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=== Rise of digital compression ===
=== Rise of digital compression ===
Since 1972 [[International Telecommunication Union]]'s radio telecommunications sector ([[ITU-R]]) ITU-R has been working on creating a global recommendation for Analogue HDTV. These recommendations however did not fit in the broadcasting bands which could reach home users. The standardization of [[MPEG-1]] in 1993 also lead to acceptation of recommendations ITU-R BT.709. In anticipation of these standards the DVB organisation was formed, an alliance of broadcasters, consumer electronics manufacturers and regulatory bodies. The DVB develops and agrees specification which are formally standardised by ETSI.
Since 1972 [[International Telecommunication Union]]'s radio telecommunications sector ([[ITU-R]]) ITU-R has been working on creating a global recommendation for Analogue HDTV. These recommendations however did not fit in the broadcasting bands which could reach home users. The standardization of [[MPEG-1]] in 1993 also lead to acceptation of recommendations ITU-R BT.709<ref>{{cite web|url=http://www.itu.int/ITU-R/index.asp?category=information&link=hdtv-25&lang=en|title=High definition television comes of age thanks to ITU}}</ref>. In anticipation of these standards the DVB organisation was formed, an alliance of broadcasters, consumer electronics manufacturers and regulatory bodies. The DVB develops and agrees specification which are formally standardised by ETSI<ref>{{cite web|url=http://www.dvb.org/about_dvb/history/|title=History of the DVB Project}}</ref>.


DVB created first the standard for [[DVB-S]] digital satellite TV, [[DVB-C]] digital cable TV and [[DVB-T]] digital terrestrial TV. These broadcasting systems can be used for both SDTV and HDTV. In the USA the Grand Alliance proposed [[ATSC Standards|ATSC]] as the new standard for SDTV and HDTV. Both ATSC and DVB were based on the MPEG-2 standard. The [[DVB-S2]] standard is based on the newer and more efficient [[H.264/MPEG-4 AVC]] compression standards. Common for all DVB standards is the use of highly efficient modulation techniques for further reducing bandwidth, and foremost for reducing receiver-hardware and antenna requirement.
DVB created first the standard for [[DVB-S]] digital satellite TV, [[DVB-C]] digital cable TV and [[DVB-T]] digital terrestrial TV. These broadcasting systems can be used for both SDTV and HDTV. In the USA the Grand Alliance proposed [[ATSC Standards|ATSC]] as the new standard for SDTV and HDTV. Both ATSC and DVB were based on the MPEG-2 standard. The [[DVB-S2]] standard is based on the newer and more efficient [[H.264/MPEG-4 AVC]] compression standards. Common for all DVB standards is the use of highly efficient modulation techniques for further reducing bandwidth, and foremost for reducing receiver-hardware and antenna requirement.

Revision as of 10:47, 19 June 2009

High-definition television (or HDTV) is a digital television broadcasting system with higher resolution than traditional television systems (standard-definition TV, or SDTV). HDTV is digitally broadcast; the earliest implementations used analog broadcasting, but today digital television (DTV) signals are used, requiring less bandwidth due to digital video compression.

Projection screen in a home theater, displaying a high-definition television image.

History of high-definition television

Further information: [[:Analog high-definition television system]]

The term high definition once described a series of television systems originating from the late 1930s, however, these systems were only "high definition" when compared to earlier systems that were based on mechanical systems with as few as 30 lines of resolution.

The British high definition TV service started trials in August 1936 and a regular service in November 1936 using both the Baird 240 line and Marconi-EMI 405 line systems. The Baird system was discontinued in February 1937. In 1938 France followed with their own 441 line system, which was also used by a number of other countries. The US NTSC system joined in 1939. In 1949 France introduced an even higher resolution standard at 819 lines, a system that would be high definition even by today's standards, but it was monochrome only. All of these systems used interlacing and a 4:3 aspect ratio except the 240 line system which was progressive (actually described at the time by the technically correct term of 'sequential') and the 405 line system which started as 5:4 and later changed to 4:3. The 405 line system adopted the (at that time) revolutionary idea of interlaced scanning to overcome the flicker problem of the 240 line with its 25 Hz frame rate. The 240 line system could have doubled its frame rate but this would have meant that the transmitted signal would had doubled in bandwidth, an unacceptable option.

Color broadcasts started at similar "high" resolutions, first with the US's NTSC color system in 1953, which was compatible with the earlier B&W systems and therefore had the same 525 lines of resolution. European standards did not follow until the 1960s, when the PAL and SECAM colour systems were added to the monochrome 625 line broadcasts.

Since the formal adoption of Digital Video Broadcasting's (DVB) widescreen HDTV transmission modes in the early 2000s the 525-line NTSC (and PAL-M) systems as well as the European 625-line PAL and SECAM systems are now regarded as "standard definition" television systems. In Australia, the 625-line digital progressive system (with 576 active lines) is officially recognized as high definition.[1]

Analog systems

In 1958, the Soviet Union created Тransformator (Russian: 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 commercialized.[2]

In 1969, the Japanese state broadcaster NHK first developed consumer high-definition television with a 5:3 aspect ratio, a slightly wider screen format than the usual 4:3 standard.[3] The system, known as Hi-Vision or MUSE after its Multiple sub-nyquist sampling Encoding system for encoding the signal, required about twice the bandwidth of the existing NTSC system but provided about four times the resolution. Satellite test broadcasts started in 1989, with regular testing starting in 1991 and regular broadcasting of BS-9ch commenced on 25 November 1994, which featured commercial and NHK programming.

In 1981, the MUSE system was demonstrated for the first time in the United States. It had the same 5:3 aspect ratio as the Japanese system.[4] Upon visiting a demonstration of MUSE in Washington, US President Ronald Reagan was most impressed and officially declared it "a matter of national interest" to introduce HDTV to the USA.[5]

Several systems were proposed as the new standard for the USA, including the Japanese MUSE system, but all were rejected by the FCC because of their higher bandwidth requirements. At the same time that the high definition systems were being studied, the number of television channels was growing rapidly and bandwidth was already a problem. A new standard had to be radically efficient, needing less bandwidth for HDTV than the existing NTSC standard for SDTV.

Rise of digital compression

Since 1972 International Telecommunication Union's radio telecommunications sector (ITU-R) ITU-R has been working on creating a global recommendation for Analogue HDTV. These recommendations however did not fit in the broadcasting bands which could reach home users. The standardization of MPEG-1 in 1993 also lead to acceptation of recommendations ITU-R BT.709[6]. In anticipation of these standards the DVB organisation was formed, an alliance of broadcasters, consumer electronics manufacturers and regulatory bodies. The DVB develops and agrees specification which are formally standardised by ETSI[7].

DVB created first the standard for DVB-S digital satellite TV, DVB-C digital cable TV and DVB-T digital terrestrial TV. These broadcasting systems can be used for both SDTV and HDTV. In the USA the Grand Alliance proposed ATSC as the new standard for SDTV and HDTV. Both ATSC and DVB were based on the MPEG-2 standard. The DVB-S2 standard is based on the newer and more efficient H.264/MPEG-4 AVC compression standards. Common for all DVB standards is the use of highly efficient modulation techniques for further reducing bandwidth, and foremost for reducing receiver-hardware and antenna requirement.

In 1983, the International Telecommunication Union's radio telecommunications sector (ITU-R) set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. One of the thornier issues concerned a suitable frame/field refresh rate, with the world already strongly demarcated into two camps, 25/50Hz and 30/60Hz, related by reasons of picture stability to the frequency of their mains electrical supplies.

The WP considered many views and through the 1980s served to encourage development in a number of video digital processing areas, not least conversion between the two main frame/field rates using motion vectors, which led to further developments in other areas. While a comprehensive HDTV standard was not in the end established, agreement on the aspect ratio was achieved.

Initially the existing 5:3 aspect ratio had been the main candidate, but due to the influence of widescreen cinema, the aspect ratio 16:9 (1.78) eventually emerged as being a reasonable compromise between 5:3 (1.67) and the common 1.85 widescreen cinema format. (It has been suggested that the 16:9 ratio was chosen as being the geometric mean of 4:3, Academy ratio, and 2.35:1, the widest cinema format in common use, in order to minimize wasted screen space when displaying content with a variety of aspect ratios.)

An aspect ratio of 16:9 was duly agreed at the first meeting of the WP at the BBC's R & D establishment in Kingswood Warren. The resulting ITU-R Recommendation ITU-R BT.709-2 ("Rec. 709") includes the 16:9 aspect ratio, a specified colorimetry, and the scan modes 1080i (1,080 actively-interlaced lines of resolution) and 1080p (1,080 progressively-scanned lines). The current BBC freeview trials of HD use MBAFF, which contains both progressive and interlaced content in the same encoding.

It also includes the alternative 1440 x 1152 HDMAC scan format. (According to some reports, a mooted 720p format (720 progressively-scanned lines) was viewed by some at the ITU as an "enhanced" television format rather than a true HDTV format,[8] and so was not included, although 1920x1080 and 1280x720p systems for a range of frame and field rates were defined by several US SMPTE standards.)

Demise of analog HD systems

However, even that limited standardization of HDTV did not lead to its adoption, principally for technical and economic reasons. Early HDTV commercial experiments such as NHK's MUSE required over four times the bandwidth of a standard-definition broadcast, and despite efforts made to shrink the required bandwidth down to about two times that of SDTV, it was still only distributable by satellite with one channel shared on a daily basis between seven broadcasters. In addition, recording and reproducing an HDTV signal was a significant technical challenge in the early years of HDTV. Japan remained the only country with successful public broadcast analog HDTV. Digital HDTV broadcasting started in 2000 in Japan, and the analog service ended in the early hours of 1 October 2007.

In Europe, analogue 1,250-line HD-MAC test broadcasts were performed in the early 1990s, but did not lead to any established public broadcast service.

Inaugural HDTV broadcast in the United States

HDTV technology was introduced in the United States in the 1990s by the Digital HDTV Grand Alliance, a group of television companies and MIT.[9][10] Field testing of HDTV at 199 sites in the United States was completed August 14, 1994.[11] The first public HDTV broadcast in the United States occurred on July 23, 1996 when the Raleigh, North Carolina television station WRAL-HD began broadcasting from the existing tower of WRAL-TV south-east of Raleigh, winning a race to be first with the HD Model Station in Washington, D.C., which began broadcasting July 31, 1996.[12][13][14] The American Advanced Television Systems Committee (ATSC) HDTV system had its public launch on October 29, 1998, during the live coverage of astronaut John Glenn's return mission to space on board the Space Shuttle Discovery.[15] The signal was transmitted coast-to-coast, and was seen by the public in science centers, and other public theaters specially equipped to receive and display the broadcast.[15] The broadcast was made possible by the Harris Corporation, which sponsored the equipment necessary for transmitting and receiving the broadcast.[15][16]

First regular European HDTV broadcasts

Although HDTV broadcasts had been demonstrated in Europe since the early 1990s, the first regular broadcasts started on January 1, 2004 when Euro1080 launched the HD1 channel with the traditional New Year concert from Vienna. Test transmissions had been active since the IBC exhibition in September 2003, but the New Year's Day broadcast marked the official start of the HD1 channel, and the start of HDTV in Europe.[17]

Euro1080, a division of the Belgian TV services company Alfacam, broadcast HDTV channels to break the pan-European stalemate of "no HD broadcasts mean no HD TVs bought means no HD broadcasts..." and kick-start HDTV interest in Europe.[18]

The HD1 channel was initially free-to-air and mainly comprised sporting, dramatic, musical and other cultural events broadcast with a multi-lingual soundtrack on a rolling schedule of 4 or 5 hours per day.

These first European HDTV broadcasts used the 1080i format with MPEG-2 compression on a DVB-S signal from SES Astra's 1H satellite at Europe's main DTH Astra 19.2°E position. Euro1080 transmissions later changed to MPEG-4/AVC compression on a DVB-S2 signal in line with subsequent broadcast channels in Europe.

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), Premiere (in Germany), TeleDunya, Sky Digital and freesat (in the UK and Ireland), Bell TV and Shaw Direct (both in Canada), Canal Digitaal (in the Netherlands), Canal Digital and Viasat (both in Norway, Sweden and Denmark), Cyfra+, Cyfrowy Polsat and n (in Poland), NTV Plus (in Russia) and Digit-Alb (in Albania), offer HDTV to customers as an upgrade. New satellite receiver boxes are usually required to receive HD content.
  • Video game systems, such as the PlayStation 3 and Xbox 360, and digital set-top boxes such as the Apple TV, and the Netgear Digital Entertainer, can output an HD signal. The Xbox Live Marketplace, iTunes Music Store, and PlayStation Network services offer HD movies, TV shows, movie trailers, and clips for download, but generally at lower bitrates than a Blu-ray Disc.
  • Most newer computer graphics cards have either HDMI or DVI interfaces, which can be used to output images or video to an HDTV.
  • Almost all computer graphics cards have standard SVGA jacks which can be used to output images or video to an HDTV's "PC Input" jack.
  • The optical disc standard Blu-ray Disc (25GB-50GB) can provide enough digital storage to store up to 10 hours of HD video content, depending on encoder settings.[19]

Notation

HDTV broadcast systems are identified with three major parameters:

  • Frame size in pixels is defined as number of horizontal pixels x number of vertical pixels, for example 1280 x 720 or 1920 x 1080. Often the number of horizontal pixels is implied from context and is omitted.
  • Scanning system is identified with the letter p for progressive scanning or i for interlaced scanning.
  • Frame rate is identified as number of video frames per second. For interlaced systems an alternative form of specifying number of fields per second is often used. Recently the uniform notation of specifying number of frames per second both for progressive and interlaced video has become increasingly popular.[20]

If all three parameters are used, they are specified in the following form: [frame size][scanning system][frame rate]. Often, one parameter can be dropped if its value is implied from context. In this case the remaining numeric parameter is specified first, followed by the scanning system.

For example, 1920x1080p25 identifies progressive scanning format with 25 frames per second, each frame being 1920 pixels wide and 1080 pixels high. The 1080i25 or 1080i50 notation identifies interlaced scanning format with 50 fields(25 frames) per second, each frame being 1920 pixels wide and 1080 pixels high. The 1080i30 or 1080i60 notation identifies interlaced scanning format with 60 fields (30 frames) per second, each frame being 1920 pixels wide and 1080 pixels high. The 720p60 notation identifies progressive scanning format with 60 frames per second, each frame being 720 pixels high, 1280 pixels horizontally are implied.

While 50Hz systems have only three scanning rates: 25i, 25p and 50p, 60Hz systems operate with much wider set of frame rates: 23.98p, 24p, 29.97i/59.94i, 29.97p, 30p, 59.94p and 60p. In the days of standard definition television, the fractional rates were often rounded up to whole numbers, like 23.98p was often called 24p, or 59.94i was often called 60i. High definition television allows using both fractional and whole rates, therefore strict usage of notation is required. Nevertheless, 29.97i/59.94i is almost universally called 60i, likewise 23.98p is called 24p.

For commercial naming of a product, the frame rate is often dropped and is implied from context, e.g. a "1080i television set". A frame 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. Most HDTV systems support resolutions and frame rates defined either in the ATSC table 3, or in EBU specification. The most common are noted below.

Standard display resolutions

Standard Definition usually refers to 480 horizontal lines of resolution.

Resolution (W×H) Active Frame (W×H) Canonical Name(s) Pixels (Advertised Megapixels) Display Aspect Ratio (X:Y) Pixel Aspect Ratio - Standard "4:3" (X:Y) Pixel Aspect Ratio - Widescreen "16:9" (X:Y) Description
ITU-R BT.601 MPEG-4 ITU-R BT.601 MPEG-4
720×480 710.85×480 480i/p 345,600 (0.3) 4:3 4320:4739 10:11 5760:4739 40:33 Used for 525-line/ (60 * 1000/1001) Hz video, e.g. NTSC-M
720×576 702×576 576i/p 414,720 (0.4) 4:3 128:117 12:11 512:351 16:11 Used for 625-line/50 Hz video, e.g. PAL-I

When resolution is considered, both the resolution of the transmitted signal and the (native) displayed resolution of a TV set are taken into account. Most HDTV sets contain video scalers and will "upscale" or "upconvert" the transmitted signal to that of the set's native format.

Sometimes the progressive versions of these video formats are referred to as EDTV, or "Enhanced Definition Television." This is slightly misleading, for although a progressive frame contains double the image information as that of an interlaced frame, Standard Definition is already capable of displaying progressive frames, for example in MPEG video with the appropriate "Progressive" flag set. Despite this, 480p/576p signals are not typically broadcast, an example of such would be Australia's SBS HD channel, broadcast in 576p.

High-definition display resolutions

High Definition usually refers to 720 lines of video format resolution or more displayed in a horizontal fashion from top to bottom.

Video Format Supported Native Resolution (W×H) Pixels (Advertised Megapixels) Aspect Ratio (X:Y) Description
Image Pixel
720p
1280×720 		1024×768
XGA 		786,432 (0.8) 16:9 4:3 Typically a PC resolution XGA; also a native resolution on many entry-level plasma dipslays with non-square pixels.
1280×720
 921,600 (0.9) 16:9 1:1 Typically one of the PC resolutions on WXGA, also used for 750-line video, as defined in SMPTE 296M, ATSC A/53, ITU-R BT.1543, Digital television, DLP and LCOS projection HDTV displays.
1366×768
WXGA 		1,049,088 (1.0) 683:384
(Approx 16:9) 		1:1
Approx 		Typically a TV resolution WXGA; also exists as a standardized HDTV displays as (HD Ready 720p,1080i), TV that used on LCD HDTV displays.
1080i
1920×1080 		1280×1080 1,382,400 (1.4) 32:27
(Approx 16:9) 		3:2 Non-standardized "HD Ready", TV. Used on HDTVs with non-square pixels.
1080p
1920×1080 		1920×1080
 2,073,600 (2.1) 16:9 1:1 A standardized HDTV displays as (HD Ready 1080p) TV, that used on high-end LCD and Plasma HDTV displays. Used for 1125-line video, as defined in SMPTE 274M, ATSC A/53, ITU-R BT.709.

A common native resolution used in HD Ready LCD TV panels is 1366 x 768[21] 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 video 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.

Video Format Supported Screen Resolution (W×H) Pixels (Advertised Megapixels) Aspect Ratio (X:Y) Description
Image Pixel
720p
1280×720 		1248×702
Clean Aperture 		876,096 (0.9) 16:9 1:1 Used for 750-line video with raster artifact/overscan compensation, as defined in SMPTE 296M.
1080p
1920×1080 		1888×1062
Clean Aperture 		2,001,280 (2.0) 16:9 1:1 Used for 1125-line video with faster artifact/overscan compensation, as defined in SMPTE 274M.
1080i
1920×1080 		1440×1080
HDCAM/HDV 		1,555,200 (1.6) 4:3 4:3:1 Used for anamorphic 1125-line video in the HDCAM and HDV formats introduced by Sony and defined (also as a luminance subsampling matrix) in SMPTE D11.

It should be noted that the numbers used for "HD-Ready" image resolutions do not constitute acceptable 750- or 1125-line video signals in most standards-compliant hardware; in this respect terms such as "720p" and "1080p" are mostly used for advertising, though that does not necessarily mean that HD-Ready TVs labeled in this manner are incapable of accepting those formats as input.

Additionally, the "Clean Aperture" numbers are almost always contained within the frames of their respective "Production Aperture" numbers (e.g., a 1888×1062 rectangle would be contained within a 1920×1080 frame). This is to maintain compatibility with analog signals, which can often become distorted close to the edge of the frame. It also increases the chance that a digital signal being played on overscan-enabled equipment will display the entire picture visibly.

Standard frame or field rates

  • 23.976 FPS (film-looking frame rate compatible with NTSC clock speed standards)
  • 24 FPS (international film and NTSC high definition material)
  • 25 FPS (PAL, SECAM film, standard definition, and high definition material)
  • 29.97 FPS (NTSC standard definition material)
  • 50 FPS (PAL & SECAM high definition material))
  • 60 FPS (NTSC high definition material)

All flavors are compatible with Progressive or Interlaced scanning.

Broadcast station format considerations

Close-up view
HDTV resolution SDTV resolution

At a minimum, 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 media

Standard 35 mm photographic film used for cinema projection has higher resolution than HDTV systems, and is exposed and projected at a rate of 24 frames per second. To be shown on television in PAL-system countries, cinema film is scanned at the TV rate of 25 frames per second, causing an acceleration of 4.1 percent, which is generally considered acceptable. In NTSC-system countries, the TV scan rate of 30 frames per second would cause a perceptible acceleration if the same were attempted, and the necessary correction is performed by a technique called 3:2 pull-down: over each successive pair of film frames, one 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), giving a total time for the two frames of 1/12 of a second and thus achieving the correct average film frame rate.

See also: Telecine

Non-cinematic HDTV video recordings intended for broadcast are typically recorded either in 720p or 1080i format as determined by the broadcaster. 720p is commonly used for Internet distribution of high-definition video, because all computer monitors operate in progressive-scan mode. 720p also imposes less strenuous storage and decoding requirements compared to both 1080i and 1080p. 1080p is usually used for Blu-ray Disc.

List of stations

Technical details

One of the first DVB-S2 tuner cards.
Networked dual-tuner for ATSC and QAM

Current HDTV broadcast standards include ATSC (North America, parts of Central America and South Korea), DVB (Europe, Australia, New Zealand, parts of Asia, South America and Africa) and ISDB-T (Japan, Brazil,Peru). HDTV signals and colorimetry are defined by Rec. 709.

Digital compression methods such as MPEG-2 and H.264/MPEG-4 AVC allow the bandwidth of a single analog TV channel (6 MHz in the US) to carry up to 5 standard-definition or up to 2 high-definition digital TV channels instead. Initially MPEG-2 was 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. The Chinese HDTV system uses an Intellectual Property free MPEG-2 codec that may have some coding interoperability issues with current DVB codecs

The introduction of DVB-S2 has aided the use of the more bandwidth-efficient H.264/MPEG-4 AVC compression both for HDTV and next generation SD broadcasts by satellite. The majority of HDTV 2 is restricted to a handful of channels only.[22]

Some broadcasters are still using DVB-S (with MPEG-4) because their HD channels share transponders with existing SD channels broadcasting to legacy receivers without DVB-S2 capabilities (eg BBC HD on Astra 2D).

For terrestrial HDTV, some services already in operation (such as in France) are using MPEG-2 with DVB-T but the establishment of DVB-T2[23] has meant that most European terrestrial HDTV is likely to use MPEG-4 and some countries, such as the UK,[24] have committed future plans to this standard.

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 but the ISDB-Tb used primarily in Brasil uses HE-AAC that is more flexible than AC-3 and lower royalty fees.

Television studios as well as production and distribution facilities, use the 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.

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. Brasil opted to upgrade the ISDB-T Japanese standard to H.264/MPEG-4 AVC in the video compression and HE-AAC for audio compression because Dolby is not open and the royalty fees are more expensive than that of H.264 and renamed the upgraded standard to ISDB-Tb that now became the International ISDB-T standard.

Advantages of HDTV expressed in non-technical terms

High-definition television (HDTV) yields a better-quality image than standard television does, because it has a greater number of lines of resolution. The visual information is some 2-5 times sharper because the gaps between the scan lines are narrower or invisible to the naked eye. The larger the size of the television the HD picture is viewed on, the greater the improvement in picture quality. On smaller televisions there may be no noticeable improvement in picture quality.

The lower-case "i" appended to the numbers denotes interlaced; the lower-case "p" denotes progressive. With the interlaced scanning method, the 1,080 lines of resolution are divided into pairs. The first 540 alternate lines are painted on a frame and then the second 540 lines are painted on a second frame. The progressive scanning method simultaneously displays all 1,080 lines on every frame, requiring a greater bandwidth.

Disadvantages of HDTV expressed in non-technical terms

Limitations to picture quality

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 lower bitrates or smaller resolution to pack more channels within the limited bandwidth, reducing video quality.[25] The operators may use a format that is different from the original programming, introducing artifacts in the process of re-encoding.[26] 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. Also, some HDTV broadcasters intentionally distort the aspect ratio of program material for convenience, for example, when horizontally stretching the 4:3 source used for the standard-definition version of their channel up to 16:9 for the HDTV version of their channel, resulting in an image where objects are too "short and fat". The proper approach (properly obtaining a true 16:9 version of the source material instead of horizontally-stretching the 4:3 version) is not always used. This aspect-skewing "shortcut to 16:9" has been observed on several so-called "16:9" major HDTV cable channels in the USA as recently as June 2009 with the FOOD Network HD channel and HGTV HD channel being two examples.

Connector cables

Appropriate cabling must be used. Either HDMI, DVI, component video or VGA cables must be used to support a high-definition signal. For instance, if composite or S-Video cables are used for connections from a cable box or satellite dish then only an SDTV quality picture will be seen. Component video cables are RCA cables that are color coded for proper signal. They consist of three video cables (green, blue, and red), two audio cables (red and white), and they carry an analog signal. HDMI cables carry all the video and audio in one cable using a digital signal.

Signal quality

As high-definition video broadcasts are digital, the disadvantages of digital video broadcasting also apply. For example, digital video responds differently from analog video when subject to interference. Unlike in analog television broadcasting, in which interference causes only gradual image and sound degradation, interference in a digital television broadcast will freeze, skip, or display "garbage" information. This is often called the "cliff effect" where one either gets a perfect picture or none at all. The quality of the antenna is especially important, especially in DVB-T which is extremely sensitive to impulse noise from electrical appliances or automobiles and may require the installation of fully shielded antenna cables in order to successfully receive a picture.

Early ATSC receivers were very sensitive to dynamic multipath interference. Third and fourth generation receivers, in place since 2001, have made ATSC as resistant to multipath as DVB.

Aspect ratio

In order to view HDTV broadcasts, viewers may have to upgrade their TVs at some expense. Adding a new aspect ratio makes for consumer confusion if a display is capable of more than one ratio but must be switched to the correct one by the user. Traditional standard definition programs 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 the appearance of being too wide or not tall enough. Alternatively, viewers may choose to zoom the image which removes content that was on the top and bottom of the original TV show.[27]

Confusion about formats

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 for a period of time created confusion for consumers. This particular format war was "settled" with Blu-ray emerging as the victorious standard when Toshiba withdrew from the HD DVD format in February 2008, and then the HD DVD Promotion Group was dissolved on March 28, 2008.

Contemporary systems

Main article: Large-screen television technology
Components of a typical satellite HDTV system:
1. HDTV Monitor
2. HD satellite receiver
3. Standard satellite dish
4. HDMI cable, DVI-D and audio cables, or audio and component video cables

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 QAM tuner built-in and/or a card slot for inserting a CableCARD.[28]

High-definition image sources include terrestrial broadcast, direct broadcast satellite, digital cable, the high definition disc BD, internet downloads, the PlayStation 3, and the Xbox 360.

Recording and compression

Main article: High-definition pre-recorded media and compression

HDTV can be recorded to D-VHS (Digital-VHS or Data-VHS), W-VHS (analog only), to an 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 or more 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 who 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.[29] 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

Main characteristics of three HDTV 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) As defined in ETSI DVB TS 101 154 - as H.264 AVC and/or ISO/IEC 13818-2 (MPEG-2 – Layer II Audio) and/or 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 convolutional (I=12, M=17, J=1) 12 R-S block
Inner coding rate 2/3 Trellis code Punctured convolution 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, selectable time
Data randomization 16-bit PRBS
Modulation 8VSB (Only used for over the air transmission)
16VSB (Designed for cable, but rejected by the cable industry, cable TV uses 64QAM or 256QAM modulation as a de facto standard) 		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

TV resolution

See also

Wikimedia Commons has media related to High-definition television.

References

Cited references

  1. ^ "SBS jubilant with its 576p HD broadcasts".
  2. ^ "HDTV in the Russian Federation: problems and prospects of implementation (in Russian)".
  3. ^ "Researchers Craft HDTV's Successor".
  4. ^ "Digital TV Tech Notes, Issue #2".
  5. ^ James Sudalnik and Victoria Kuhl, "High definition television"
  6. ^ "High definition television comes of age thanks to ITU".
  7. ^ "History of the DVB Project".
  8. ^ "Digital TV Tech Notes, Issue #41".
  9. ^ The Grand Alliance includes AT&T, General Instrument, MIT, Philips, Sarnoff, Thomson, and Zenith)
  10. ^ Carlo Basile; et al. (1995). "The U.S. HDTV standard: the Grand Alliance". IEEE Spectrum. 32 (4): 36–45. {{cite journal}}: Explicit use of et al. in: |author= (help)
  11. ^ HDTV field testing wraps up
  12. ^ History of WRAL Digital
  13. ^ WRAL-HD begins broadcasting HDTV
  14. ^ Comark transmitter first in at Model Station
  15. ^ a b c Albiniak, Paige (1998-11-02). "HDTV: Launched and Counting". Broadcasting and cable. BNET. Retrieved 2008-10-24. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
  16. ^ "Space Shuttle Discovery: John Glenn Launch" (HTML). Internet Movie Database. 1998. Retrieved 2008-10-25. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)
  17. ^ "SES ASTRA and Euro1080 to pioneer HDTV in Europe" (Press release). SES ASTRA. October 23, 2003.
  18. ^ Bains, Geoff. "Take The High Road" What Video & Widescreen TV (April, 2004) 22-24
  19. ^ Howstuffworks "How HD-DVD Works"
  20. ^ "Draft HD DELIVERY FOR BBC WORLDWIDE, 2008-05-08" (PDF).
  21. ^ "1366x768 resolution problems on HDTV, HD-Ready, and High Definition TV".
  22. ^ "HDTV Channels". King of Sat. Retrieved November 23 2008. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |dateformat= ignored (help)
  23. ^ "T2 – THE NEXT GENERATION" (PDF) (Press release). DVB Project. June 30, 2008.
  24. ^ Julian Clover. "BBC begins DVB-T2 test transmissions" Broadband TV News (June 27, 2008)
  25. ^ "DirecTV HD Image Quality".
  26. ^ "DirecTV's HD future is MPEG-4".
  27. ^ HDTV display modes: Information and Much More from Answers.com
  28. ^ "HDTV information".
  29. ^ "5C Digital Transmission Content Protection White Paper" (pdf). 1998-07-14. {{cite web}}: Check date values in: |date= (help); Unknown parameter |lastaccess= ignored (help)

General references

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