TELEVISION

American rock group that played a prominent role in the emergence of the punknew-wave movement. With Television's first single, Little Johnny Jewel (1975), and much-touted debut album, Marquee Moon (1977), the extended guitar solo found a place in a movement that generally rebelled against intricate musicianship. The principal members were Tom Verlaine (original name Thomas Miller; b. Dec. 13, 1949, Mount Morris, N.J., U.S.), Richard Hell (original name Richard Myers; b. Oct. 2, 1949, Lexington, Ky.), Billy Ficca (b. 1949), Richard Lloyd (b. Oct. 25, 1951, Pittsburgh, Pa.), and Fred Smith (b. April 10, 1948, New York, N.Y.). Guitarist Verlaine (who took his name from the French Symbolist poet Paul Verlaine) and bassist Hell, former boarding-school roommates, formed the Neon Boys with drummer Ficca in New York City in the early 1970s. In 1973 guitarist Lloyd joined them; as Television they helped establish CBGB-OMFUG, a club in New York City's Bowery, as the epicentre of a burgeoning punk scene. Principal songwriter Verlaine delivered his surreal lyrics with an elasticity that stretched from somber declarations to unearthly squeals, but what set Television apart from other punknew-wave groups was the improvisational interplay of Verlaine and Lloyd's guitars, which borrowed from avant-garde jazz and psychedelic rock. Patti Smith, with whom Verlaine wrote poetry and on whose debut single he played, described his guitar playing as the sound of a thousand bluebirds screaming. Released on Elektra, Marquee Moon caused a stir among American critics but, like its more polished follow-up, Adventure (1978), sold much better in Britain. Prior to Marquee Moon, Hell left to form the Heartbreakers (with ex-New York Doll Johnny Thunders), then fronted the Voidoids. Television disbanded in 1978, reuniting briefly in 1992 for an eponymous album and tour. Verlaine also pursued a solo career. an electronic system for transmitting still or moving images and sound to receivers that project a view of the images on a picture tube or screen and re-create the sound. The technology of television has been made possible by a quirk in human vision: images are retained by the retina for a brief time after they strike it. Making use of this phenomenon, bits of a picture are displayed on a television screen fast enough that a viewer sees them assembled as complete pictures. By rapidly changing the pictures on the screen (a rate of between 25 and 30 pictures per second is sufficient), an illusion of motion is created. A television's audiovisual signal begins with the conversion of an image and accompanying sound into an electronic code by a television camera. The resulting electronic signals are usually recorded on tape, and for transmission, or broadcasting, they are impressed on high-frequency radio waves that act as carriers. After transmission by a broadcasting antenna, the carrier waves are picked up by a receiving antenna, which carries them to the television receiver. Inside the receiver the video and audio signals are separated and amplified; they then pass into the picture tube, which re-creates a picture of the original image from the video signals by means of a narrow beam of electrons that bombard the back of a screen coated with a fluorescent compound in a scanning motion. The electrons cause the coating of the screen to light up with the desired brightness in each area of the picture. The electron beam scans across the screen in horizontal lines (525 lines per picture in the United States and 625 in Europe). Each picture is scanned twice, with alternate lines illuminated on each scan. This technique tricks the eye into ignoring the flicker effect caused by displaying successive images too slowly, because it doubles the number of images displayed. Experimentation to create a workable television system began in the late 19th century. In 1884 Paul Nipkow, a German scientist, patented his ideas for a complete television system, the key to which was a rotating disc with holes in a spiral pattern. This provided an effective mechanical means of image scanning that was used until electronic scanning was technically possible. Developments in the period from 1900 to 1920 produced early versions of the picture tube, methods of amplifying an electronic signal, and the theoretical formulation of the electronic-scanning principle; these later became the basis of modern television. In 1926 in England, John L. Baird first demonstrated a true television system by electrically transmitting moving pictures. In 1932 the Radio Corporation of America demonstrated all-electronic television using a camera tube called the iconoscope (patented by Vladimir Zworykin in 1923) and a cathode-ray tube in the receiver. By the early 1950s a colour-television system had been developed based on the idea of separating the black-and-white and colour signals. The black-and-white signal gives a high level of detail and can be received by all television sets. The colour signal is projected into the clear areas of the black-and-white signal, in much the same way that one fills colour into the outline of a child's colouring book. This system also has the advantage of being compatible with black-and-white sets, which can still get a good picture from the same combined signal. Since the 1950s the improvements in colour-television technology have resulted in larger picture tubes with clearer images. Cable television systems for distributing signals over coaxial cables give improved reception and additional viewing channels. In addition, a device for projecting television onto a large screen became available in the late 1970s. Machines that can record television signals for later playback or play recorded material from videotape cassettes (especially videocassette recorders, or VCRs) or videodiscs have also become common. By the late 20th century, efforts were under way to develop high-definition television, or HDTV; this term denotes any system yielding significantly greater picture resolution than that of the ordinary 525-line screen. Initial efforts centred on increasing the density of picture lines to more than 1,000, but these were overtaken in the 1990s by the adaptation of digital technology to television transmission and reception. Conventional television transmits signals in analog formi.e., as a series of waves that can reproduce the original images and sounds captured by cameras and microphones; these waves are then decoded and amplified within the television set. Digital HDTV systems, by contrast, transmit pictures and sounds in the form of digital datai.e., in the 0's and 1's of the binary computer code. This numerical data is broadcast using the same high radio frequencies that carry analog waves, and computer processors within the digital television set then decode the data. Digital HDTV can provide sharper, clearer pictures and sound with very little interference or other imperfections. Perhaps more importantly, digital television sets would potentially be able to send, store, and manipulate images as well as receive them, thereby merging the functions of the television set with those of a small computer. Additional reading Donald G. Fink and David M. Lutyens, The Physics of Television (1960), is a nontechnical treatment of television principles. Milton S. Kiver and Milton Kaufman, Television Electronics: Theory and Servicing, 8th ed. (1983); Bernard Grob, Basic Television and Video Systems, 5th ed. (1984); and K. Blair Benson (ed.), Television Engineering Handbook (1986), are comprehensive treatments. Technical aspects are also covered in Gerald Millerson, The Technique of Television Production, 12th ed. (1990); and Herbert Zettl, Television Production Handbook, 5th ed. (1992). Cable technology and the cable industry are described in William Grant, Cable Television (1983); Timothy Hollins, Beyond Broadcasting: Into the Cable Age (1984), on experiences in Canada, the United States, and Great Britain; and Thomas F. Baldwin and D. Stevens McVoy, Cable Communication, 2nd ed. (1988). Direct-broadcast satellite television is covered by Frank Baylin and Brent Gale, Satellites Today: The Guide to Satellite Television, 2nd ed. (1986). Stan Prentiss, HDTV: High-Definition Television (1990), addresses the technical aspects of and involvement by the government and the television industry in this emerging technology. Thornton Howard Bridgewater Donald G. Fink The Editors of the Encyclopdia Britannica Compatible colour television Basic principlesUnited States system The technique of compatible colour television utilizes two transmissions. One of these, the luminance (brightness) transmission, employs methods essentially identical to those of the monochrome television system. The second, the chrominance (colour) transmission, has virtually no effect on monochrome receivers. When used with the luminance transmission in a colour receiver, however, it produces an image in full colour. The luminancechrominance method of representing colour values is one of several alternative ways in which coloured light may be analyzed and synthesized. This method is particularly appropriate in a television system since it produces a compatible signal that can serve both black-and-white and colour receivers by the same broadcast. Historically, compatibility was of great importance because it allowed colour transmissions to be introduced without obsolescence of the many millions of monochrome receivers in use. In a larger sense, the luminancechrominance method of colour transmission is advantageous because it utilizes the limited channels of the radio spectrum more efficiently than other colour transmission methods. To create the luminancechrominance values, it is necessary (in the present state of technology) first to analyze each colour in the scene into primary colours. Coloured light may thus be analyzed by passing the light through three coloured filters, typically red, green, and blue. The amounts of light passing through each filter, plus a description of the colour transmission properties of the filters, serve uniquely to characterize the coloured light. The fact that virtually the whole range of colours may be synthesized from only three primary colours is essentially a description of the process by which the eye and mind of the observer recognize and distinguish colours. Like visual persistence, this is a fortunate property of vision, since it permits a simple three-part specification to represent any of the 10,000 or more colours and brightnesses that may be distinguished by human vision. If vision were dependent on the energy versus wavelength relationship (the physical method of specification), it is doubtful if colour reproduction could be incorporated in any mass-communication system. By transforming the primary-colour values, it is possible to specify any coloured light by three other numbers: (1) its luminance (brightness or brilliance); (2) its hue (the redness, orangeness, blueness, or greenness, etc., of the light); and (3) its saturation (its vivid versus pastel quality). If the intended luminance value of each point in the scanning pattern is transmitted by the methods of the monochrome television system, it is only necessary to transmit, via an additional two-valued signal, supplementary information giving the hue and saturation of the intended colour at the respective points in the scanning pattern. Chrominance, defined as that part of the colour specification remaining when the luminance is removed, represents two independent quantities, hue and saturation. In the colour television system of the United States, the chrominance signal is an alternating current of precisely specified frequency (3.579545 0.000010 megahertz), the precision permitting its accurate recovery at the receiver even in the presence of severe noise or interference. Any change in the amplitude of its alternations at any instant corresponds to a change in the saturation of the colours being passed over by the scanning spot at that instant, whereas a shift in time of its alternations (a change in the phase angle of the alternations) similarly corresponds to a shift in the hue. The colour information in the European (PAL and SECAM) systems is carried on a chrominance signal frequency of 4.43+ megahertz. In the United States system, as the different saturations and hues along each scanning line are successively uncovered by scanning in the camera, the amplitude and phase, respectively, of the chrominance signal change accordingly. The chrominance signal is thereby simultaneously modulated in amplitude and in phase. This doubly modulated signal is imposed on the picture signal carrier current, along with the luminance signal. Figure 13: Allocation channel for compatible colour transmission in the United States. Figure 11: Allocation of television channel for monochrome broadcasting in the United States. The television channel, when occupied by such a compatible colour transmission, appears as shown in Figure 13 (compare this with the channel when occupied by a black-and-white transmission, Figure 11). The chrominance signal takes the form of a subcarrier located precisely 3.579545 megahertz from the picture carrier frequency. The picture carrier is thus simultaneously amplitude-modulated by the luminance signal to represent changes in the intended luminance, and by the chrominance subcarrier that, in turn, is amplitude-modulated to represent changes in the intended saturation and phase-modulated to represent changes in the intended hue. When compatible colour transmissions are received on a monochrome receiver, the receiver treats the chrominance subcarrier as though it were a part of the intended monochrome transmission. If steps were not taken to prevent it, the subcarrier would produce interference in the form of a fine dot pattern. The dot pattern, fortunately, can be rendered almost invisible in monochrome reception by deriving the timing of the scanning motions directly from the source that establishes the chrominance subcarrier itself. The dot pattern of interference from the chrominance signal, therefore, can be made to have opposite effects on successive scannings of the pattern; that is, a point brightened by the dot interference on one line scan is darkened an equal amount on the next scan of that line, and the net effect of the interference, integrated in the eye over successive scans, is virtually zero. Thus, the monochrome receiver, in effect, ignores the chrominance component of the transmission. It deals with the luminance signal in the conventional manner, producing from it a monochrome image. This monochrome rendition, incidentally, is not a compromise; it is essentially identical to the image that would be produced by a monochrome television system viewing the same scene. The channel for colour transmissions, when used by colour receivers, would appear to be affected by mutual interference between the luminance and chrominance components, since these occupy a portion of the channel in common. Such interference is avoided by the fact that the chrominance subcarrier component is rigidly timed to the scanning motions. The luminance signal, as it occupies the channel, is actually concentrated in a multitude of small spectrum segments, by virtue of the periodicities associated with the scanning process. Between these segments are empty channel spaces of approximately equal size. The chrominance signal, arising from the same scanning process, is similarly concentrated. Hence it is possible to place the chrominance channel segments within the empty spaces between the luminance segments, provided that the two sets of segments have a precisely fixed frequency relationship. The necessary relationship is provided by the direct control by the subcarrier of the timing of the scanning motions. This intersegmentation is referred to as frequency interlacing. It is one of the fundamentals of the compatible colour system. Without frequency interlacing, the superposition of colour information on a channel originally devised for monochrome transmissions would not be feasible. Figure 13: Allocation channel for compatible colour transmission in the United States. When a colour receiver is tuned to the transmission represented in Figure 13, the picture signal is recovered in a video detector in the usual manner. An amplifier stage, tuned to the 3.58-megahertz chrominance frequency, then selects the chrominance from the picture signal and passes it to a detector that recovers independently the amplitude-modulated and phase-modulated components. European colour systems The U.S. colour system has been adopted by Canada, Mexico, Japan, and several other countries. In Europe two alternative systems have been developed and introduced. The PAL (phase alternation line) system has been adopted in the United Kingdom and most of the countries on the Continent. France, however, has adopted the SECAM (systme lectronique couleur avec mmoire) system. The PAL and SECAM systems embody the same principles as the U.S. system, including matters affecting compatibility and the use of a separate signal to carry the colour information at low detail superimposed on the high-detail luminance signal. The European systems were developed, in fact, to improve on the performance of the U.S. system in only one area, the constancy of the hue of the reproduced images. It has been pointed out that the hue information in the U.S. system is carried by changes in the phase angle of the chrominance signal and that these phase changes are recovered in the receiver by synchronous detection. The transmission of the phase information, particularly in the early stages of colour broadcasting in the United States, was subject to incidental errors arising in broadcasting stations and network connections. Errors are also caused by reflections of the broadcast signals by buildings and other structures in the vicinity of the receiving antenna. In recent years, transmission and reception of hue information has become substantially more accurate in the United States through care in broadcasting and networking, as well as by automatic hue-control circuits in receivers. The PAL and SECAM systems are inherently less affected by phase errors. In the PAL and SECAM systems, the nominal value of the chrominance signal is 4.43+ megahertz, a frequency that is derived from and hence accurately synchronized with the frame-scanning and line-scanning rates. This chrominance signal is accommodated within the six-megahertz range of the fully transmitted side band. By virtue of its synchronism with the line and frame scanning rates, its frequency components are interleaved with those of the luminance signal, so that the chrominance information does not affect reception of colour broadcasts by black-and-white receivers. Principles of picture transmission and reception Basic factors The quality and quantity of television service are limited fundamentally by the rate at which it is feasible to transmit the picture information over the television channel. In modern practice the televised image must be capable of being dissected, within a few hundredths of a second, into more than 100,000 picture elements. This implies that the electrical impulses corresponding to the picture elements must pass through the channel at a rate as high as several million per second. Moreover, since the picture content may vary, from frame to frame, from simple close-up shots having little fine detail to comprehensive distant scenes in which the limiting detail of the system comes into play, the actual rate of transmitting the picture information varies from time to time, from a few impulses per second to several million per second. The television channel must be capable, therefore, of handling information over a continuous band of frequencies several million cycles wide. This is testimony to the extraordinary comprehension of the human sense of sight. Hearing is comparatively crude. The ear is satisfied by sound produced by impulses that can be carried over a channel only 10,000 cycles wide. In the United States, the television channel occupies a width of six megacycles (6,000,000 hertz, or cycles per second) in the radio spectrum. This is 600 times as wide as the channel used by each standard sound broadcasting station. In fact, each television station uses nearly six times as much spectrum space as all the commercial amplitude-modulation (AM) sound broadcasting channels combined. Since each television station must occupy so much spectrum space, few channels are available in a given locality. Moreover, the quantity of service is in conflict with the quality of reproduction. If the detail of the television image is to be increased, other parameters of the transmission being unchanged, the channel width must be increased proportionately, and this decreases the number of channels that can be accommodated in the spectrum. This fundamental conflict between quality of transmission and number of available channels dictates that the quality of reproduction shall just satisfy the typical viewer under normal viewing conditions. Any excess of performance beyond this ultimately would result in a restriction of program choice. Flicker The first requirement to be met in image analysis is that the reproduced picture shall not flicker, since flicker induces severe visual fatigue. Flicker becomes more evident as the brightness of the picture increases. If flicker is to be unobjectionable at brightness suitable for home viewing during daylight as well as evening hours (25 to 100 footlamberts), the successive illuminations of the picture screen should occur no fewer than 50 times per second. This is approximately twice the rate of picture repetition needed for smooth reproduction of motion. To avoid flicker, therefore, twice as much channel space is needed as would suffice to depict motion. The same disparity occurs in motion-picture practice, in which satisfactory performance with respect to flicker requires twice as much film as is necessary for smooth simulation of motion. A way around this difficulty has been found, in motion pictures as well as in television, by projecting each picture twice. In motion pictures, the projector interposes a shutter briefly between film and lens while a single frame of the film is being projected. In television, each image is analyzed and synthesized in two sets of spaced lines, one of which fits successively within the spaces of the other. Thus the picture area is illuminated twice during each complete picture transmission, although each line in the image is present only once during that time. This technique is feasible because the eye is comparatively insensitive to flicker when the variation of light is confined to a small part of the field of view. Hence flicker of the individual lines is not evident. If the eye did not have this fortunate property, a television channel would have to occupy about twice as much spectrum space as it now does. It is thus possible to avoid flicker and simulate rapid motion by a picture rate of about 25 per second, with two screen illuminations per picture. The precise value of the picture-repetition rate used in a given region has been chosen by reference to the electric power frequency that predominates in that region. In Europe, where 50-hertz power is the rule, the television picture rate is 25 per second (50 screen illuminations per second). In North America the picture rate is 30 per second (60 screen illuminations per second) to match the 60-hertz power that predominates there. The higher picture-transmission rate of North America allows the pictures there to be about five times as bright as those in Europe for the same susceptibility to flicker, but this advantage is offset by a 20 percent reduction in picture detail for equal utilization of the channel.