High-definition television

Un article de Vev.

High-definition television (HDTV) is a digital television broadcasting system with greater resolution than traditional television systems (NTSC, SECAM, PAL). HDTV is digitally broadcast, because digital television (DTV) requires less bandwidth if sufficient video compression is used. HDTV technology was introduced in the United States in the 1990s by the Digital HDTV Grand Alliance, a group of television companies.<ref>the Grand Alliance includes AT&T, General Instrument, MIT, Philips, Sarnoff, Thomson, and Zenith)</ref><ref name="spectrum">Modèle:Cite journal</ref>

History of high-definition television

In 1949, France launched 819 lines television, first high definition public television network (778 active lines). This 819 lines network remained operational until 1983.^{[citation needed]}

In 1958, the U.S.S.R created Трансформатор (Transformer), the first high-resolution (definition) television system capable of producing an image composed of 1,125 lines of resolution for the purpose of television conferences among military commands; as it was a military product, it was not commercialised.<ref> HDTV in the Russian Federation: problems and prospects of implementation (in Russian)

.</ref>

In 1969, Nippon Hōsō Kyōkai (NHK) first developed commercial, high-definition television, <ref> Researchers Craft HDTV's Successor

.</ref> yet, the system was not commercialized until late in the 1990s.

In 1983, the International Telecommunication Union ITU-R set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. This WP considered many views and through the 1980s served to encourage development in a number of video digital processing areas such as conversion between 30/60 and 25/50 picture rates using motion vectors that led to other outcomes. While a single standard was never finalized, a common aspect ratio of 16:9 was agreed to at the first meeting at the BBC's R & D establishment at Kingswood Warren. Initially the Japanese 5:3 ratio was considered but a proposal to widen it to 5 1/3:3 = 16:9 was accepted. The ITU-R Recommendation BT.709 includes 16:9, colorimetry and the 1080i (1,080 actively-interlaced lines of resolution) and the 1080p (1,080 progressively-scanned lines). It also included the 1440 x 1152 HDMAC scanning format. 720p formats were strongly resisted by some ITU-R members and were not standardized there. Both 1920 x 1080 and 1280 x 720p (720 progressively-scanned lines) systems for a range of frame and field rates are also defined by several SMPTE standards.

No matter how hard developers tried, and despite the over 20 different standards proposed, high definition television lacked the basics of any successful media application; that is the means of distributing it.

Early HDTV commercial experiments such as NHK's MUSE required over four times the bandwidth of a standard definition broadcast, and despite the effort made to shrink the required bandwidth into about 2 times of that of the SDTV's, it still was distributable only by satellite. In addition, recording and reproducing an HDTV signal was also a technical challenge in the early years of HDTV. Nevertheless, the first HDTV sets went on sale in the United States in 1998. However, it was not until the first decade of the new millennium that storage means of enough capacity and computer processing power for dense compression algorithms made commercial applications of HDTV affordable for consumers and profitable for TV channels or the video rental industry.

Digital HDTV was finally viable due to the evolution of TV broadcasting, where the broadcasting systems all over the world were designed from scratch to use digital means of transmission. Thus, through digital compression equipment, and the evolution of standards such as MPEG 2, H264, a single TV channel could be used either for broadcasting up to 5 TV programs of standard definition, or for broadcasting up to 2 channels of high definition.

High-definition television refers to the image resolution and, loosely, to photo- and videographic media capable of such image resolution, i.e. photographic film and digital video. Current HDTV broadcast standards are in the ATSC and DVB specifications. HDTV is capable of cinema-quality audio, because it uses the Dolby Digital (AC-3) format to support the 5.1 surround sound system.

"The FCC currently has a February 17, 2009, deadline for the transition to all digital broadcasting. On this date, all analog broadcasting will stop, and consumers will need to buy converter boxes to receive programming on their older TVs. This deadline has been pushed back several times in the last few years because of both broadcasters' and consumers' inability to meet the FCC's criteria for a successful transition to digital broadcasting. TV stations must have the equipment to send digital broadcasts, and consumers must have the TVs to receive them."<ref>http://electronics.howstuffworks.com/dtv.htm</ref>

HDTV sources

The rise in popularity of large screens and projectors has made the limitations of conventional Standard Definition TV (SDTV) increasingly evident. An HDTV compatible television set will not improve the quality of SDTV channels. To display a superior picture, high definition televisions require a High Definition (HD) signal. Typical sources of HD signals are as follows:

• Over the air with an antenna. Most cities in the US with major network affiliates broadcast over the air in HD. To receive this signal an HD tuner is required. Most newer high definition televisions have an HD tuner built in. For HDTV televisions without a built in HD tuner, a separate set-top HD tuner box can be rented from a cable or satellite company or purchased.
• Cable television companies often offer HDTV broadcasts as part of their digital broadcast service. This is usually done with a set-top box or CableCARD issued by the cable company. Alternatively one can usually get the network HDTV channels for free with basic cable by using a QAM tuner built into their HDTV or set-top box. Some cable carriers also offer HDTV on-demand playback of movies and commonly viewed shows.
• Satellite-based TV companies, such as DirecTV and Dish Network (both in North America), Sky Digital (in the UK and Ireland), Bell ExpressVu (in Canada) and NTV Plus (in Russia), offer HDTV to customers as an upgrade. New satellite receiver boxes and a new satellite dish are often required to receive HD content.
• Video game systems, such as the Xbox (NTSC only), Xbox 360, Playstation 2 (Gran Turismo 4) and Playstation 3 can output an HD signal. The Xbox Live Marketplace and Playstation Network services offers HD movies, TV shows, movie trailers, and clips for download to their respective consoles.
• Most newer computer graphics cards have either HDMI or DVI interfaces, which can be used to output images or video to an HDTV.
• Two optical disc standards, Blu-ray Disc and HD DVD, can provide enough digital storage to store hours of HD video content.DVDs look best on screens that are smaller than 36 inches, so they're not always up to the challenge of today's high-definition (HD) sets. To store and play HD movies, you need a disc that holds more information, like an HD-DVD. The basic idea behind the HD-DVD is really simple: A DVD holds about two hours of standard definition video, but an HD-DVD can hold about 48 hours.<ref>http://electronics.howstuffworks.com/hd-dvd.htm</ref>

Notation

HDTV broadcast systems are defined threefold, by:

• The number of lines in the vertical display resolution.

• The scanning system: progressive scanning (p) or interlaced scanning (i). Progressive scanning redraws an image frame (all of its lines) when refreshing each image. Interlaced scanning redraws the image field (every second line) per each image refresh operation, and then redraws the remaining lines during a second refreshing. Interlaced scanning yields greater image resolution if subject is not moving, but loses up to half of the resolution and suffers "combing" artifacts when subject is moving.

• The number of frames per second or fields per second.

The 720p60 format is 1280 × 720 pixels, progressive encoding with 60 frames per second (60 Hz). The 1080i50 format is 1920 × 1080 pixels, interlaced encoding with 50 fields per second. Sometimes interlaced fields are called half-frames, but they are not, because two fields of one frame are temporally shifted. Frame pulldown and segmented frames are special techniques that allow transmitting full frames by means of interlaced video stream.

For commercial naming of the product, either the frame rate or the field rate is dropped, e.g. a "1080i television set" label indicates only the image resolution.<ref> The HDTV Progressive Frame Rate Clarification Initiative

.</ref> Often, the rate is inferred from the context, usually assumed to be either 50 or 60, except for 1080p, which denotes 1080p24, 1080p25, and 1080p30, but also 1080p50 and 1080p60 in the future.

A frame or field rate can also be specified without a resolution. For example 24p means 24 progressive scan 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.

Standard Display Resolutions

Modèle:Contradict Image:Standard video res.svg

When resolution is considered, both the resolution of the transmitted signal and the (native) displayed resolution of a TV set are taken into account. Digital NTSC- and PAL/SECAM-like signals (480i60 and 576i50 respectively) are transmitted at a horizontal resolution 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 × 576 or 720 × 540; with an aspect ratio of 16:9 they use 1440 x 768, 1024 × 576 or 960 × 540; NTSC ones use 640 × 480 and 852 × 480 or, seldom, 720 × 540.

High-Definition Display Resolutions

High Definition usually refers to 720 vertical lines of resolution or more.

Modèle:Cleanup-section A common resolution used in HD Ready LCD TV panels is 1366 x 768<ref> 1366x768 resolution problems on HDTV, HD-Ready, and High Definition TV

.</ref> pixels instead of the ATSC Standard 1280 x 720 pixels. This is due to maximization of manufacturing yield and resolution of VGA, VRAM that comes with a 768 pixel format. Hence, LCD manufacturers adopt the 16:9 ratio compatible for the HD Ready 1080p standard. Nevertheless, every HDTV has an overscan processing chipset to fix resolution scaling and color rendering, eg LG XD Engine, SONY BRAVIA Engine. Only when viewing 1080i/1080p HD contents under HD Ready 1080p where there is true pixel-for-pixel reproduction, and for HD ready LCD TV, do some signals undergo a scaling process which results in a 3-5% loss of picture.

Standard frame or field rates

• 23.976p (allow easy conversion to NTSC)
• 24p (cinematic film)
• 25p (PAL, SECAM DTV progressive material)
• 30p (29.97p in drop frame) (NTSC DTV progressive material)
• 50p (PAL, SECAM DTV progressive material)
• 60p (59.94p in drop frame) (NTSC DTV progressive material)
• 50i (PAL & SECAM)
• 60i (59.94i in drop frame) (NTSC, PAL-M)

Broadcast station format considerations

At the least, HDTV has twice the linear resolution of standard-definition television (SDTV), thus showing greater detail than either analog television or regular DVD. The technical standards for broadcasting HDTV also handle the 16:9 aspect ratio images without using letterboxing or anamorphic stretching, thus increasing the effective image resolution.

The optimum format for a broadcast depends upon the type of videographic recording medium used and the image's characteristics. The field and frame rate should match the source and the resolution. A very high resolution source may require more bandwidth than available in order to be transmitted without loss of fidelity. The lossy compression that is used in all digital HDTV storage and transmission systems will distort the received picture, when compared to the uncompressed source.

Types of medium

The high resolution photographic film used for cinema projection is exposed at the rate of 24 frames per second. Depending upon available bandwidth and the amount of detail and movement in the image, the optimum format for video transfer is either 720p24 or 1080p24. When shown on television in PAL system countries, film must be projected at the rate of 25 frames per second by accelerating it by 4.1 per cent. In NTSC standard countries, the projection rate is 30 frames per second, a using a technique called 3:2 pull-down. One film frame is held for three video fields (1/20 of a second), and the next is held for two video fields (1/30 of a second) and then the process is repeated, thus achieving the correct film projection rate with two film frames shown in 1/12 of a second. Modèle:Cf.

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. Modèle:Seealso

Non-cinematic HDTV video recordings are recorded in either the 720p or the 1080i format. The format used is set by the broadcaster (if for television broadcast). In general, 720p is more accurate with fast action, because it progressively scans frames, instead of the 1080i, which uses interlaced fields and thus might degrade the resolution of fast images.

720p is used more for Internet distribution of high-definition video, because computer monitors progressively scan; 720p video has lower storage-decoding requirements than either the 1080i or the 1080p.

List of stations

• In Australia, the 576p50 format is also considered a HDTV format, as it has higher vertical resolution through the use of progressive scanning. When Australia started DVB-T in 2001 several networks broadcast high-definition in a 576p format as this could give better quality on 50Hz scanning CRT TVs and was not as demanding on MPEG-2 bit-rate. Now that flat-screens are predominating and these have an interlace to progressive scan conversion there is little difference in picture quality. Also MPEG-2 encoders have improved so the more conventional 720p and 1080i formats are now used. Technically, the 576p format is internationally defined as Enhanced-definition television and many DVD players can provide a 576p signal usually on HDMI outputs.

• In North America, Fox, My Network TV (both owned by the News Corporation), ABC, and ESPN (ABC and ESPN are both owned by Disney) currently broadcast 720p content. NBC, Universal HD (both owned by the NBC Universal subsidiary of General Electric and Vivendi), CBS, The CW (co-owned by CBS and Time Warner), HBO (owned by Time Warner), Showtime (owned by CBS), Starz!, MOJO HD, HDNet ,TNT(owned by Time Warner), CNN (also owned by Time Warner), and Discovery HD Theater currently broadcast 1080i content. In Canada, virtually all over-the-air HD stations broadcast 1080i, as do most cable specialty channels.

• In Singapore, MediaCorp TV HD5 is Singapore's first over-the-air HDTV channel, simulcasting HD version of Channel 5 programming in 1080i. It is the first terrestrial broadcast HD channel in South-East Asia and also first in the world to use MPEG4/AVC compression.<ref> Southeast Asia's first HD channel, HD5 launches 11 Nov 2007

.</ref>

• In the United Kingdom on Sky Digital, there are BBC HD, Sky One HD, Sky Arts HD, Sky Movies HD1 & 2, Sky Sports HD1,2 & X, Discovery HD, National Geographic Channel HD, The History Channel HD & Sky Box Office HD1 & 2. With MTV HD, FX HD, Living HD Rush HD, Ultra HD & Eurosport HD to come in the near future. BBC HD is also available on Virgin Media. The BBC Trust has given provisional approval for a BBC HD channel, which would be broadcast satellite, cable and DTT.
  • Public consultation on the Trust's provisional conclusions on the proposed BBC HD service is open until 23 October 2007.

• In Brazil all 5 major TV networks (Band, Rede Globo, Rede Record, RedeTV! and SBT) and the public television started to broadcast HDTV (1080i) in December 2007. Brazil uses a mixture of the japanese HDTV system with Brazilian tecnology called SBTVD.

Technical details

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 trialing such a system via satellite broadcast, which will save considerable bandwidth compared to MPEG-2 systems. Some German broadcasters already use MPEG-4 AVC together with DVB-S2 (Pro 7, Sat.1 and Premiere). Although MPEG-2 is more widely used at present, it seems likely that in the future all European HDTV may be MPEG-4 AVC, and Norway, which is currently in the progress of implementing digital television broadcasts, is using MPEG-4 AVC for present SD Digital as well as for future HDTV on terrestrial broadcasts. In parts of Sweden the standard is already in use for HDTV terrestrial broadcasting, reaching about 25-30% of the population.

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, in which each pixel's height equals its width. New HD compression and recording formats such as HDV use rectangular pixels to save bandwidth and to open HDTV acquisition for the consumer market. For more technical details see the articles on HDV, ATSC, DVB, and ISDB.

Television studios as well as production and distribution facilities, use HD-SDI SMPTE 292M interconnect standard (a nominally 1.485 Gbit/s, 75-ohm serial digital interface) to route uncompressed HDTV signals. The native bitrate of HDTV formats cannot be supported by 6-8 MHz 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 Cinealta F23 & 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.

Advantages of HDTV expressed in non-technical terms

Modèle:Unreferenced Modèle:Confusing Modèle:Original research

High-definition television (HDTV) yields a better-quality image than does standard television, because it has a greater number of lines of resolution. Because the signal is a digital signal, it produces neither a snowy nor pale image from a weak signal or signal interference effects, such as herringbone patterns, or vertical rolling. Image colours are more realistic, because of the greater bandwidth. The visual information is some 2-5 times sharper because the gaps between the scan lines are narrower or invisible to the naked eye. Television content photographed and preserved on 35 mm film can be viewed at nearly its original resolution.

The lower-case "i" appended to the numbers denotes interlaced; the lower-case "p" denotes progressive. The interlaced scanning method, the 1,080 lines of resolution are divided into two, the first 540 lines are painted on a frame, the second 540 lines are painted on a second frame, reducing the bandwidth and increasing frame rate to 50-60 frames per second. The progressive scanning method simultaneously displays all 1,080 lines of resolution at 60 frames per second, on a greater bandwidth. (See: An explanation of HDTV numbers and laymen's glossary)

Often, the broadcast HDTV video signal soundtrack is Dolby Digital 5.1 surround sound, enabling full, surround sound capabilities, while STBC television signals include either monophonic or stereophonic audio, or both. Stereophonic broadcasts can be encoded with Dolby Surround audio signal.

Disadvantages of HDTV expressed in non-technical terms

Modèle:Confusing

In practice, the best possible HD quality is not usually achieved. The main problem is that many operators do not follow HDTV specifications fully. They may use slower bitrates or lower resolution to pack more channels within the limited bandwidth.<ref> DirecTV HD Image Quality

.</ref> The operators may use format that is different from the original programming, introducing generation loss artifacts in the process of re-encoding.<ref> DirecTV's HD future is MPEG-4

.</ref> Also, image quality may be lost if the television is not properly connected to the input device or not properly configured for the input's optimal performance, which may be difficult because of customer confusion regarding connections.

As high-definition video broadcasts are digital, the disadvantages of digital video broadcasting also apply here. For example, digital video responds differently to analogue video when subject to interference. As opposed to a lower-quality signal one gets from interference in an analogue television broadcast, interference in a digital television broadcast will freeze, skip, or display "garbage" information. Broadcasters may aggressively compress video to save bandwidth and therefore broadcast more channels - this compression manifests itself as reduced video quality.

In order to view HDTV broadcasts, viewers may have to upgrade their TVs, incurring household expense in the process. Adding a new aspect ratio makes for consumer confusion if their display is capable of one or more ratios but must be switched to the correct one by the user. Traditional standard definition TV shows and feature films (mostly movies from before 1953) originally filmed in the standard 4:3 ratio, when displayed correctly on an HDTV monitor, will have empty display areas to the left and right of the image. Many consumers aren't satisfied with this unused display area and choose instead to distort their standard definition shows by stretching them horizontally to fill the screen, giving everything a too-wide or not-tall-enough appearance. Alternately, they'll choose to zoom the image which removes content that was on the top and bottom of the original TV show.<ref>http://www.answers.com/topic/hdtv-display-modes?cat=technology</ref>

As of 2007, broadcasters may demand, or cable-television operators may elect, to place HD signals in a premium band that requires higher cable fees. That some satellite companies offer the local HD channels as a service at additional cost (transmission comes from satellite) suggests to some broadcasters that on-air broadcasts of local HD signals must be a premium service to subscribers. Viewers may be denied some television channels that they expected, be allowed only access to the non-digital, and obviously sub-standard non-digital signal, or have to install an antenna to receive the digital broadcasts. Such issues more entail economic and legal disputes than they entail technology.

Another disadvantage of HDTV compared to traditional television has been consumer confusion stemming from the different standards and resolutions, such as 1080i, 1080p, and 720p. Complicating the matter have been the changes in television connections from component video, to DVI, then to HDMI. Finally, the HD-DVD vs. Blu-ray Disc high definition storage format war engenders even more animosity for consumers. The confusion has led to slower uptake of the technology as many people wait to see what becomes the "ultimate" de-facto standard.

Early systems

Main article: Analog high-definition television systems

The term high definition described the television systems of the 1930s and 1940s beginning with the British 405-line black-and-white system, introduced in 1936; however, it and the American 525-line NTSC system established in 1941, were high definition in comparison with previous mechanical and electronic television systems. Today, the American 525-line NTSC system and the European 625-line PAL and SECAM systems are standard definition television, whereas the post–WWII French 819-line black-and-white system, was high definition in the contemporary sense, it required more bandwidth and was discontinued in 1986, a year after the final British 405-line broadcast.

Japan is the only country with successful commercial analog HDTV, known as "Hi-vision", featuring a 5:3 aspect ratio screen with 1,125 interlaced lines (1,035 active lines) at the rate of 60 fields per second. Elsewhere, in Europe, analog 1,125-line HD-MAC television failed in its test broadcasts in the early 1990s.

Contemporary systems

Main article: Large-screen television technology

Besides an HD-ready television set, other equipment is needed to view HD television. Cable-ready TV sets can display HD content without using an external box. They have a card slot for inserting a CableCARD.<ref> HDTV information

.</ref>.

High-definition image sources include terrestrial broadcast, direct broadcast satellite, digital cable, high definition discs (BD and HD DVD), internet downloads and the latest generation of video game consoles.

Main article: List of digital television deployments by country

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 a HDTV-capable digital video recorder (for example DirecTV's high-definition Digital video recorder, Sky HD's set-top box, Dish Network's VIP 622 or VIP 722 high-definition Digital video recorder receivers, or TiVo's Series 3 or HD recorders), or an HDTV-ready HTPC. Some cable boxes are capable of receiving or recording two broadcasts at a time in HDTV format, and HDTV programming, some free, some for a fee, can be played back with the cable company's on-demand feature. 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 United States, 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.<ref> 5C Digital Transmission Content Protection White Paper

 (pdf)
 (1998-07-14)
   

.</ref> This encryption can prevent duplication of content or simply limit the number of copies permitted, thus effectively denying most if not all fair use of the content.

Table of terrestrial HDTV transmission systems

TV resolution

Modèle:TV resolution

References

See also

• 480p, 576p, 720p, 1080i, 1080p
• 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)
• High-definition television in the United Kingdom
• Freesat
• High-definition television in the United States
• HDTV Blur

External links

• US Government HDTV and DTV official site
• Canadian Radio-television and Telecommunications Commission
• CEA'S HDTV Guide

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