Television is a telecommunication system for broadcasting and receiving moving pictures and sound over a distance. The term has come to refer to all the aspects of television from the television set to the programming and transmission. The word is derived from mixed Latin and Greek roots, meaning "far sight": Greek Ïá¿Î»Îµ "tele", far, and Latin visio-n, sight (from video, vis- to see).
Contents [hide]
1 History
2 Technology
2.1 Elements of a television system
2.2 Display technology
2.3 Terminology for televisions
2.4 Transmission band
2.5 Aspect ratios
2.5.1 Aspect ratio incompatibility
2.6 Sound
2.7 Television add-ons
2.8 New developments
3 Geographical usage
4 Content
4.1 Advertising
4.2 Programming
5 Social aspects
5.1 Alleged dangers
5.2 Technology trends
5.3 Suitability for audience
6 See also
7 Further reading
8 References
9 External links
[edit]
History
Main article: History of television
The origins of what would become today's television system can be traced back as far as the discovery of the photoconductivity of the element selenium by Willoughby Smith in 1873 and the invention of a scanning disk by Paul Nipkow in 1884. All practical television systems use the fundamental idea of scanning an image to produce a time series signal representation. That representation is then transmitted to a device to reverse the scanning process. The final device, the television (or T.V. set), relies on the human eye to integrate the result into a coherent image.
Electromechanical techniques were developed prior to World War II, most notably by Charles Francis Jenkins and John Logie Baird. Baird gave the world's first public demonstration of a working television system that transmitted moving images with tone graduation (grayscale) on 26 January 1926 at his laboratory in London. Baird further demonstrated the world's first color television transmission on 3 July 1928.
Completely electronic television systems relied on the inventions of Philo Taylor Farnsworth, Vladimir Zworykin and others to produce a system suitable for mass distribution of television programming. Farnsworth gave the world's first public demonstration of an all-electronic television system at the Franklin Institute in Philadelphia on 25 August 1934.
Regular broadcast programming occurred in the United States,[1] the United Kingdom,[2] Germany,[3] France,[4] and the Soviet Union[5] before World War II. The first regular television broadcasts with a modern level of definition (240 or more lines) were made in England in 1936, soon upgraded to the so-called "System A" with 405 lines. Large scale network broadcasting began in the United States in 1946, and television became common in American homes by the middle 1950s. While North American over-the-air broadcasting was originally free of direct marginal cost to the consumer (i.e., cost in excess of acquisition and upkeep of the hardware) and broadcasters were compensated primarily by receipt of advertising revenue, increasingly United States television consumers obtain their programming by subscription to cable television systems or direct-to-home satellite transmissions. In the United Kingdom, on the other hand, the owner of each television must pay a licence fee annually which is used to support the British Broadcasting Corporation.
[edit]
Technology
[edit]
Elements of a television system
The elements of a simple television system are:
An image source - this may be a camera for live pick-up of images or a flying spot scanner for transmission of films
A sound source.
A transmitter, which modulates one or more television signals with both picture and sound information for transmission.
A receiver (television) which recovers the picture and sound signals from the television broadcast.
A display device, which turns the electrical signals into visible light.
A sound device , which turns electrical signals into sound waves to go along with the picture.
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. Transmission may be over the air from land-based transmitters, over metal or optical cables, or by radio from synchronous satellites. 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.
[edit]
Display technology
Thanks to advances in display technology, there are now several kinds of video displays used in modern TV sets:
CRT: The most common displays are direct-view CRTs for up to 40 in (100 cm) (in 4:3) and 46 in (115 cm) (in 16:9) diagonally. These are still the least expensive, and are a refined technology that can still provide the best overall picture quality. As they do not have a fixed native resolution, in some cases they are also capable of displaying sources with a variety of different resolutions at the best possible image quality. The frame rate or refresh rate of a typical NTSC format CRT TV is 60 Hz, and for the PAL format, it is 50 Hz. A typical NTSC 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 Interval, or VBI, allows other signals to be carried along with the broadcast.
Rear projection: Most very large screen TVs (up to over 100 inch (254 cm)) use projection technology. Three types of projection systems are used in projection TVs: CRT-based, LCD-based, and DLP (reflective micromirror chip) -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 projector, using similar technology, which projects onto a screen.
Flat panel LCD or plasma: Modern advances have brought flat panels to TV that use active matrix LCD or plasma display technology. Flat panel LCDs and plasma displays are as little as 1 inch thick and can be hung on a wall like a picture or put over a pedestal. Some models can also be used as computer monitors.
See also: Liquid crystal display television
Each has its pros and cons. Flat panel LCD display can have narrow viewing angles and so may not suit a home environment. Rear projection screens do not perform well in natural daylight or well lit rooms and so are best suited to dark viewing areas. A complete run down of the pros and cons of each display should be sought before purchasing a single television technology.
[edit]
Terminology for televisions
Pixel resolution is the amount of individual points known as pixels on a given screen. A typical resolution of 800x600 means that the television display has 800 pixels across and 600 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 brightest 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 colours are. Measured in cd / m2 equivalent to the amount of candles required to power the image.
[edit]
Transmission band
There are various bands of frequencies on which televisions work 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 BBC initially used Band I VHF at 45 MHz, this frequency is 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 satellite broadcasting, which uses frequencies around 10 GHz. TV systems in most countries relay the video as an AM (amplitude-modulation) signal and the sound as a FM (frequency-modulation) signal. An exception is France, where the sound is AM.
[edit]
Aspect ratios
Aspect ratio 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 1950s, movie studios 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 square aspect ratio movies are rare. Some people argue that widescreen is actually a disadvantage when showing objects that are tall instead of panoramic, others say that natural vision is more panoramic than tall, and therefore widescreen is easier on the eye.
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 better 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 35mm 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" DVDs; 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' uninformed 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.
[edit]
Aspect ratio incompatibility
The television industry's changing of aspect ratios 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 "letterbox" 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 scan", parts selected by an operator)
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 box" 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 horizontally distorted
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: List of top-grossing 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 "letterboxing" or the severe loss of information caused by conventional "pan-and-scan" cropping.
[edit]
Sound
Further information: NICAM
[edit]
Television add-ons
Today there are many television add-ons including Video Game Consoles, VCRs, Set-top boxes for Cable, Satellite and DVB-T compliant Digital Television reception, DVD players, or Digital Video Recorders (including personal video recorders, PVRs). The add-on market continues to grow as new technologies are developed.
[edit]
New developments
Ambilightâ¢
Blu ray
Broadcast flag
CableCARDâ¢
Digital Light Processing (DLP)
Digital Rights Management (DRM)
Digital television (DTV)
Digital Video Recorders
Direct Broadcast Satellite TV (DBS)
DVD
Flicker-free (100 Hz or 120 Hz, depending on country)
HD DVD
High Definition TV (HDTV)
High-Definition Multimedia Interface (HDMI)
IPTV
Internet television
LCD and Plasma display Flat screen TV
SED display technology
OLED display technology
P2PTV
Pay-per-view
Picture-in-picture (PiP)
Pixelplus
Remote controls
Video on-demand (VOD)
Ultra High Definition Video (UHDV)
Web TV
[edit]
Geographical usage
Timeline of the introduction of television in countries
Main article: Geographical usage of television
[edit]
Content
[edit]
Advertising
Since their inception in the USA in 1940, TV commercials have become one of the most effective, most pervasive, and most popular methods of selling products of many sorts, especially consumer goods. U.S. advertising rates are determined primarily by Nielsen Ratings.
[edit]
Programming
Getting TV programming shown to the public can happen in many different ways. After production the next step is to market and deliver the product to whatever markets are open to using it. This typically happens on two levels:
Original Run or First Run - a producer creates a program of one or multiple episodes and shows it on a station or network which has either paid for the production itself or to which a license has been granted by the producers to do the same.
Syndication - this is the terminology rather broadly used to describe secondary programming usages (beyond original run). It includes secondary runs in the country of first issue, but also international usage which may or may not be managed by the originating producer. In many cases other companies, TV stations or individuals are engaged to do the syndication work, in other words to sell the product into the markets they are allowed to sell into by contract from the copyright holders, in most cases the producers.
In most countries, the first wave occurs primarily on free-to-air (FTA) television, while the second wave happens on subscription TV and in other countries. In the U.S., however, the first wave occurs on the FTA networks and subscription services, and the second wave travels via all means of distribution.
First run programming is increasing on subscription services outside the U.S., but few domestically produced programs are syndicated on domestic FTA elsewhere. This practice is increasing however, generally on digital-only FTA channels, or with subscriber-only first run material appearing on FTA.
Unlike the U.S., repeat FTA screenings of a FTA network program almost only occur on that network. Also, Affiliates rarely buy or produce non-network programming that isn't centred around local events.
[edit]
Social aspects
[edit]
Alleged dangers
Paralleling television's growing primacy in family life and society, an increasingly vocal chorus of legislators, scientists and parents are raising objections to the uncritical acceptance of the medium. For example, the Swedish government imposed a total ban on advertising to children under twelve in 1991 (see advertising). Fifty years of research on the impact of television on children's emotional and social development (Norma Pecora, John P. Murray, & Ellen A. Wartella, Children and Television: 50 Years of Research, published by Erlbaum Press, June, 2006) demonstrate that there are clear and lasting effects of viewing violence. In a recent study (February, 2006) published in the journal Media Psychology, volume 8, number 1, pages 25-37, the research team demonstrated that the brain activation patterns of children viewing violence show that children are aroused by the violence (increased heart rates), demonstrate fear (activation of the amygdala-the fight or flight sensor in the brain) in response to the video violence, and store the observed violence in an area of the brain (the posterior cingulate) that is reserved for long-term memory of traumatic events.
A 23 February 2002 article in Scientific American suggested that compulsive television watching was no different from any other addiction, a finding backed up by reports of withdrawal symptoms among families forced by circumstance to cease watching.
A longitudinal study in New Zealand involving 1000 people (from childhood to 26 years of age) demonstrated that "television viewing in childhood and adolescence is associated with poor educational achievement by 26 years of age". In other words, the more the child watched television, the less likely he or she was to finish school and enroll in a university.
In Iceland, television broadcasting hours were restricted until 1984, with no television programs being broadcast on Thursday, or during the whole of July.
Despite this research, many media scholars today dismiss such studies as flawed. For one example of this school of thought, see David Gauntlett's article "Ten Things Wrong With the Media 'Effects' Model."
[edit]
Technology trends
In its infancy, television was an ephemeral medium. Fans of regular shows planned their schedules so that they could be available to watch their shows at their time of broadcast. The term appointment television was coined by marketers to describe this kind of attachment.
The viewership's dependence on schedule lessened with the invention of programmable video recorders, such as the Videocassette recorder and the Digital video recorder. Consumers could watch programs on their own schedule once they were broadcast and recorded. Television service providers also offer video on demand, a set of programs which could be watched at any time.
Both mobile phone networks and the Internet are capable of carrying video streams. There is already a fair amount of Internet TV available, either live or as downloadable programs. Mobile phone TV is planned to eventually become mainstream, after worldwide over-the-air digital TV takes over analogue and some technical difficulties can be overcome - especially the ones related to battery life.
[edit]
Suitability for audience
Almost since the medium's inception there have been charges that some programming is, in one way or another, inappropriate, offensive or indecent. Critics such as Jean Kilborne have claimed that television, as well as other mass media images, harm the self image of young girls. Other commentators such as Sut Jhally, make the case that television advertising in the U.S. has been so effective that happiness has increasingly come to be equated with the purchasing of products. George Gerbner has presented evidence that the frequent portrayals of crime, especially minority crime, has led to the Mean World Syndrome, the view among frequent viewers of television that crime rates are much higher than the actual data would indicate. In addition, a lot of television has been charged with presenting propaganda, political or otherwise, and been pitched at a low intellectual level.
[edit]
See also
Andy Kaufman and Judd Hirsch on the cover of TV Guide, June 6th, 1981Golden Age of Television
Archive of American Television
BARB
Composite monitor
European Broadcasting Union (EBU)
Electronic field production
Electronic news gathering
History of television
List of television topics
List of 'years in television'
Lists of television channels
List of television programs/series
List of television personalities
Live television
Museum of Broadcast Communications
PC card
PVR (Personal Video Recorder).
S-video monitor
Teletext
TV/VCR combo
Long distance television reception (TV DX)
TV listings
TV Guide
[edit]
Further reading
Erik Barnouw, Tube of Plenty: The Evolution of American Television, Oxford University Press, 1992.
Pierre Bourdieu, On Television, The New Press, 2001.
Brooks, Tim and March, Earle, The Complete Guide to Prime Time Network and Cable TV Shows, Ballantine, Eighth Edition, 2002.
Guy Debord, The Society of the Spectacle, Zone Books, 1995.
Jacques Derrida, Bernard Stiegler, Echographies of Television, Polity Press, 2002.
Jerry Mander, Four Arguments for the Elimination of Television, Perennial, 1978.
Neil Postman, Amusing Ourselves to Death: Public Discourse in the Age of Show Business. Penguin USA, 1985. ISBN 0-670-80454-1
Dr. Aric Sigman, Remotely Controlled: How Television Is Damaging Our Lives — And What We Can Do About It, Vermilion, 2005.
Beretta E. Smith-Shomade, Shaded Lives: African-American Women and Television, Rutgers University Press, 2002.
[edit]
References
^ See RGB History, How Television Came to Boston: The Forgotten Story of W1XAY, and W3XK — America's first television station.
^ See J.L. Baird: Television in 1934.
^ See Museum of Broadcast Communications: Germany and Berlin 1936: Television in Germany.
^ See The Eiffel Tower Television Installation.
^ See R. W. Burns, Television: An International History of the Formative Years. IET, 1998, p. 488. ISBN 0852969147, and RCA's Russian Television Connection.
David E. Fisher and Marshall J. Fisher, Tube: the Invention of Television, Counterpoint, Washington D.C. USA, (1996) ISBN 1-887178-17-1
Albert Abramson, The History of Television, 1942 to 2000, McFarland, Jefferson, NC, USA, and London (2003) ISBN 0-7864-1220-8
[edit]
External links
Find more information on Television by searching Wikipedia's sister projects:
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Source texts from Wikisource
Images and media from Commons
News stories from Wikinews
BBC Television
A directory of world television channels
Television History — The First 75 Years
TV Type Guide
The Encyclopedia of Television at the Museum of Broadcast Communications
MZTV Museum of Television Some of the rarest sets in America
The #1 Online Television Resource
Cherished Television
CNET News.com's Me TV Wiki, about the future of television.
Retrieved from "http://en.wikipedia.org/wiki/Television"
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High-definition television (HDTV) is a television broadcasting system with a significantly higher resolution than traditional formats (NTSC, SECAM, PAL) allow. Except for early analog formats in Europe and Japan, HDTV is broadcast digitally, and therefore its introduction sometimes coincides with the introduction of digital television (DTV): this technology was first introduced in the USA during the 1990s, by the Digital HDTV Grand Alliance (grouping together AT&T, General Instrument, MIT, Philips, Sarnoff, Thomson, and Zenith)[1].
While a number of high-definition television standards have been proposed or implemented on a limited basis, the current HDTV standards are defined in ITU-R BT.709 as 1080 active interlaced or progressive lines, or 720 progressive lines, using a 16:9 aspect ratio. The term "high-definition" can refer to the resolution specifications themselves, or more loosely to media capable of similar sharpness, such as photographic film.
Contents [hide]
1 Notation
1.1 Changes in notation
1.2 Standard resolutions
1.3 Standard frame or field rates
2 Comparison to SDTV
2.1 Close-up view
3 Format considerations
4 Technical details
5 Advantages of HDTV expressed in non-engineering terms
6 Early systems
7 Contemporary systems
8 Recording and compression
9 Table of terrestrial HDTV transmission systems
10 References
11 See also
12 External links
[edit]
Notation
In the context of HDTV, the formats of the broadcasts are referred to using a notation describing:
The number of lines in the vertical display resolution.
Whether progressive frames (p) or interlaced fields (i) are used.
The number of frames or fields per second.
For example, the format 720p60 is 1280 Ã 720 pixels, progressive encoding with 60 frames per second (60 hertz known as Hz). The format 1080i50 is 1920 Ã 1080 pixels, interlaced encoding with 50 fields (25 frames) per second. Often the frame or field rate is left out, indicating only the resolution and type of the frames or fields. Sometimes the rate is then to be inferred from the context, in which case it can usually be assumed to be either 50 or 60, except for 1080p which is often used to denote either 1080p24, 1080p25 or 1080p30 at present but will also denote 1080p50 and 1080p60 in the future.
A frame or field rate can also be specified without a resolution. For example 24p means 24 progressive frames per second and 50i means 25 interlaced frames per second, consisting of 50 interlaced fields per second.
Most HDTV systems support some standard resolutions and frame or field rates. The most common are noted below.
[edit]
Changes in notation
It should be noted that the terminology described above was invented for digital systems in the 1990s. Before that, analog TV had no true "pixels" to measure horizontal resolution, and vertical scan-line count included off-screen scan lines with no picture information while the CRT beam returned to the top of the screen to begin another field. Thus NTSC was considered to have "525 lines" even though only 480 of them had a picture (625/576 for PAL). Similarly the Japanese MUSE system was called "1125 line", but is only 1035i by today's measuring standards. This change was made because digital systems have no need of blank retrace lines unless the signal was converted to analog to drive a CRT.
[edit]
Standard resolutions
We distinguish (a) the resolution of the transmitted signal and (b) the (native) displayed resolution of a TV set. Digital NTSC- and PAL/SECAM-like signals (480i60 and 576i50 respectively) are transmitted at a horizontal resolutions of 720 or 704 "pixels". However these transmitted DTV "pixels" are not square, and have to be stretched for correct viewing. PAL TV sets with an aspect ratio of 4:3 use a fixed pixel grid of 768 Ã 576 or 720 x 540; with an aspect ratio of 16:9 they use 1024 Ã 576 or 960 Ã 540; NTSC ones use 640 Ã 480 and 852 Ã 480 or, seldomly, 720 Ã 540.
[edit]
Standard frame or field rates
23.976p (allow easy conversion to NTSC)
24p (cinematic film, including 18fps/20fps silent film speed)
25p (PAL, SECAM DTV progressive material)
30p (NTSC DTV progressive material)
50p (PAL, SECAM DTV progressive material)
60p (NTSC DTV progressive material)
50i (PAL, PAL-M & SECAM)
60i (NTSC)
[edit]
Comparison to SDTV
HDTV has at least twice the lineal resolution of standard-definition television (SDTV), thus allowing much more detail to be shown compared to analog television or regular DVD. In addition, the technical standards for broadcasting HDTV are also able to handle 16:9 aspect ratio pictures without using letterboxing, thus further increasing the effective resolution for such content.
[edit]
Close-up view
HDTV at four times the spatial resolution of SDTV.
SDTV resolution.
[edit]
Format considerations
The optimum formats for a broadcast depends on the type of media used for the recording and the characteristics of the content. The field and frame rate should match the source, as should the resolution. On the other hand, a very high resolution source may require more bandwidth than is available in order to be transmitted without loss of fidelity. The lossy compression that is used in all digital HDTV storage/transmission systems will then cause the received picture to appear distorted when compared to the uncompressed source.
Photographic film destined for the theater typically has a high resolution and is photographed at 24 frame/s. Depending on the available bandwidth and the amount of detail and movement in the picture, the optimum format for video transfer is thus either 720p24 or 1080p24. When shown on television in countries using PAL, film must be converted to 25 frames per second by speeding it up by 4.1%. In countries using the NTSC standard, (60 fps) a technique called 3:2 pulldown is used. One film frame is held for three video fields, (1/20 of a second) and then the next is held for two video fields (1/30 of a second) and then the process repeats, thus achieving the correct film rate with two film frames shown in 1/12 of a second. (See also: Telecine)
Older (pre-HDTV) recordings on video tape such as Betacam SP are often either in the form 480i60 or 576i50. These may be upconverted to a higher resolution format (720i), but removing the interlace to match the common 720p format may distort the picture or require filtering which actually reduces the resolution of the final output. (See also: Deinterlacing)
Non-cinematic HDTV video recordings are recorded in either 720p or 1080i format. The format depends on the broadcast company if destined for television broadcast; however, in other scenarios the format choice will vary depending on a variety of factors. In general, 720p is more appropriate for fast action as it uses progressive fields, as opposed to 1080i which uses interlaced fields and thus can have a degradation of image quality with fast motion. In addition, 720p is used more often with Internet distribution of HD video, as all computer monitors are progressive, and most graphics cards do a poor job of de-interlacing video in real time. 720p Video also has lower storage and decoding requirements than 1080i or 1080p, and few people possess displays capable of displaying the 1920x1080 resolution without scaling. 720p appears at full resolution on a common 1280x1024 LCD, which can be found for under $250. An LCD capable of native 1080p resolution costs close to 300 dollars.
In North America, Fox, ABC, and ESPN (ABC and ESPN are both owned by Disney) currently broadcast 720p content. NBC, Universal HD (both owned by General Electric), CBS, HBO-HD, INHD, HDNet ,TNT, and Discovery HD Theater currently broadcast 1080i content.
[edit]
Technical details
One of the first DVB-S2 tuner cards.MPEG-2 is most commonly used as the compression codec for digital HDTV broadcasts. Although MPEG-2 supports up to 4:2:2 YCbCr chroma subsampling and 10-bit quantization, HD broadcasts use 4:2:0 and 8-bit quantization to save bandwidth. Some broadcasters also plan to use MPEG-4 AVC, such as the BBC which is trialling such a system via satellite broadcast, which save considerable bandwidth compared to MPEG-2 systems. Some German broadcasters already use MPEG-4 together with DVB-S2 (ProSieben, Sat1 and Three Premiere Channels). Although MPEG-2 is more widely used at present, it seems likely that in the future all European HDTV may be MPEG-4, and Ireland and Norway, which have not yet begun any digital television broadcasts, are considering MPEG4 for SD Digital as well as HDTV on terrestrial broadcasts.
HDTV is capable of "theater-quality" audio because it uses the Dolby Digital (AC-3) format to support "5.1" surround sound.
The pixel aspect ratio of native HD signals is a "square" 1.0, or 1 pixel length = 1 pixel width. New HD compression and recording formats such as HDV use rectangular pixels for more efficient compression and to open HDTV acquisition for the consumer market.
For more technical details see the articles on HDV, ATSC, DVB, and ISDB.
Within television studios and other production and distribution facilities, HD-SDI SMPTE 292M interconnect standard (a nominally 1.485 Gbit/s, 75-ohm serial digital interface) is used to route uncompressed HDTV signals. The native bitrate of HDTV formats cannot be supported by 6-8MHz standard-definition television channels for over-the-air broadcast and consumer distribution media, hence the widespread use of compression in consumer applications. SMPTE 292M interconnects are generally unavailable in consumer equipment, partially due to the expense involved in supporting this format, and partially because consumer electronics manufacturers are required (typically by licensing agreements) to provide encrypted digital outputs on consumer video equipment, for fear that this would aggravate the issue of video piracy.
Newer dual-link HD-SDI signals are needed for the latest 4:4:4 camera systems (Sony HDC-F950 & Thomson Viper), where one link/coax cable contains the 4:2:2 YCbCr info and the other link/coax cable contains the additional 0:2:2 CbCr information.
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Advantages of HDTV expressed in non-engineering terms
All commercial HD is digital, so the signal will either deliver an excellent picture, a picture with noticeable pixelation, a series of still pictures, or no picture at all. The system cannot produce a snowy or washed out image from a weak signal, effects from signal interference, such as herringbone patterns, or vertical rolling.
HD programming and films will be presented in 16:9 widescreen format (although films created in even wider ratios will still display "letterbox" bars on the top and bottom of even 16:9 sets.) Older films and programming that retain their 4:3 ratio display will be presented in a version of letterbox commonly called "pillar box", displaying bars on the right and left of 16:9 sets (rendering the term "fullscreen" a misnomer). Or, one can usually choose to zoom the image to fill the screen.
The colors will generally look more realistic, due to their greater bandwidth.
The visual information is about 2-5 times more detailed overall. The gaps between scanning lines are smaller or invisible. Legacy TV content that was shot and preserved on 35 mm film can now be viewed at nearly the same resolution as that at which it was originally photographed.
Two new pre-recorded disc formats support HDTV resolutions, namely HD DVD (supporting 720p and 1080i; future players will support 1080p) and Blu-ray (supporting up to 1080p). Players for both systems are expected to be backward-compatible with DVDs. However, the two formats are not compatible with each other.
The increased clarity and detail make larger screen sizes more comfortable and pleasing to watch.
Dolby Digital 5.1 sound is broadcast along with standard HDTV video signals, allowing full surround sound capabilities. (Standard broadcast television signals usually only include basic stereo audio.)
Both designs make more efficient use of electricity than SDTV designs of equivalent size, which can mean lower operating costs.
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Early systems
Main article: Analog high-definition television systems
The British 405-line black-and-white system, introduced in 1936, was the first to advertise itself as "high definition," although it was high definition only in comparison with previous mechanical and electronic television systems, and not in the sense of the term as it is used today. On the other hand, the 819-line French black-and-white television system introduced after World War II arguably was high definition in the modern sense, as it had a line count and theoretical maximum resolution considerably higher than those of the 625-line systems introduced across most of postwar Europe, and the later European 625-line color systems (PAL and SECAM).
Japan was the only country where commercial analog HDTV was launched and had some success. In other places, such as Europe, analog (HD-MAC) HDTV failed. Finally, although the United States experimented with analog HDTV (there were about 10 proposed formats), it soon moved towards a digital approach.
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Contemporary systems
Main article: List of digital television deployments by country
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Recording and compression
Main article: High-definition pre-recorded media and compression
HDTV can be recorded to D-VHS (Data-VHS), W-VHS (analog only), to an HDTV-capable digital video recorder, such as DirecTV's high-definition TiVo, a HDTV-ready Windows Media Center, or Dish Network's DVR 921, 942 or VIP622.
The massive amount of data storage required to archive uncompressed streams make it unlikely that an uncompressed storage option will appear in the consumer market soon. Realtime MPEG-2 compression of an uncompressed digital HDTV signal is also prohibitively expensive for the consumer market at this time, but should become inexpensive within several years (although this is more relevant for consumer HD camcorders than recording HDTV). Analog tape recorders with bandwidth capable of recording analog HD signals such as W-VHS recorders are no longer produced for the consumer market and are both expensive and scarce in the secondary market.
In the USA, as part of the FCC's "plug and play" agreement, cable companies are required to provide customers that rent HD set-top boxes with a set-top box with "functional" Firewire (IEEE 1394) upon request. None of the direct broadcast satellite providers have offered this feature on any of their supported boxes, but some cable TV companies have. As of July 2004, boxes are not included in the FCC mandate. This content is protected by encryption known as 5C. [2]. This encryption can prevent someone from recording content at all or simply limit the number of copies.
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Table of terrestrial HDTV transmission systems
Main characteristics of three DTTV systems Systems ATSC DVB-T ISDB-T
Source coding
Video Main Profile syntax of ISO/IEC 13818-2 (MPEG-2 – Video)
Audio ATSC Standard A/52 (Dolby AC-3) ISO/IEC 13818-2 (MPEG-2 – Layer II Audio) and Dolby AC-3 ISO/IEC 13818-7 (MPEG-2 – AAC Audio)
Transmission system
Channel coding
Outer coding R-S (207, 187, t = 10) R-S (204, 188, t = 8)
Outer interleaver 52 R-S block 12 R-S block
Inner coding rate 2/3 Trellis code PCC: rate 1/2, 2/3, 3/4, 5/6, 7/8; constraint length = 7, Polynomials (octal) = 171, 133
Inner interleaver 12 to 1 Trellis code bit-wise, frequency bit-wise, frequency, selectable time
Data randomization 16-bit PRBS
Modulation 8-VSB and 16-VSB COFDM
QPSK, 16QAM and 64QAM
Hierarchical modulation: multi-resolution constellation (16QAM and 64QAM)
Guard interval: 1/32, 1/16, 1/8 & 1/4 of OFDM symbol
Two modes: 2k and 8k FFT BST-COFDM with 13 frequency segments
DQPSK, QPSK, 16QAM and 64QAM
Hierarchical modulation: choice of three different modulations on each segment
Guard interval: 1/32, 1/16, 1/8 & 1/4 of OFDM symbol
Three modes: 2k, 4k and 8k FFT
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References
Cited references
^ Carlo Basile et al. (1995). "The U.S. HDTV standard: the Grand Alliance". IEEE Spectrum (4): 36–45.
^ 5C Digital Transmission Content Protection White Paper (pdf) (1998-07-14).
General references
United States Federal Standard 1037C
DTV channel protection ratios
DVB HDTV standard
Images formats for HDTV, article from the EBU Technical Review .
High Definition for Europe - a progressive approach, article from the EBU Technical Review .
High Definition (HD) Image Formats for Television Production, technical report from the EBU
Digital Terrestrial HDTV Broadcasting in Europe , technical report from the EBU
TV Azteca Plans HDTV Mexican Rollout
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See also
1080p, 720p, 576p, 480p, 1080i
Advanced Television Systems Committee (ATSC)
ATSC tuner
Integrated Services Digital Broadcasting
DVB (Digital Video Broadcasting)
Digital television
HDTV input and colorspace (YPbPr/YCbCr).
HD ready
SDTV (Standard Definition Television)
Ultra-High Definition Video (UHDV)
Middleware High Definition support: OpenTV HD
Arun Netravali
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External links
DTV government Resource US Government HDTV and DTV official site
HDTVExpert.co.uk UK based consumer guide to HDTV in Great Britain
HDTV Information Consumer information about HDTV
HighTech TV Glossary Common HDTV Terms and Definitions
ATSC
CDTV Canadian Digital Television official website
High Definition Forum
Linowsat List of european HDTV channels DVB-S und DVB-S2 with videobitrates
Retrieved from "http://en.wikipedia.org/wiki/High-definition_television"
Categories: ATSC | High-definition television | Film and video technology | Digital television | Consumer electronics
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