Technology of television
Encyclopedia
The technology of television has changed since its early days using a mechanical system invented by Paul Gottlieb Nipkow
in 1884.
The elements of a simple broadcast
television system are:
Practical television systems include equipment for selecting different image sources, mixing images from several sources at once, insertion of pre-recorded video signals, synchronizing signals from many sources, and direct image generation by computer
for such purposes as station identification. The facility for housing such equipment, as well as providing space for stages, sets, offices, etc., is called a television studio
, and may be located many miles from the transmitter
. Communication from the studio to the transmitter
is accomplished via a dedicated cable or radio
system.
Television signals were originally transmitted exclusively via land-based transmitters. The quality of reception varied greatly, dependent in large part on the location and type of receiving antenna. This led to the proliferation of large rooftop antennas to improve reception in the 1960s, replacing set-top dipole
or "rabbit ears" antennas, which however remained popular. Antenna rotors, set-top controlled servo motors
to which the mast of the antenna is mounted, to enable rotating the antenna such that it points to the desired transmitter, would also become popular.
In most cities today, cable television
providers deliver signals over coaxial
or fiber-optic
cables for a fee. Signals can also be delivered by radio
from satellites
in geosynchronous orbit
and received by parabolic dish antennas
, which are comparatively large for analog
signals, but much smaller for digital
. Like cable providers, satellite television
providers also require a fee, often less than cable systems. The affordability and convenience of digital satellite reception has led to the proliferation of small dish antennas outside many houses and apartments.
Digital systems may be inserted anywhere in the chain to provide better image transmission quality, reduction in transmission bandwidth, special effects, or security of transmission from reception by non-subscribers. A home today might have the choice of receiving analog or HDTV over the air, analog or digital cable with HDTV from a cable television
company over coaxial cable
, or even from the phone company over fiber optic
lines. On the road, television can be received by pocket sized televisions, recorded on tape or digital media players, or played back on wireless phones (mobile or "cell" phones)
over a high-speed or "broadband" internet connection
.
Thanks to the advances in display technology, there are now several kinds of video displays used in modern TV sets:
Each has its pros and cons. Flat panel LCD and plasma displays have a wide viewing angle (around 178 degrees) so they may best suited for a home theatre with a wide seating arrangement. Rear projection screens do not perform well in daylight
or well-lit rooms and so are only suited to darker viewing areas.
is the number of pixels of one row on a given screen. Before the year 2000 horizontal lines of resolution was the standard method of measurement for analog video. For example, a VHS VCR might be described as having 250 lines of resolution as measured across a circle circumscribed in the center of the screen (approximately 440 pixels edge-to-edge).
A typical resolution of 720×480 and 720x576 means that the television display has 720 pixels across and 480 or 576 pixels on the vertical axis. The higher the resolution on a specified display the sharper the image. Contrast ratio
is a measurement of the range between the lightest and darkest points on the screen.
The higher the contrast ratio, the better looking picture there is in terms of richness, deepness, and shadow
detail. The brightness
of a picture measures how vibrant and impacting the colors are. Measured in
equivalent to the amount of candles required to power the image
.
On the other hand, the so-called brightness and contrast adjustment controls on televisions and monitors are traditionally used to control different aspects of the picture display. The brightness control shifts the black level, affecting the image intensity or brightness, while the contrast control adjusts the contrast range of the image.
initially used Band I VHF at 45 MHz, this frequency is (in the UK) no longer in use for this purpose. Band II is used for FM radio transmissions. Higher frequencies behave more like light and do not penetrate buildings or travel around obstructions well enough to be used in a conventional broadcast TV system, so they are generally only used for MMDS and satellite television
, which uses frequencies from 2 to 12 GHz. TV systems in most countries relay the video as an AM (amplitude-modulation) signal and the sound as an FM (frequency-modulation) signal. An exception is France
, where the sound is AM.
refers to the ratio of the horizontal to vertical measurements of a television's picture. Mechanically scanned television as first demonstrated by John Logie Baird
in 1926 used a 7:3 vertical aspect ratio, oriented for the head and shoulders of a single person in close-up.
Most of the early electronic TV systems, from the mid-1930s onward, shared the same aspect ratio
of 4:3 which was chosen to match the Academy Ratio
used in cinema films at the time. This ratio was also square enough to be conveniently viewed on round cathode-ray tubes
(CRTs), which were all that could be produced given the manufacturing
technology
of the time. (Today's CRT technology allows the manufacture of much wider tubes, and the flat-screen technologies which are becoming steadily more popular have no technical aspect ratio limitations at all.) The BBC
's television service used a more squarish 5:4 ratio from 1936 to 3 April 1950, when it too switched to a 4:3 ratio. This did not present significant problems, as most sets at the time used round tubes which were easily adjusted to the 4:3 ratio when the transmissions changed.
In the early 1950s, movie studio
s moved towards widescreen
aspect ratios such as CinemaScope
in an effort to distance their product from television. Although this was initially just a gimmick
, widescreen is still the format of choice today and 4:3 aspect ratio movies are rare.
Yet the various television systems were not originally designed to be compatible with film at all. Traditional, narrow-screen movies are projected onto a television camera either so that the top of the screens line up to show facial features, or, for films with subtitles, the bottoms. What this means is that filmed newspapers or long captions filling the screen for explanation are cut off at each end. Similarly, while the frame rate of sound films is 24 per second, the screen scanning rate of the NTSC is 29.97 Hz
(per second), which requires a complex scanning schedule. That of PAL and SECAM are 50 Hz, which means that films are shortened (and the sound is offkey) by scanning each frame twice for 25 per second.
The switch to digital television
systems has been used as an opportunity to change the standard television picture format from the old ratio of 4:3 (1.33:1) to an aspect ratio of 16:9 (approximately 1.78:1). This enables TV to get closer to the aspect ratio of modern widescreen movies
, which range from 1.66:1 through 1.85:1 to 2.35:1. There are two methods for transporting widescreen content, the most common of which uses what is called anamorphic widescreen format. This format is very similar to the technique used to fit a widescreen movie frame inside a 1.33:1 35 mm film frame. The image is compressed horizontally when recorded, then expanded again when played back. The anamorphic widescreen 16:9 format was first introduced via European PALplus
television broadcasts and then later on "widescreen" Laser Discs and DVD
s; the ATSC HDTV
system uses straight widescreen format, no horizontal compression or expansion is used.
Recently "widescreen" has spread from television to computing where both desktop
and laptop
computers are commonly equipped with widescreen displays. There are some complaints about distortions of movie picture ratio due to some DVD playback software not taking account of aspect ratios; but this may subside as the DVD playback software matures. Furthermore, computer and laptop widescreen displays are in the 16:10 aspect ratio both physically in size and in pixel counts, and not in 16:9 of consumer televisions, leading to further complexity. This was a result of widescreen computer display engineers' assumption that people viewing 16:9 content on their computer would prefer that an area of the screen be reserved for playback controls, subtitles or their Taskbar, as opposed to viewing content full-screen.
is not without difficulties, and can present a considerable problem.
Displaying a widescreen aspect (rectangular) image on a conventional aspect (square or 4:3) display can be shown:
A conventional aspect (square or 4:3) image on a widescreen aspect (rectangular with longer horizon) display can be shown:
A common compromise is to shoot or create material at an aspect ratio of 14:9, and to lose some image at each side for 4:3 presentation, and some image at top and bottom for 16:9 presentation. In recent years, the cinematographic process known as Super 35 (championed by James Cameron
) has been used to film a number of major movies such as Titanic
, Legally Blonde
, Austin Powers
, and Crouching Tiger, Hidden Dragon
(see also: Films shot in Super 35). This process results in a camera-negative which can then be used to create both wide-screen theatrical prints, and standard "full screen" releases for television/VHS/DVD which avoid the need for either "letterbox
ing" or the severe loss of information caused by conventional "pan-and-scan" cropping.
standard televisions with analog-only tuners went dark unless fitted with a digital ATSC tuner
, and the spectrum previously occupied by those analog channels was auctioned off by the United States' Federal Communications Commission for other uses.
and SECAM
are expected not to be broadcast in Europe and Eurasia by the mid-2020s. PAL-M may have a similar decommissioning timeline.
The European Union
has recommended its members to close down analogue terrestrial television by 2012. Luxembourg and the Netherlands already completed their closedowns in 2006, and Finland and Sweden closed down their analogue broadcasts in 2007.
Britain started its digital switch in October 2007. At 2AM on Wednesday 17 October 2007, the BBC2 transmitter covering the Whitehaven and Copeland areas (NW England) was disabled. The remaining four analogue channels ceased broadcasting shortly after. The original five channels are now available only in digital form, alongside approximately 15 additional free-to-air channels.
and a turntable
.
Paul Gottlieb Nipkow
Paul Julius Gottlieb Nipkow was a German technician and inventor.-Beginnings:Nipkow was a German of born in Lauenburg in Pomerania. While at school in Neustadt , West Prussia, Nipkow experimented in telephony and the transmission of moving pictures. After graduation, he went to Berlin in order to...
in 1884.
Elements of a television system
Broadcasting
Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
television system are:
- An image source. This is the electrical signal representing the visual image, and may be from a professional video cameraProfessional video cameraA professional video camera is a high-end device for creating electronic moving images...
in the case of live televisionLive televisionLive television refers to a television production broadcast in real-time, as events happen, in the present. From the early days of television until about 1958, live television was used heavily, except for filmed shows such as I Love Lucy and Gunsmoke. Video tape did not exist until 1957...
, a video tape recorderVideo tape recorderA video tape recorder is a tape recorder that can record video material, usually on a magnetic tape. VTRs originated as individual tape reels, serving as a replacement for motion picture film stock and making recording for television applications cheaper and quicker. An improved form included the...
for playback of recorded images, or telecineTelecineTelecine is transferring motion picture film into video and is performed in a color suite. The term is also used to refer to the equipment used in the post-production process....
with a flying spot scannerFlying spot scannerA flying-spot scanner uses a scanning source of a spot of light, such as a high-resolution, high-light-output, low-persistence Cathode Ray Tube , to scan an image, usually from motion picture film or a slide...
for the transfer of motion pictures to video). - A sound source. This is an electrical signal from a microphoneMicrophoneA microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
or from the audio output of a video tape recorderVideo tape recorderA video tape recorder is a tape recorder that can record video material, usually on a magnetic tape. VTRs originated as individual tape reels, serving as a replacement for motion picture film stock and making recording for television applications cheaper and quicker. An improved form included the...
. - A transmitterTransmitterIn electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
, which generates radioRadioRadio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
signals (radioRadioRadio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
waves) and encodes them with picture and sound information. - A television antennaTelevision antennaA television antenna, or TV aerial, is an antenna specifically designed for the reception of over the air broadcast television signals, which are transmitted at frequencies from about 41 to 250 MHz in the VHF band, and 470 to 960 MHz in the UHF band in different countries...
coupled to the output of the transmitterTransmitterIn electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
for broadcastingBroadcastingBroadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
the encoded signals. - A [television antenna to receive the broadcastBroadcastingBroadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
signals. - A receiver (also called a tuner), which decodes the picture and sound information from the broadcastBroadcastingBroadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
signals, and whose input is coupled to the antenna of the television setTelevision setA television set is a device that combines a tuner, display, and speakers for the purpose of viewing television. Television sets became a popular consumer product after the Second World War, using vacuum tubes and cathode ray tube displays...
. - A display deviceDisplay deviceA display device is an output device for presentation of information in visual or tactile form...
, which turns the electrical signals into visual images. - An audioSoundSound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
amplifierAmplifierGenerally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
and loudspeakerLoudspeakerA loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
, which turns electrical signals into sound waves (speech, music, and other sounds) to accompany the images.
Practical television systems include equipment for selecting different image sources, mixing images from several sources at once, insertion of pre-recorded video signals, synchronizing signals from many sources, and direct image generation by computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
for such purposes as station identification. The facility for housing such equipment, as well as providing space for stages, sets, offices, etc., is called a television studio
Television studio
A television studio is an installation in which a video productions take place, either for the recording of live television to video tape, or for the acquisition of raw footage for post-production. The design of a studio is similar to, and derived from, movie studios, with a few amendments for the...
, and may be located many miles from the transmitter
Transmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
. Communication from the studio to the transmitter
Transmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
is accomplished via a dedicated cable or radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
system.
Television signals were originally transmitted exclusively via land-based transmitters. The quality of reception varied greatly, dependent in large part on the location and type of receiving antenna. This led to the proliferation of large rooftop antennas to improve reception in the 1960s, replacing set-top dipole
Dipole antenna
A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other , with a small space between them. The radio frequency voltage is applied to the antenna at...
or "rabbit ears" antennas, which however remained popular. Antenna rotors, set-top controlled servo motors
Servomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
to which the mast of the antenna is mounted, to enable rotating the antenna such that it points to the desired transmitter, would also become popular.
In most cities today, cable television
Cable television
Cable television is a system of providing television programs to consumers via radio frequency signals transmitted to televisions through coaxial cables or digital light pulses through fixed optical fibers located on the subscriber's property, much like the over-the-air method used in traditional...
providers deliver signals over coaxial
Coaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
or fiber-optic
Fiber-optic communication
Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information...
cables for a fee. Signals can also be delivered by radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
from satellites
Satellite television
Satellite television is television programming delivered by the means of communications satellite and received by an outdoor antenna, usually a parabolic mirror generally referred to as a satellite dish, and as far as household usage is concerned, a satellite receiver either in the form of an...
in geosynchronous orbit
Geosynchronous orbit
A geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...
and received by parabolic dish antennas
Parabolic antenna
A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish...
, which are comparatively large for analog
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
signals, but much smaller for digital
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
. Like cable providers, satellite television
Satellite television
Satellite television is television programming delivered by the means of communications satellite and received by an outdoor antenna, usually a parabolic mirror generally referred to as a satellite dish, and as far as household usage is concerned, a satellite receiver either in the form of an...
providers also require a fee, often less than cable systems. The affordability and convenience of digital satellite reception has led to the proliferation of small dish antennas outside many houses and apartments.
Digital systems may be inserted anywhere in the chain to provide better image transmission quality, reduction in transmission bandwidth, special effects, or security of transmission from reception by non-subscribers. A home today might have the choice of receiving analog or HDTV over the air, analog or digital cable with HDTV from a cable television
Cable television
Cable television is a system of providing television programs to consumers via radio frequency signals transmitted to televisions through coaxial cables or digital light pulses through fixed optical fibers located on the subscriber's property, much like the over-the-air method used in traditional...
company over coaxial cable
Coaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
, or even from the phone company over fiber optic
Fiber-optic communication
Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information...
lines. On the road, television can be received by pocket sized televisions, recorded on tape or digital media players, or played back on wireless phones (mobile or "cell" phones)
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
over a high-speed or "broadband" internet connection
Broadband Internet access
Broadband Internet access, often shortened to just "broadband", is a high data rate, low-latency connection to the Internet— typically contrasted with dial-up access using a 56 kbit/s modem or satellite Internet with inherently high latency....
.
Display technology
- CRT (cathode-ray tube): The most common screens were direct-view CRTs for up to roughly 100 cm (40 inch) (in 4:3 ratio) and 115 cm (45 inch) (in 16:9 ratio) diagonalDiagonalA diagonal is a line joining two nonconsecutive vertices of a polygon or polyhedron. Informally, any sloping line is called diagonal. The word "diagonal" derives from the Greek διαγώνιος , from dia- and gonia ; it was used by both Strabo and Euclid to refer to a line connecting two vertices of a...
s. These are the least expensive, and are a refined technology that can still provide the best overall picture quality value. As they do not have a fixed native resolutionNative resolutionThe native resolution of a LCD, LCoS or other flat panel display refers to its single fixed resolution. As an LCD display consists of a fixed raster, it cannot change resolution to match the signal being displayed as a CRT monitor can, meaning that optimal display quality can be reached only when...
, they are capable of displaying sources with different resolutions at the best possible image quality. The frame rateFrame rateFrame rate is the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...
or refresh rate of a typical NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
format CRT TV is 29.97 Hz, and for the PALPALPAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
format, 25 Hz, both are scanned with two fields per frame in an interlaced fashion. A typical NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
broadcast signal's visible portion has an equivalent resolution of about 640x480 pixels. It actually could be slightly higher than that, but the vertical blanking intervalVertical blanking intervalThe vertical blanking interval , also known as the vertical interval or VBLANK, is the time difference between the last line of one frame or field of a raster display, and the beginning of the first line of the next frame. It is present in analog television, VGA, DVI and other signals. During the...
(VBI), allows other signals to be carried along with the broadcast. - Rear ProjectionRear-projection televisionRear-projection television or RPTV is a type of large-screen television display technology. Up until the mid-2000s, most of the relatively affordable consumer large screen TVs up to used rear-projection technology...
(RPTV): Most very large screen TVs (up to 254 cm (100 inch) and beyond) use projectionVideo projectorA video projector is an image projector that receives a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright light to project the image, and most modern ones can correct any curves, blurriness, and other...
technology. Three types of projection systems are used in projection TVs: CRT-based, LCDLiquid crystal displayA liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
-based, and DLP (reflective micromirror chip) -based, D-ILA and LCOS-based. Projection television has been commercially available since the 1970s, but at that time could not match the image sharpness of the CRT; current models are vastly improved, and offer a cost-effective large-screen display.- A variation is a video projectorVideo projectorA video projector is an image projector that receives a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright light to project the image, and most modern ones can correct any curves, blurriness, and other...
, using similar technology, which projects onto a screenProjection screenA projection screen is an installation consisting of a surface and a support structure used for displaying a projected image for the view of an audience. Projection screens may be permanently installed, as in a movie theater; painted on the wall; or semi-permanent or mobile, as in a conference room...
. This is often referred to as "front projection".
- A variation is a video projector
- Flat panel displayFlat panel displayFlat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
(LCDLiquid crystal displayA liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
or plasmaPlasma displayA plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
): Modern advances have brought flat panelsFlat panel displayFlat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
to TV that use active matrixActive-matrix liquid crystal displayAn active matrix liquid crystal display is a type of flat panel display, currently the overwhelming choice of notebook computer manufacturers, due to low weight, very good image quality, wide color gamut and response time...
LCD or plasma display technology. Flat panel LCDs and plasma displays are as little as 25.4 mm (1 inch) thick and can be hung on a wall like a picture or put over a pedestalPedestalPedestal is a term generally applied to the support of a statue or a vase....
. Some models can also be used as computer monitors. - LED technology has become one of the choices for outdoor video and stadium uses, since the advent of bright LEDsLight-emitting diodeA light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
and driver circuits. LEDs enable scalable ultra-large flat panel video displays that other technologies are currently not able to match in performance.
Each has its pros and cons. Flat panel LCD and plasma displays have a wide viewing angle (around 178 degrees) so they may best suited for a home theatre with a wide seating arrangement. Rear projection screens do not perform well in daylight
Daylight
Daylight or the light of day is the combination of all direct and indirect sunlight outdoors during the daytime. This includes direct sunlight, diffuse sky radiation, and both of these reflected from the Earth and terrestrial objects. Sunlight scattered or reflected from objects in outer space is...
or well-lit rooms and so are only suited to darker viewing areas.
Terminology for televisions
Pixel resolutionDisplay resolution
The display resolution of a digital television or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by all different factors in cathode ray tube , flat panel or projection...
is the number of pixels of one row on a given screen. Before the year 2000 horizontal lines of resolution was the standard method of measurement for analog video. For example, a VHS VCR might be described as having 250 lines of resolution as measured across a circle circumscribed in the center of the screen (approximately 440 pixels edge-to-edge).
A typical resolution of 720×480 and 720x576 means that the television display has 720 pixels across and 480 or 576 pixels on the vertical axis. The higher the resolution on a specified display the sharper the image. Contrast ratio
Ratio
In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is...
is a measurement of the range between the lightest and darkest points on the screen.
The higher the contrast ratio, the better looking picture there is in terms of richness, deepness, and shadow
Shadow
A shadow is an area where direct light from a light source cannot reach due to obstruction by an object. It occupies all of the space behind an opaque object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the...
detail. The brightness
Brightness
Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target...
of a picture measures how vibrant and impacting the colors are. Measured in
equivalent to the amount of candles required to power the imageImage
An image is an artifact, for example a two-dimensional picture, that has a similar appearance to some subject—usually a physical object or a person.-Characteristics:...
.
On the other hand, the so-called brightness and contrast adjustment controls on televisions and monitors are traditionally used to control different aspects of the picture display. The brightness control shifts the black level, affecting the image intensity or brightness, while the contrast control adjusts the contrast range of the image.
Transmission band
There are various bands on which televisions operate depending upon the country. The VHF and UHF signals in bands III to V are generally used. Lower frequencies do not have enough bandwidth available for television. Although the BBCBBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
initially used Band I VHF at 45 MHz, this frequency is (in the UK) no longer in use for this purpose. Band II is used for FM radio transmissions. Higher frequencies behave more like light and do not penetrate buildings or travel around obstructions well enough to be used in a conventional broadcast TV system, so they are generally only used for MMDS and satellite television
Satellite television
Satellite television is television programming delivered by the means of communications satellite and received by an outdoor antenna, usually a parabolic mirror generally referred to as a satellite dish, and as far as household usage is concerned, a satellite receiver either in the form of an...
, which uses frequencies from 2 to 12 GHz. TV systems in most countries relay the video as an AM (amplitude-modulation) signal and the sound as an FM (frequency-modulation) signal. An exception is France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, where the sound is AM.
Aspect ratios
Aspect ratioAspect ratio (image)
The aspect ratio of an image is the ratio of the width of the image to its height, expressed as two numbers separated by a colon. That is, for an x:y aspect ratio, no matter how big or small the image is, if the width is divided into x units of equal length and the height is measured using this...
refers to the ratio of the horizontal to vertical measurements of a television's picture. Mechanically scanned television as first demonstrated by John Logie Baird
John Logie Baird
John Logie Baird FRSE was a Scottish engineer and inventor of the world's first practical, publicly demonstrated television system, and also the world's first fully electronic colour television tube...
in 1926 used a 7:3 vertical aspect ratio, oriented for the head and shoulders of a single person in close-up.
Most of the early electronic TV systems, from the mid-1930s onward, shared the same aspect ratio
Aspect ratio (image)
The aspect ratio of an image is the ratio of the width of the image to its height, expressed as two numbers separated by a colon. That is, for an x:y aspect ratio, no matter how big or small the image is, if the width is divided into x units of equal length and the height is measured using this...
of 4:3 which was chosen to match the Academy Ratio
Academy ratio
The Academy ratio of 1.375:1 is an aspect ratio of a frame of 35mm film when used with 4-perf pulldown. It was standardized by the Academy of Motion Picture Arts and Sciences as the standard film aspect ratio in 1932, although similar-sized ratios were used as early as 1928.The Academy ratio is...
used in cinema films at the time. This ratio was also square enough to be conveniently viewed on round cathode-ray tubes
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
(CRTs), which were all that could be produced given the manufacturing
Manufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...
technology
Technology
Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...
of the time. (Today's CRT technology allows the manufacture of much wider tubes, and the flat-screen technologies which are becoming steadily more popular have no technical aspect ratio limitations at all.) The BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
's television service used a more squarish 5:4 ratio from 1936 to 3 April 1950, when it too switched to a 4:3 ratio. This did not present significant problems, as most sets at the time used round tubes which were easily adjusted to the 4:3 ratio when the transmissions changed.
Movie studio
A movie studio is a term used to describe a major entertainment company or production company that has its own privately owned studio facility or facilities that are used to film movies...
s moved towards widescreen
Widescreen
Widescreen images are a variety of aspect ratios used in film, television and computer screens. In film, a widescreen film is any film image with a width-to-height aspect ratio greater than the standard 1.37:1 Academy aspect ratio provided by 35mm film....
aspect ratios such as CinemaScope
CinemaScope
CinemaScope was an anamorphic lens series used for shooting wide screen movies from 1953 to 1967. Its creation in 1953, by the president of 20th Century-Fox, marked the beginning of the modern anamorphic format in both principal photography and movie projection.The anamorphic lenses theoretically...
in an effort to distance their product from television. Although this was initially just a gimmick
Gimmick
In marketing language, a gimmick is a unique or quirky special feature that makes something "stand out" from its contemporaries. However, the special feature is typically thought to be of little relevance or use. Thus, a gimmick is a special feature for the sake of having a special feature...
, widescreen is still the format of choice today and 4:3 aspect ratio movies are rare.
Yet the various television systems were not originally designed to be compatible with film at all. Traditional, narrow-screen movies are projected onto a television camera either so that the top of the screens line up to show facial features, or, for films with subtitles, the bottoms. What this means is that filmed newspapers or long captions filling the screen for explanation are cut off at each end. Similarly, while the frame rate of sound films is 24 per second, the screen scanning rate of the NTSC is 29.97 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
(per second), which requires a complex scanning schedule. That of PAL and SECAM are 50 Hz, which means that films are shortened (and the sound is offkey) by scanning each frame twice for 25 per second.
The switch to digital television
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
systems has been used as an opportunity to change the standard television picture format from the old ratio of 4:3 (1.33:1) to an aspect ratio of 16:9 (approximately 1.78:1). This enables TV to get closer to the aspect ratio of modern widescreen movies
Film
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...
, which range from 1.66:1 through 1.85:1 to 2.35:1. There are two methods for transporting widescreen content, the most common of which uses what is called anamorphic widescreen format. This format is very similar to the technique used to fit a widescreen movie frame inside a 1.33:1 35 mm film frame. The image is compressed horizontally when recorded, then expanded again when played back. The anamorphic widescreen 16:9 format was first introduced via European PALplus
PALplus
PALplus is an extension of the PAL analogue broadcasting system for transmitting 16:9 programs without sacrificing vertical resolution. It followed experiences with the HD-MAC and D2-MAC, standards that were incompatible with existing receivers but featured a 16:9 aspect ratio...
television broadcasts and then later on "widescreen" Laser Discs and DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
s; the ATSC HDTV
High-definition television
High-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...
system uses straight widescreen format, no horizontal compression or expansion is used.
Recently "widescreen" has spread from television to computing where both desktop
Desktop computer
A desktop computer is a personal computer in a form intended for regular use at a single location, as opposed to a mobile laptop or portable computer. Early desktop computers are designed to lay flat on the desk, while modern towers stand upright...
and laptop
Laptop
A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...
computers are commonly equipped with widescreen displays. There are some complaints about distortions of movie picture ratio due to some DVD playback software not taking account of aspect ratios; but this may subside as the DVD playback software matures. Furthermore, computer and laptop widescreen displays are in the 16:10 aspect ratio both physically in size and in pixel counts, and not in 16:9 of consumer televisions, leading to further complexity. This was a result of widescreen computer display engineers' assumption that people viewing 16:9 content on their computer would prefer that an area of the screen be reserved for playback controls, subtitles or their Taskbar, as opposed to viewing content full-screen.
Aspect ratio incompatibility
The television industry's changing of aspect ratiosAspect ratio (image)
The aspect ratio of an image is the ratio of the width of the image to its height, expressed as two numbers separated by a colon. That is, for an x:y aspect ratio, no matter how big or small the image is, if the width is divided into x units of equal length and the height is measured using this...
is not without difficulties, and can present a considerable problem.
Displaying a widescreen aspect (rectangular) image on a conventional aspect (square or 4:3) display can be shown:
- in "letterboxLetterboxLetterboxing is the practice of transferring film shot in a widescreen aspect ratio to standard-width video formats while preserving the film's original aspect ratio. The resulting videographic image has mattes above and below it; these mattes are part of the image...
" format, with black horizontal bars at the top and bottom - with part of the image being cropped, usually the extreme left and right of the image being cut off (or in "pan and scanPan and scanPan and scan is a method of adjusting widescreen film images so that they can be shown within the proportions of a standard definition 4:3 aspect ratio television screen, often cropping off the sides of the original widescreen image to focus on the composition's most important aspects...
", parts selected by an operator or a viewer) - with the image horizontally compressed
A conventional aspect (square or 4:3) image on a widescreen aspect (rectangular with longer horizon) display can be shown:
- in "pillar boxPillar box (film)The pillarbox effect occurs in widescreen video displays when black bars are placed on the sides of the image. It becomes necessary when film or video that was not originally designed for widescreen is shown on a widescreen display, or a narrower widescreen image is displayed within a wider...
" format, with black vertical bars to the left and right - with upper and lower portions of the image cut off (or in "tilt and scan", parts selected by an operator)
- with the image vertically compressed
A common compromise is to shoot or create material at an aspect ratio of 14:9, and to lose some image at each side for 4:3 presentation, and some image at top and bottom for 16:9 presentation. In recent years, the cinematographic process known as Super 35 (championed by James Cameron
James Cameron
James Francis Cameron is a Canadian-American film director, film producer, screenwriter, editor, environmentalist and inventor...
) has been used to film a number of major movies such as Titanic
Titanic (1997 film)
Titanic is a 1997 American epic romance and disaster film directed, written, co-produced, and co-edited by James Cameron. A fictionalized account of the sinking of the RMS Titanic, it stars Leonardo DiCaprio as Jack Dawson, Kate Winslet as Rose DeWitt Bukater and Billy Zane as Rose's fiancé, Cal...
, Legally Blonde
Legally Blonde
Legally Blonde is a 2001 American comedy film directed by Robert Luketic, written by Karen McCullah Lutz and Kirsten Smith, and produced by Marc E. Platt...
, Austin Powers
Austin Powers (film series)
The Austin Powers series is a series of action-comedy films written by and starring Mike Myers as the title character, directed by Jay Roach and distributed by New Line Cinema...
, and Crouching Tiger, Hidden Dragon
Crouching Tiger, Hidden Dragon
Crouching Tiger, Hidden Dragon is a 2000 wuxia film. An American-Chinese-Hong Kong-Taiwanese co-production, the film was directed by Ang Lee and featured an international cast of ethnic Chinese actors, including Chow Yun-Fat, Michelle Yeoh, Zhang Ziyi, and Chang Chen...
(see also: Films shot in Super 35). This process results in a camera-negative which can then be used to create both wide-screen theatrical prints, and standard "full screen" releases for television/VHS/DVD which avoid the need for either "letterbox
Letterbox
Letterboxing is the practice of transferring film shot in a widescreen aspect ratio to standard-width video formats while preserving the film's original aspect ratio. The resulting videographic image has mattes above and below it; these mattes are part of the image...
ing" or the severe loss of information caused by conventional "pan-and-scan" cropping.
NTSC
In North America, the basic signal standards since 1941 had been compatible enough in 2007 that even the oldest monochrome televisions could still receive color broadcasts. However, the United States Congress passed a law which required the cessation of all conventional television broadcast signals by February 2009. After that date all NTSCNTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
standard televisions with analog-only tuners went dark unless fitted with a digital ATSC tuner
ATSC tuner
An ATSC tuner, often called an ATSC receiver or HDTV tuner is a type of television tuner that allows reception of digital television television channels transmitted by television stations in North America, parts of Central America and South Korea that use ATSC standards...
, and the spectrum previously occupied by those analog channels was auctioned off by the United States' Federal Communications Commission for other uses.
PAL and SECAM
PALPAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
and SECAM
SECAM
SECAM, also written SÉCAM , is an analog color television system first used in France....
are expected not to be broadcast in Europe and Eurasia by the mid-2020s. PAL-M may have a similar decommissioning timeline.
The European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
has recommended its members to close down analogue terrestrial television by 2012. Luxembourg and the Netherlands already completed their closedowns in 2006, and Finland and Sweden closed down their analogue broadcasts in 2007.
Britain started its digital switch in October 2007. At 2AM on Wednesday 17 October 2007, the BBC2 transmitter covering the Whitehaven and Copeland areas (NW England) was disabled. The remaining four analogue channels ceased broadcasting shortly after. The original five channels are now available only in digital form, alongside approximately 15 additional free-to-air channels.
New developments
- 3D television3D televisionA 3D television is a television set that employs techniques of 3D presentation, such as stereoscopic capture, multi-view capture, or 2D-plus-depth, and a 3D display – a special viewing device to project a television program into a realistic three-dimensional field.- History :In the late-1890's,...
- AmbilightAmbilightAmbilight, which is short for Ambient Lighting Technology, is a feature invented by Philips Electronics, generating light effects around the TV that correspond to the video content. The effect, the company claims, is a larger virtual screen and a more immersive viewing experience. In addition,...
- Broadcast flagBroadcast flagA broadcast flag is a set of status bits sent in the data stream of a digital television program that indicates whether or not the data stream can be recorded, or if there are any restrictions on recorded content...
- CableCARDCableCARDCableCARD is a special-use PCMCIA card that allows consumers in the United States to view and record digital cable television channels on digital video recorders, personal computers and television sets without the use of other equipment such as a set top box provided by a cable television company...
- Digital Light Processing (DLP)
- Digital Rights ManagementDigital rights managementDigital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...
(DRM) - Digital televisionDigital televisionDigital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
(DTV) - Digital Video RecorderDigital video recorderA digital video recorder , sometimes referred to by the merchandising term personal video recorder , is a consumer electronics device or application software that records video in a digital format to a disk drive, USB flash drive, SD memory card or other local or networked mass storage device...
s (DVR) - Direct Broadcast SatelliteDirect broadcast satelliteDirect broadcast satellite is a term used to refer to satellite television broadcasts intended for home reception.A designation broader than DBS would be direct-to-home signals, or DTH. This has initially distinguished the transmissions directly intended for home viewers from cable television...
TV (DBS) - DVDDVDA DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
and HD DVDHD DVDHD DVD is a discontinued high-density optical disc format for storing data and high-definition video.Supported principally by Toshiba, HD DVD was envisioned to be the successor to the standard DVD format...
standards - Blu-ray DiscBlu-ray DiscBlu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...
- Flat panel displayFlat panel displayFlat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
- Flicker-freeFlicker-freeFlicker-free is a term given to televisions that operate at a 100 or 120 hertz field rate to eliminate flicker, compared to standard televisions that operate at 50 Hz or 60 Hz...
(100 Hz or 120 Hz, depending on country) - High Definition TV (HDTV)
- High-Definition Multimedia InterfaceHigh-Definition Multimedia InterfaceHDMI is a compact audio/video interface for transmitting uncompressed digital data. It is a digital alternative to consumer analog standards, such as radio frequency coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, or VGA...
(HDMI) - IPTVIPTVInternet Protocol television is a system through which television services are delivered using the Internet protocol suite over a packet-switched network such as the Internet, instead of being delivered through traditional terrestrial, satellite signal, and cable television formats.IPTV services...
also known as Internet televisionInternet televisionInternet television is the digital distribution of television content via the Internet...
(IPTV) - Laser TVLaser TVLaser color television , or Laser color video display utilizes two or more individually modulated optical rays of different colors to produce a combined spot that is scanned and projected across the image plane by a polygon-mirror system or less effectively by optoelectronic means to produce a...
display technology
- Liquid crystal display televisionLiquid crystal display televisionLiquid-crystal display televisions are television sets that use LCD display technology to produce images. LCD televisions are thinner and lighter than cathode ray tube of similar display size, and are available in much larger sizes...
(LCD) - Mirror TVMirror TVA "Mirror TV" or "TV Mirror" is any device that is convertible from a television to a mirror. Mirror TVs are often utilized to save space or discreetly conceal unsightly electronics in living areas such as bedrooms and living rooms...
- OLED TV - Roll up TV (using organic light-emitting diodes)
- P2PTVP2PTVThe term P2PTV refers to peer-to-peer software applications designed to redistribute video streams in real time on a P2P network; the distributed video streams are typically TV channels from all over the world but may also come from other sources...
- Pay-per-viewPay-per-viewPay-per-view provides a service by which a television audience can purchase events to view via private telecast. The broadcaster shows the event at the same time to everyone ordering it...
- Personal video recorders (PVR)
- Picture-in-picturePicture-in-picturePicture in Picture is a feature of some television receivers and similar devices. One program is displayed on the full TV screen at the same time as one or more other programs are displayed in inset windows. Sound is usually from the main program only.Picture in Picture requires two independent...
(PiP) - PixelplusPixelplusPixel Plus, is a proprietary digital filter image processing technology developed by Philips, who claims that it enhances the display of analogue broadcast signals on their TVs....
- Placeshifting
- Plasma displayPlasma displayA plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
- Remote controlRemote controlA remote control is a component of an electronics device, most commonly a television set, used for operating the television device wirelessly from a short line-of-sight distance.The remote control is usually contracted to remote...
s - Surface-conduction electron-emitter displaySurface-conduction Electron-emitter DisplayA surface-conduction electron-emitter display is a display technology which is currently developing various flat panel displays by a number of companies as a electronic visual displays. SEDs use nanoscopic-scale electron emitters to energize colored phosphors and produce an image...
(SED) display technology - The SlingboxSlingboxThe Slingbox is a TV streaming media device made by Sling Media that encodes video into the VC-1 format for transmission over the Internet and provides an infrared blaster. The video encoding and IR blaster can both be operated remotely over the Internet...
- Time shiftingTime shiftingTime shifting is the recording of programming to a storage medium to be viewed or listened to at a time more convenient to the consumer. Typically, this refers to TV programming but can also refer to radio shows via podcasts....
- Video on-demand (VOD)
- Ultra High Definition Television (UHDTV)
- Web TVWeb TVWeb TV may refer to:* MSN TV , a thin client which uses a television for display and the online service that supports it* Web television, an emerging genre of digital entertainment...
Exterior designs
In the early days of television, cabinets were made of wood grain (often simulated particularly in the later years), however, they went out of style in the 1980s. Up until the late 1970s, console TV/Hi Fi's were common. These were large (about 6' wide by 4' high) wooden cabinets containing a television, speakers, radioRadio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
and a turntable
Turntable
A turntable is generally a rotating platform, and may refer to:-Music:* Turntable, a motor-driven platform that normally rotates a gramophone record at a constant rotational velocity as part of a phonograph....
.
See also
- Broadcast safe
- Electronic wasteElectronic wasteElectronic waste, e-waste, e-scrap, or Waste Electrical and Electronic Equipment describes discarded electrical or electronic devices. There is a lack of consensus as to whether the term should apply to resale, reuse, and refurbishing industries, or only to product that cannot be used for its...
- History of display technology
- History of televisionHistory of televisionThe history of television records the work of numerous engineers and inventors in several countries over many decades. The fundamental principles of television were initially explored using electromechanical methods to scan, transmit and reproduce an image...