, thus extending substantially the range of operation. RF connection is mainly used in radio, TV and cable transmissions, in microwave links node to node for ENG and in satellite transmissions. RF modulators and demodulators are needed to maintain the link. RF offers the longest connection range of all systems, crossing continents, oceans and even outer space. ! Cr, Cb Digital red and blue color difference signals. ! CROSSTALK The interference of one signal by an adjacent one caused by stray electromagnetic or electrostatic energy. In audio, crosstalk results from leakage, for example, between the left and the right channels or between different inputs. In video, crosstalk between input channels can be classified into two basic categories: luminance /sync crosstalk and color (Chroma) crosstalk. When crosstalk in video is too high, images from one source appear as ghosts on the other. Low crosstalk is an essential feature for any audio and video device and is based on accurate design and proper signal handling. Crosstalk risk gets higher with higher signal frequencies. ! D1 A recording format utilizing a 19 mm-wide (3/4") video tape and digital component video signals conforming to the ITU-R BT.601-2 (CCIR 601) standard. ! D2 A recording format utilizing a 19 mm-wide (3/4") video tape and digital composite video signals conforming to the SMPTE 244M standard. ! D3 A recording format utilizing a 1/2"-wide video tape and digital composite video signals conforming to the SMPTE 244M standard. ! D5 A recording format utilizing a 1/2"-wide video tape and digital component video signals. ! D9 Another name for Digital-S, the digital s-Video (YC) format. ! dB Decibel. A logarithmic ratio measuring signal amplitude and power, allowing easy evaluation of very large or very small ratios. ! DCT Discrete Cosine Transform. One of the algorithms (software formulas) used in data compression. This algorithm is widely used in image and movie compression (JPEG and MPEG). GLOSSARY Page 12.7 ! DECIMATION A digital method for "eliminating" redundant pixels in an image. The process is widely used for image scaling and for oversampled ADC's. If every second pixel is stored in a digital image storing apparatus, the decimation factor is 2, and the image size occupies only one quarter of the original size. Decimation of a high order deteriorates the signal and unwanted artifacts are added to the picture, whether it is a video or still picture. ! DECIMATION FILTER A filter built in decimation circuitry designed to reduce or eliminate the unwanted effects of the decimation process. ! DELAY CORRECTION When an electronic signal travels through electronic circuitry or through a coaxial cable, delay problems may occur. The result of the delay in video is usually a blurred (ghostly, shadowed) image and special electronic circuitry is needed to correct it. Delay correction functions are found on all better video processing equipment. A common problem in analog video is the difference of delay between the luminance and the Chrominance channels of the image, resulting in colors that look wrong. ! DIFFERENTIAL GAIN A measure of non-linearity related to a composite video signal amplifier/processor. It is measured by comparing two initially equal amplitudes of Chrominance signals riding on two different luminance levels. The inaccuracy is measured as a percentage. ! DIFFERENTIAL PHASE A measure of non-linearity related to a composite video signal amplifier/processor. It is measured by comparing two initially equal phases of Chrominance signals riding on two different luminance levels. The inaccuracy is measured in degrees. ! DIGITAL-S A digital video format introduced by JVC™. This format is “back” compatible with the S-VHS format so cassettes recorded in S-VHS can be used with a DIGITAL-S VCR. The technical specifications are very similar to the DVCPRO format - 4:2:2 encoding, 3.3:1 DCT compression and a 50 Mbits/sec data rate. The cassette lasts for 104 minutes and is 0.5 inch wide. ! DISTRIBUTION AMPLIFIER A device which distributes one video and/or audio source to several video/audio acceptors for simultaneous recording or monitoring. A good quality distribution amplifier amplifies the incoming signal (video and audio), pre-compensates the signal for potential losses (resulting from the use of long cables, for example) and generates several identical buffered and amplified outputs. Distribution amplifiers are mainly used in duplication studios where many copies of a tape must be simultaneously generated from one source. Often, a video processor is inserted between the source and the distribution amplifier for correction and fine-tuning of the source signal before multiplication, so that all copies are corrected in the same way. GLOSSARY Page 12.8 ! DROPOUT Partial loss of a video picture, usually seen on the screen as white streaks, resulting in a poor quality playback. Flaws in magnetic tape coating resulting in loss of magnetic particles from the tape are the main cause of dropout. Special electronic equipment usually digitally based, is needed to eliminate dropout effects, named dropout compensators. Normally, a dropout compensator replaces the missing information due to drop out with data from adjacent pixels, lines or fields. ! DV Digital Video. A format initially used by SONY ™ for the output of a digital camera or VCR. The DV format uses a special communication protocol: IEEE1394 (a.k.a. Firewire, iLink). The format is basically a digital component video format (YUV). In PAL it is based on 50 fields/sec and 625 lines per frame and the encoding system is 4:2:0. In NTSC there are 60 fields/sec and 525 lines (similar to the analog format) and the encoding system is 4:1:1. The audio part of the DV format is digitally encoded but uncompressed, with sampling rates that can be selected by the user - 44.1 kHz @16bits for two sound channels (similar to an audio CD). At 12 bit and 32 kHz sampling rate, four audio channels can be used. The compression rate is about 5:1 and the standard provides a 25Mbit/sec data rate. Every compressed frame is fed in parallel to ten channels during recording (NTSC) or to 12 channels (PAL), therefore, dropout effect becomes almost obsolete. There are two cassette sizes for this format: a mini cassette for up to 60 minutes of recording and a regular cassette for up to 240 minutes of recording. ! DVB Digital Video Broadcast. The system proposed for digital video broadcast in Europe and is similar to analog TV broadcast. The system is based on satellite transmission, groundbased receivers and the video signal is MPEG-2 encoded. ! DVCAM A digital video format introduced by SONY™. This format uses DV like cassettes, has a 4:1:1 encoding scheme and outputs a 25Mbits/sec data rate. Cassettes come in two sizes- 46 minutes for field use and 180 minutes for desktop VCRs. ! DVCPRO A digital component video format introduced by Panasonic™ and Philips BTS™. The format uses two cassette sizes- 6.35mm and 0.5 inch. It provides a stream of digital information @ 25 Mbits/sec and has two uncompressed audio channels. It operated initially at 4:1:1 encoding and 5:1 DCT compression, but was recently re-introduced at 4:2:2 encoding and a lower, 3:3:1, rate of compression. This has changed the amount of time that can be recorded on tape from 123 minutes for the desktop DVCPRO VCR operating at 4:1:1 to 61.5 minutes at 4:2:2. ! DVD Digital Versatile Disk (or Digital Video Disk). A recently introduced video media, allowing playback of video and audio from a digitally recorded disk which resembles a CD. The disk allows playback of a full feature movie of more than 2 hours. MPEG compression is used for recording. The audio section is digitally recorded as well, with various surround sound schemes, such as Dolby AC3. The world was divided into GLOSSARY Page 12.9 several “zones” incompatible with each other. Several different standards exist, similar to PAL and NTSC, and some manufacturers have released Multi-standard / Multi-zone players. Copy protection schemes are built into the DVD player in order to avoid piracy. The single layer DVD capacity is about 4.7 gigabytes and the double layer capacity is 8.5 gigabytes. DVD players are available for the PC as well, which also allow playback of regular data CD-ROMs as well as music CDs. Recordable DVD (named DVD RAM or DVD RW) have recently been introduced. Deliberations on the final standard, though already agreed upon by many manufacturers, were reopened recently and therefore, the final format is not yet set. It is not unlikely that several DVD recording formats will co-exist in the future, which will be very confusing for the end users. In DVD, as the signals are recorded digitally, quality is expected to be very high, and fast, random access to any part of a movie will allow fast and easy editing. Once released, the same very high-density media can also be used for computer data recording and archiving. ! DVI Digital Video Interface. Used in Multimedia applications, where computer generated text and graphics are merged into a video production, for educational, advertising and post-production purposes. The DVI is based on specific chip-sets designed for this application. ! EAV End of Active Video. A digital code used with digital component video signals, marking the end of a video line. ! EBU European Broadcasting Union. A European organization of broadcasters which among other activities, defines recommendations and statements for the 625/50 line television system. ! ENCODING (COLOR) A process which translates several signals of information simultaneously from an analog or digital form to a coded form, without an apparent loss of image quality. An encoder usually accepts RGB or YUV inputs from either an analog or a digital source and converts these signals to a full-colored composite or Y/C video signal. In essence this device performs the opposite of a color decoder. ! ENHANCING (VIDEO IMAGE) Improving a video image by boosting high frequency or other signals which are lost during recording. There are several types of enhancing. Luminance enhancing takes place mainly in the border areas between light and dark images. The transition edge between the light and dark areas is extenuated. When there is a light area on the screen located on a dark background, the edge of the left part of the area becomes lighter and the right side becomes darker. In double-edge enhancing, all the edges surrounding the area become enhanced and the enhanced area itself becomes, in effect, threedimensional looking. Chrominance enhancing improves color saturation and restores normal hue. GLOSSARY Page 12.10 ! EQUALIZING PULSES Synchronization pulses of double frequency and of short period leading and following the vertical sync. Proper equalizing pulses are needed for picture stability on the screen, for proper vertical deflection, interlacing and for PAL switch generation. Missing or distorted equalizing pulses can cause misalignment of the video image on the screen, skewing effect, color distortion and loss. ! FIBER OPTICS A medium for transmitting analog and digital signals which is made of translucent fibers with appropriate interfaces, using light to represent the signals. The original signals are recovered back to electronic signals at the remote edge of the fiber. The optical fiber system provides high electrical isolation between transmitter and receiver, as well as immunity to electromagnetic and static interference. The signal loss in a Fiber Optics system is usually smaller than in coax cables, and therefore optic fibers are used to carry signals over very long distances (tens and hundreds of kilometers.) ! FLICKER Annoying visual phenomena mainly related to the interlacing of video fields, which show up as small vibrations on the screen. Flicker also appears when static images are displayed on the screen, as in computer generated text when transferred to video. Poor digital image treatment, as in low priced standards converters (going between PAL to NTSC), will create an annoying flicker on the screen. There are several electronic techniques to minimize flicker, such as line averaging and filtering. ! FOUR Fsc (4Fsc) The sampling rate of composite video signals as a multiple of color subcarrier frequency. In PAL 4Fsc is about 17.73 MHz and in NTSC it is about 14.31MHz. ! FOUR:ZERO:ZERO (4:0:0) A monochrome video format mainly used for key signals in a video production studio. ! FOUR:TWO:TWO (4:2:2) A term used in digital component video formats and interfaces. 4:2:2 states the ratio of the sampling rate of the luminance channel (it was 4xFsc, and is now 13.5 Ms/s) to the rate of sampling of the two color difference signals (it was 2xFsc each, and is now 6.75 Ms/s). Sampling the color information at lower rates is allowed due to the limited bandwidth of color information. This is one of the formats of the CCIR 601 recommendations. ! FOUR:FOUR:FOUR (4:4:4) A term used in digital component video formats and interfaces. The term describes 3 full bandwidth channels, like R, G, B, each being digitized at 4Fsc. ! FRAME SYNCHRONIZER An electronic device utilizing digital technology, with several video inputs. The Frame Synchronizer synchronizes and genlocks sync and color of one input to those of another. After frame synchronization, the two video images can be blended, wiped and processed as they use the same sync and color subcarrier frequencies and the same phase. GLOSSARY Page 12.11 ! FRONT PORCH A part of the composite video signal which resides in the blanking period, between the end of the active line (the leading edge of the horizontal blanking period) and the leading edge of the horizontal sync. ! GAMMA CORRECTION A process used in video and computer graphics images mainly to correct internal microcontrast within the image and brightness. For example, Gamma correction can change the ratio in an image between the brightest, specific color component, to the weakest. ! GENERATION LOSS When master analog videotape is duplicated, the second-generation copy is usually inferior in quality to the master. This depreciation, known as generation loss, appears as distortion, lack of details, improper colors, etc. The limited frequency response of video and audio magnetic tapes and the imperfections in electronic circuitry are the main causes of generation loss. Video enhancing equipment is intended to eliminate or reduce generation loss. High quality video processors pre-enhance the video signal to overcome generation loss. Digital video recording and editing are essentially immune to high frequency generation loss, but are prone to instability and other synchronization-related problems. ! GENLOCKING A system of synchronizing two video signals to the same timing and color phase in order to coordinate their colors and syncs. Genlocking permits mixing, cross fading, keying and special effects generation between the two signals. A video camera can be genlocked to a second camera through the Genlock connector on the camera. All professional cameras have genlocking capabilities. Genlocking two VCRs is more difficult and requires the intervention of a sophisticated device called a time base corrector (TBC) or a Framer synchronizer. ! GROUND LOOP Interference that in video may show on the screen as "crawling" vertical bars. A ground loop is created when two elements in a circuit or two different machines connected together receive their ground reference signal from different places. A different ground potential (voltage) creates this loop, interfering with the signal. Special ground-isolation devices are needed to cure the problem. Ground loops are also a problem in audio, where their most disturbing effect is a low frequency oscillation known as "hum" or "motorcycling". Some audio related ground loop problems can be cured by properly reconnecting the ground leading cables to a single point, usually at the most sensitive input area, or at the power supply. Such problems mainly emerge when high amplification is needed, such as when microphones or other sensitive pick-ups are connected to the system. ! HDTV High Definition TV. Several standards were introduced for HDTV broadcast, with much higher resolution on a special TV screen. HDTV or the like - IDTV or EDTV will probably be the system used in the future in broadcast and home. There are two basic standards of HDTV - Analog and Digital. The Analog system is used mainly in GLOSSARY Page 12.12 Japan, while the Digital system was adopted by the US and Europe. Several broadcast stations already transmit HDTV signals, but the price of the receivers is still very high, thus limiting the penetration of HDTV to the home market. The chosen display format for HDTV is 16:9 vs. the classic 4:3 aspect ratio. ! HELICAL SCAN A method of recording video information on VCR tapes. The tape is scanned in a helical (slanted) way rather than horizontally or vertically. The helical scan method packs much more information on a given length of magnetic tape than all other methods. For this reason this method is used in the digital world as well - in DAT and in digital video systems. ! HORIZONTAL TILT A line-time distortion, tilting the edge of a white bar. The phenomenon shows on the screen as white or black streaks, bleeding away from the original position, creating a muddy, fuzzy image on the screen. It is a result of the poor low frequency response of an amplifier, (see Vertical tilt.) Horizontal Tilt should not be greater than 0.5% in professional applications. ! I2C The name of a port and protocol developed and patented by Philips ™ used in industrial and consumer electronic devices. I2C ports are relatively slow, and therefore are most suitable for generation of the control signal effecting a large system. The advantage of this port system is simplicity and that only a small number of interface lines are needed. ! IDTV (EDTV) Improved Definition Television (Enhanced Definition TV). This standard resembles HDTV in output quality without the complexity of the HDTV system. The improved picture quality is achieved by extensive processing carried out in the receiver. No different transmission system is needed. ! IEEE 1394 A recommendation for a fast universal interface and protocol developed by Apple™ and published by the Institute of the Electrical and Electronics Engineers, also called Firewire (iLINK). This standard allows fast interfacing between digital cameras, VCRs, CD-ROMs, hard disks, scanners, graphics cards and editing systems. Data rates of 100Mbit/sec are easily obtained by this standard as well as fast and accurate audio/video synchronization. This standard allows "hot swapping" inputs and outputs, adding to its versatility. Firewire is catching on rapidly in the professional video market due to its simplicity, versatility and the ability to easily interconnect video and computer hardware. ! INTERLACING A system developed for television to carry more channels in the broadcast band. This system reduces transmitted bandwidth to half by displaying each video frame by two interlacing (interwoven) fields. One field carries the even video lines and the other the odd lines. Interlacing causes a certain amount of visible flicker, but in live video it is hardly noticeable. GLOSSARY Page 12.13 Flicker is more disturbing in PAL, where the vertical line frequency is 50 Hz, and two 25 Hz fields are displayed one after the other, than in the 60 Hz NTSC system. Interlacing is used in the computer graphics field as well, where higher resolutions can be displayed on an inexpensive monitor by interlacing the image. However, with static images, such as computer-generated text and graphics converted to video, interlacing causes more annoying flicker. Many manufacturers try to eliminate or minimize the flicker effect related to interlacing by raising the allowable vertical frame frequency in PC monitors to 70 Hz and even higher. ! IRE (INSTITUTE OF RADIO ENGINEERS, North America) The term is also used as a video level measurement unit. In the American NTSC system "0" IRE reference is the blanking level, the sync tip is at -40 IRE and the peak white is at 100 IRE. Therefore, a standard 1-Volt peak to peak video level is equal to 140 IRE units. ! ITU International Telecommunications Union. ! JITTER A term describing instability on the time axis. In video, jitter appears as image vibration and breakdown. Special, mainly digital based equipment, is used to correct jitter (see TBC). Jitter is far more important for digital video signals – SDI signals for example. Digital clock jitter that accumulates along a video transmission line might create an abrupt signal loss (Cliff Effect) and special electronic circuitry is needed to restore stability (see Reclocking). ! JPEG/MPEG Joint Picture Experts Group / Motion Picture Experts Group. Standards of storage and retrieval of compressed still and moving video scenes, as used in multimedia video and computer graphics applications. The standards are based on specific hardware and software algorithms. The JPEG compression system is able to compress graphics files at a 75:1 compression ratio or even more, and can greatly reduce a 24-bit color image for easy storage and transfer. ! K-FACTOR A measure of distortion in a processed video signal, which shows on the screen or on the oscilloscope as overshoots and "ringing". Test equipment generates a special signal - a 2Tpulse - in order to measure this distortion. The distortion level is given as a percentage. ! KEY A control signal that identifies and creates the border of a cutout in a background video image into which another video image is inserted. The key signal can be created and derived from many sources and should be genlocked time-wise to the main and inserted video signals. ! LCD Liquid Crystal Display. A screen for displaying text and graphics based on liquid crystal technology, where minute currents change the transparency of the screen. GLOSSARY Page 12.14 The advantages of LCD screens are: very low power consumption (can easily be battery driven) and 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 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 resembles the quality of a CRT (the Cathode Ray Tube used in televisions and monitors). Brightness has improved dramatically and the price is dropping constantly. There is a good chance that active LCD (TFT driven) displays will replace TV tubes in the near future, thus providing, at a reasonable cost, a TV which may be hung on the wall like a picture. ! 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 distances (several hundred meters). Deterioration in the picture takes the form of loss of fine details and color distortion. Sometimes the whole video signal, including sync information, is severely attenuated. ! LINE DOUBLER/ QUADRUPLER 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 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. The resulting image has higher quality and the sophisticated Doublers use interpolation while adding lines in order to increase picture quality. A Line Quadrupler is an extension of a Line Doubler, adding even more lines to the video signal, displaying video on a 1024x768 or higher resolution monitor or projector. It does the opposite of a VGA to Video Scan Converter. ! LOOPING A term used to describe the cascading or chaining of a video signal to several video machines (distribution amplifiers, VCRs, monitors, etc.). 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 prime 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. ! LUMINANCE 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. GLOSSARY Page 12.15 ! MII A professional video format, utilizing a 1/2-inch metal particle videotape, using component video for recording and playback. The system is being further upgraded to use digital video signals. ! MATRIX SWITCHING An audio-video matrix switcher is a device, which resembles a telephone switchboard. It is an array of electronic switches, which routes a number of audio-video signals to one or more outputs. An audio-video matrix switcher usually has several video and stereo/audio inputs, which can be directed by the user in any combination to various audio-video output devices connected to the switchers. Monitors, VCRs and other output devices can be arranged. The user can direct camera number 1 to VCR number 2 while simultaneously connecting camera number 8 to monitor number 1. The possibilities are almost endless. ! MJPEG Motion JPEG. Each frame/field is compressed to JPEG standards, and the sequence is displayed by sequencing through the JPEG frames. This system provides the best video quality, with little or no artifacts, but needs very fast processing. ! MOIRE A video artifact appearing on the screen as close, jittering color lines. This effect is created in the analog video world where high frequency luminance information creates color beats due to insufficient luminance filtering and shortcomings of the monitor. The TV color decoder mistakenly interprets the high frequency signals as Chrominance information and creates unwanted color fringes. In the digital world this effect arises due to incorrect sampling rate. ! MPEG-1 Motion Picture Expert Group. A system for coding of moving pictures and sound. The data rates are 1.5 Mbits/sec. Layer II audio is a subset of this system. MPEG-1 is used for CD audio and video. ! MPEG-2 A collection of definitions for digital audio and video compression used in digital video and audio transmission and play back. Definitions of this standard are used for the DTV and DVD formats. ! NICAM Nicam (728) stands for Near Instantaneous Companded Audio Multiplex, and is a system initially developed and adopted by the British BBC for Stereo TV transmissions. The system is being used now in most countries in Europe, and may become the standard in stereo TV transmissions. Audio information is digitally coded and transmitted alongside the video information, allowing mono sound reception in receivers not equipped with the NICAM system (down compatibility). A NICAM TV receiver is equipped with a decoder, which converts the coded digital information into two stereo, analog sound channels. GLOSSARY Page 12.16 ! NONLINEARITY The amount, by which the video output signal, when subjected to any load within its capacity, differs from an ideally linear output. The greater the deviance, the greater the distortion of the video signal resulting in both black and white and color problems. All good video-processing devices are designed to contend with nonlinearity. ! NTSC (National Television Standards Committee) Standard of color telecasting used in the United States and Japan, which takes its name from the American committee, which formulated it. The NTSC standard has the advantage of simplicity but there are several major drawbacks to its use such as limited video bandwidth, which affects picture sharpness and faithfulness of colors. ! NYQUIST FREQUENCY The lowest frequency at which a signal may be digitally sampled, in order to allow for faithful reproduction. In most cases it is double the highest frequency available in the sampled signal. ! OVERSAMPLING When a signal is digitally sampled at frequencies much higher than the NYQUIST frequency. When this method is used, filtering the signals is easier and less expensive, although sampling at higher frequencies is more problematic. ! PAL (Phase Alternation Line) The European color TV broadcasting standard featuring 625 lines per frame and 50 frames per second. It has a more complex color encoding system than NTSC, but provides better color fidelity and better resolution. ! PALPLUS A widescreen TV standard (16:9 format) used mainly in Europe for creating a "betterlooking" image on the screen. It employs special technology for color and luminance image enhancement and resembles the HDTV format. It shows as a letterbox on a regular TV. ! PEDESTAL A small DC step within the video signal separating active video from the blanking level which indicates the picture’s black-level. It is used as a reference in a standard video signal for the white level and all the gray levels in between. Only NTSC uses a pedestal. ! PORCH - FRONT/BACK A short period of time, of several microseconds - before and after the sync pulse, that is a part of the blanking period, riding on blanking signal level. The porch can be used for clamping purposes, as it does not carry visible picture information. ! POST-PRODUCTION All the editing work done with the video crude material in the studio after filming. Editing, special effects insertion, image enhancement, and other processes enriching and fine-tuning the production are done in a studio during post-production. GLOSSARY Page 12.17 ! Pr / Pb A color difference signal representing a scaling formula for B-Y and R-Y signals. By using the appropriate formula, 700mVpp of Pr and Pb represent a 100% saturation level in component video. ! RECLOCKING A process used in Serial Digital communication to reduce jitter - usually a result of long cable runs - which has accumulated on the signal. By Reclocking at adequate intervals, cable losses can be completely overcome. In the analog world, Time Base Correction using a TBC performs a similar task. ! RGB (Red/Green/Blue) The basic constituents of a color video signal. By using a color encoder, in conjunction with sync information, a complete composite video signal comprising luminance, Chrominance and sync can be generated. Professional processing equipment always employs RGB and YUV signals for editing and processing. The use of component video, of which RGB is one form, results in superior quality output. ! RISE TIME A parameter indicating the speed and frequency response of an amplifier or of a processing stage in an electronic circuit. Rise Time is the time it takes a signal to change its level from 10% to 90% of the maximum amplitude. The shorter this time, the faster the amplifier. Shorter Rise Time indicates better high frequency response. ! RS-170/170A RS-170 is the American standard used for black and white TV that defines video signal parameters - Sync, Blanking and signal levels. RS-170A is a revision of RS-170, allowing color transmissions and video use. ! RS-232/RS-422 Communication methods between computers and video equipment that are hardware based and software controlled. In the computers, RS-232 is carried through the serial port to another serial port, where the data streams serially between the computer and its peripherals - mouse, plotter, printer, etc. In the computer field there is usually a handshake protocol between the ports that operate bi-directionally. Video equipment can be controlled by either RS-232 or by RS422 system, and as the RS-422 method connects several devices on the same line in parallel in a simple way, it is more popular in the video market. Computer controlled VCRs, editing controllers, switchers and other studio equipment is found in most video studios. In order to successfully link two pieces of hardware, they must use the same communication protocol. ! SAV Start of Active Video. A term used in digital component video to indicate the onset of the active line. ! SCAN CONVERTER A machine that changes the scan rates (sync frequencies and data) of a signal to transform it to another format. If, for example, a VGA signal is to be converted to GLOSSARY Page 12.18 video, a Scan Converter is needed. The operation is done by converting the analog VGA signal to a digital form using an ADC, reading the information into a RAM memory, rescaling the signals and sync information and converting them back to an analog form using a DAC. Scan converters convert both the sync frequencies and the DATA information simultaneously in order to shift all into another format. Scan Converters are also used in order to match specific monitors to signals of other formats. A good example is in the medical field, where data emerging from medical equipment at non-standard rates (like from Ultra Sound scanners or CT scanners) is to be converted to VGA or video formats for processing or recording. The Scan Converters are usually confined for a specific use in order to keep the price low, but there are expensive Scan Converters that convert between a large number of different formats. ! SDI Serial Digital Interface. A format of digital video in serial form, evolving from parallel digital component video, digitized at 4:2:2 ratio. The stream of data is very fast - from 270 Mbits/sec up to 360 Mbits/sec. Other information such as digital AES/EBU audio signals can be embedded in this stream of information. ! SDI CHECK SIGNAL One of the digital test signals used for testing SDI PLL (Phase Locked Loop) and equalizer circuitry. ! SECAM (Sequential Couleur a Memorie) The TV and video standard used in France, Eastern Europe and some Arab countries. The system resembles PAL; however, due to limitations and the complexity of its color encoding, serious video production is almost impossible within the framework of the SECAM system. In countries using the SECAM standard most video production is done using the PAL standard and, prior to transmission, tapes are converted to SECAM. ! SERIAL TO PARALLEL CONVERTER A Deserializer which converts between Serial Digital Video to parallel Digital Video, and is mainly used for interfacing the two digital formats. ! SERRATIONS Serrations are short, positive pulses within the vertical sync which are needed for proper synchronization of the video image on a screen. Loss of serration pulses can result in loss of picture stability, skewing effect and frequently to color loss in the PAL system. ! SIGNAL-TO-NOISE RATIO The ratio, in decibels, of the maximum peak-to-peak voltage of a relevant signal in relation to the voltage of all interfering non-relevant noise signals. In audio, the higher the signal-to-noise ratio, the cleaner the sound; in video, the better the ratio, the less snow resides in the picture. ! SINE X/X A video test signal for testing frequency response. GLOSSARY Page 12.19 ! SKEWING Due to loss or distortion of equalizing pulses and serrations, mainly in high generation videotapes, the upper third of the video picture may flag sidewise or skew. To overcome the problem at the consumer level - his TV is equipped with an AV channel, which, when selected for VCR viewing, changes some time constants in the sync regeneration circuits, allowing viewing without skewing. In professional studios this problem is solved using a TBC. ! SMPTE Society of Motion Picture and Television Engineers. An organization which recommends standards for the film and television industry. ! SMPTE 125M A standard which defines the interface for system M (525/60) digital television and which is based on CCIR 601. This standard is defined for use in television studios for up to 300m distance. It is a Bit-Parallel digital interface for component video signals at 4:2:2 digitization format. ! SMPTE 244M A standard which defines the interface for system M/NTSC (525/60) digital television and which is based on CCIR 601. This standard is defined for use in television studios for up to 300m distance. It is a Bit-Parallel digital interface for composite video signals at 4xFsc sampling frequency. This standard defines the sampling parameters, the relationship between sampling phase and color subcarrier and the digital levels of the video signal. ! SMPTE 259M A standard which describes the serial digital interface for system M (525/60) digital television equipment, operating at either 4:2:2 component video signal or 4Fsc NTSC composite video signal. The standard proposed by the SMPTE is intended for 10 bit digitization schemes. ! s-Video (S-VHS, Hi-8, Y/C) A video system which differs from standard Composite video in several crucial ways. The bandwidth is considerably wider as luminance and Chrominance are separated. This format is widely used for production in semi-professional as well as in many broadcast studios. ! TBC (Time Base Corrector) A device used to rectify the results of distorted sync pulses which are due to mechanical faults (tape transport, tape stretch, etc.). TBCs are also used to synchronize two video sources to allow mixing. TBCs employ one of two technologies. In the past, CCD technology was used to move or alter a video signal in an analog memory chip and was suitable for simple analog synchronization. However, CCDs had very limited memory capabilities. Therefore, Digital TBCs are now common. They usually break down the video signal to its components. This is extremely flexible as it permits storage of a full frame or more in a digital memory device (RAM chips). It operates in full bandwidth with 8 or more bits conversion scheme and is suitable for professional applications. GLOSSARY Page 12.20 ! TDM (Time Division Multiplex) A system intended to combine several signals on one channel by alternately sending packets of each signal in predefined segments of time. ! TEN BIT (10 Bit) An expression used to describe a digital data stream of 10-bit width. A ten-bit digital word can have 1024 steps or values. Digitizing video at 10-bit resolution is acceptable for most broadcast specifications, as the 1024 recovered steps accurately represent the digitized signal. When an 8-bit stream of data is used, only 256 steps are recoverable. ! TERMINATION SWITCH A load device, usually a 75-ohm resistor, connected by a switch to a video transmission line to terminate the line. For a video signal be correctly transmitted without losses, proper impedance matching is essential at the end of the line. In many video-processing devices, a termination switch is therefore included as a standard feature. When the termination switch is in the Hi-Z position, the video signal is not terminated but looped to the next station. The signal can thus be transmitted in parallel through a number of devices. The termination switch terminates the final device. ! TIME CODE A digital code or number inserted into videotape, unseen on the screen, for editing purposes. The time code identifies every frame of the videotape and displays hours, minutes, seconds and frames. For editing purposes it is a must, as each video frame can be addressed individually. There are several methods of inserting and reading time codes such as VITC, LTC and others. ! TP Twisted Pair. A system for transferring high frequency signals on a twisted pair of wires instead of a coax cable. The TP system is used in video and in the computer world as one of the network interconnecting standards. The twisted pair system is essentially a balanced or differential system, where antiphase signals are transmitted on the two wires. Some sophisticated TP systems allow the transfer of several signals simultaneously on the wires, such as video and two audio channels. ! TWO-T (2T) PULSE A sine-squared test pulse for video equipment measurement, with its frequency characteristics covering the bandwidth of the signal. The distortion of this pulse created by the video amplifier or processor is measured in "K" units or factor, and should be as close to zero as possible. This test signal easily detects the transient non-linearity of video devices which results in spurious effects, signal overshoots, ringing etc, due to group delay effects. ! UNDERSCAN The opposite of Overscan, where a video or computer image is shrunk on the screen, leaving black borders around it. Underscan is used to scale large images to screen size and to show on the screen what is happening in the blanking period - at the beginning and end of the lines and the frames. By underscanning some latent problems in the image can be seen and identified for correction. GLOSSARY Page 12.21 ! U, V Color difference signals for PAL Chrominance scaling. They are related by a formula to the B-Y and R-Y levels. ! VECTORSCOPE An electronic test machine for color video systems, for color problem tracing and correction in a TV or video studio. The Vectorscope, displays color vectors and components, as well as the relative position of the Color Burst. See also Waveform Monitor. ! VERTICAL INTERVAL SWITCHING When one video signal replaces another, the switching process may cause 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 tape. 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 video sources are Genlocked to each other. ! VITC Vertical Interval Time Code is the most popular method for inserting and reading time codes on a videotape. The time code is inserted 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 is comprised of a time code generator for inserting the information, and a time code reader to retrieve it. In most cases, both units - the generator and reader - are built into one machine. The VITC system is very reliable, as each and every frame of the video signal has its individual time code. ! VHS Video Home System. A format developed by JVC™ utilizing half-inch tape, which is the most widely used video format. ! 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. ! 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. ! 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 image into several pieces, by converting the GLOSSARY Page 12.22 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. ! 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. ! WAVEFORM MONITOR A test machine similar to an oscilloscope designed to show composite or component video waveforms. Every video line may be selected for display and analysis. The waveform monitor helps fine-tune equipment in a video or TV studio and is very useful in locating problems encountered using complex video equipment. See also Vectorscope. ! WEIGHTED S/N RATIO The ratio of signal to noise level after mathematical manipulation. The mathematical calculation for audio takes into account the frequency response of human hearing and limitations and for video the human eye and the TV/monitor characteristics. This number is usually higher by a few Decibels than the standard S/N ratio (shows better results). ! WHITE BALANCE An electronic process used in video cameras to retain true colors. White balancing is performed prior to recording a specific scene. The camera is pointed at a white object (a wall, for example) and controls on the camera are adjusted until a hairline in the viewfinder is brought to a particular point. This ensures that the tints in the videotape will be natural. White balance, as simple as it seems, can be problematic. Unnatural colors are the result of incorrect white balance. To correct this situation a Chroma corrector is used to restore white balance and normal tints. Most modern cameras nowadays perform automatic white balance control, which eliminates many color aberration problems. ! WIDE SCREEN PROJECTOR A display device that projects a video or computer image on a large screen, mainly for public viewing. The first wide screen projectors had very poor quality and brightness, but today, quality and brightness is very good. The classic wide screen projector has three color tubes - red green and blue, and the image is created on the screen by blending the three colors. One of the most common problems encountered with wide screen projectors was poor alignment of the three tubes. Nowadays, in most high quality projectors, the alignment required to get a good superimposition of the three images on the screen is almost automatic and much easier than in the past. Recently, LCD (Liquid Crystal Display) TFT driven screens, which eliminate alignment problems completely, became the heart of a new series of wide screen projectors. The TFT based projectors offer better price/performance ratios than three tube projectors. Another new generation of projectors is based on DLP / DMD (Digital Micromirrors GLOSSARY Page 12.23 Device) technology in which a semiconductor chip is covered with hundreds of thousands of micro mirrors that change their angle to a beam of light shining on them. This system creates an image that is much more saturated and has more contrast. ! XLR A type of connector, usually of 3 pins (4 and 5 pins are also available), used in professional studio applications. The most familiar use of an XLR connector is in audio where a balanced audio signal uses two of the three pins, and the third carries the common ground. ! YC (Luminance and Chrominance) A complex division of the video signal used in systems such as s-VHS. Due to the intricacy of YC, special processors, switchers, amplifiers, etc. are needed for video editing. ! YUV A video system employing luminance and two Chroma components directly related to the red and blue components. Professional component video systems are used in studios and require special equipment to simultaneously handle the three signals. Interface devices are used to link the various system components - RGB, YC, YUV and YIQ (a system similar to YUV used for NTSC). GLOSSARY Page 12.24