High-definition video

From Wikipedia, the free encyclopedia

High-definition (HD) video generally refers to any video system of higher resolution than standard-definition (SD) video, most commonly at display resolutions of 1280x720 (720p) or 1920x1080 (1080i or 1080p). This article discusses the general concepts of high-definition video, as opposed to its specific applications in television broadcast (HDTV), video recording formats (HDCAM, HDCAM-SR, DVCPRO-HD, D5-HD, XDCAM-HD, HDV and AVCHD), and optical disc delivery systems (Blu-ray and HD-DVD).

[edit] History

Original HD specifications date back to the early 1980s, when Japan developed an 1125-line TV standard operating at 30 frames per second (fps). Japan presented their standard at an international meeting of television engineers in Algiers in 1981 and Japan's NHK presented its analog HDTV system at Swiss conference in 1983. The NHK system was standardized in the United States as SMPTE (Society of Motion Picture and Television Engineers) standard #240M in the early 1990s.

Historically, the term high-definition television was used to refer to television standards developed in the late 1930s to replace the early experimental mechanically-scanned systems that ranged from 15 lines to about 220 lines of resolution. John Logie Baird of the UK was a major proponent of these early mechanically scanned systems, but they were quickly replaced by all-electronic systems developed by engineers such as Philo T. Farnsworth, Vladimir Zworykin and the EMI team including Alan Blumlein under Isaac Shoenberg.

The United Kingdom was the first to start regular broadcast television – the BBC Television Service – in 1936 from Alexandra Palace, initially with a 240-line, 25 frames-per-second (fps) mechanically-scanned system by Baird Television Limited alternating with a 405-line Marconi-EMI interlaced system at 50 fields per second (each frame consisting of two fields). The Baird system was dropped after the end of 1936. This was referred to as the world's first scheduled 'high definition' television service, and thus the term must be regarded as originally identifying systems offering 240-line resolution or better. The Marconi-EMI specification went on to be adopted across Europe as CCIR System A.

In the United States, the National Television System Committee (for which the NTSC standard is named) standardized on 525 lines at 30 fps in 1940, with regular broadcasts starting on July 1, 1941. The NTSC standard was updated to include first a non-compatible 441-line color standard in 1950, which was then replaced by a compatible 525-line, 29.97fps color standard approved in 1953 and used to this day. PAL (Phase Alternating Line) was developed in the late 1950s with 625 lines at 25 fps and went on the air in 1964. SECAM (SÉquentiel Couleur À Mémoire, French for "sequential colour with memory") was developed by France as the first European color television standard independent to the American NTSC standard, and soon competed by the West German PAL, also using 625 lines and 25 fps. SECAM was adopted during the Cold War by France and its colonial territories, as well as the Belgian colonies, and later adopted by countries rejecting the American standard, namely the Soviet Union, the Peoples' Republic of China, and their satellite communist governments.

The current high definition video standards were developed during the course of the advanced television process initiated by the Federal Communications Commission in 1987 at the request of American broadcasters. The FCC process, led by the Advanced Television Systems Committee (ATSC) adopted a range of standards from interlaced 1080 line video (a technical descendant of the original analog NHK 1125/30fps system) with a maximum frame rate of 30 fps, and 720 line video, progressively scanned, with a maximum frame rate of 60 fps. The FCC officially adopted the ATSC transmission standard (which included both HD and SD video standards) in 1996, with the first broadcasts on October 28, 1998.

The world has transmitted analog PAL, NTSC, SECAM for over 60 years. However, with the advent of digital broadcasting including HD formats, analog transmissions will cease in the coming years and NTSC, PAL and SECAM will pass into history, or so goes the most optimistic point-of-view. It remains to be seen if and when this can be achieved, due to the vast amounts of analog video equipment (TV stations and home TVs) which are currently installed.

[edit] Details

High definition video (prerecorded and broadcasted) is defined threefold, by:

• The number of lines in the vertical display resolution. High-definition television (HDTV) resolution is 1080 or 720 lines. In contrast, regular digital television (DTV) is 480 lines (upon which NTSC is based, 480 visible scanlines out of 525) or 576 lines (upon which PAL/SECAM are based, 576 visible scanlines out of 625). However, since HD is broadcast digitally, its introduction sometimes coincides with the introduction of DTV. Additionally, current DVD quality is not high-definition, although the high-definition disc systems HD DVD and Blu-ray Disc are.

• 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.^[1] 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. High-definition signals require a high-definition television or computer monitor in order to be viewed. High-definition video has an aspect ratio of 16:9 (1.78:1). The aspect ratio of regular widescreen film shot today is typically 1.85:1 or 2.40:1 (sometimes traditionally quoted at 2.35:1). Standard-definition television (SDTV) has a 4:3 (1.33:1) aspect ratio, although in recent years many broadcasters have transmitted programs "squeezed" horizontally in 16:9 anamorphic format, in hopes that the viewer has a 16:9 set which stretches the image out to normal-looking proportions, or a set which "squishes" the image vertically to present a "letterbox" view of the image, again with correct proportions.

[edit] High-Definition Display Resolutions

A common resolution used in HD Ready LCD TV panels is 1366 x 768^[2] 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.

[edit] Sources

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.

• 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.^[3]

[edit] Types of prerecorded 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. Template: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.

See also: Deinterlacing

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. This is also the medium for High Definition Broadcasts around the world and 1080p is used for Blu-Ray movies and HD-DVD.

[edit] HD in filmmaking

Film as a medium has inherent limitations, such as difficulty of viewing footage whilst recording, and suffers other problems, caused by poor film development/processing, or poor monitoring systems. Given that there is increasing use of computer-generated or computer-altered imagery in movies, and that editing picture sequences is often done digitally, some directors have shot their movies using the HD format via high-end digital video cameras. Whilst the quality of HD video is very high compared to SD video, and offers improved signal/noise ratios against comparable sensitivity film, film remains able to resolve more image detail than current HD video formats. In addition some film has a wider dynamic range (ability to resolve extremes of dark and light areas in a scene) than even the best HD cameras. Thus the most persuasive arguments for the use of HD are currently cost savings on film stock and the ease of transfer to editing systems for special effects. Notable directors who have used HD to a large degree thus far are: George Lucas, Michael Mann, and Robert Rodriguez.

Many television shows with science fiction themes and special effects such as Star Trek: Enterprise, Stargate SG-1, Stargate Atlantis and the re-imagined Battlestar Galactica have also begun to use digital cameras.

Movies that have been shot on HD digital video include:

• Crank
• One Six Right: The Romance of Flying
• The Quiet
• Apocalypto
• Star Wars Episode II: Attack of the Clones
• Star Wars Episode III: Revenge of the Sith
• You Move You Die
• Spy Kids 2: The Island of Lost Dreams
• Spy Kids 3-D: Game Over
• Once Upon a Time in Mexico
• Sin City
• Sky Captain and the World of Tomorrow
• Russian Ark
• Scary Movie 4
• Collateral
• Miami Vice
• Superman Returns
• Voyeur Beach
• Find Me Guilty
• Wolf Creek
• Silent Hill (Darkness scenes)
• Dogville
• Flyboys
• Rocky Balboa (Boxing match scenes)
• My Name is Bruce
• My Scary Girl
• Bubble
• The Waiter (film)(2006)
• The Pink Panther
• Planet Terror

[edit] Film to high-definition transfer

Most major motion pictures are shot in negative film. Film negative is a very high resolving medium, with resolution measured in cycles/mm. One cycle is also called one line pair which consists of one black line and one white line. In simple terms, one cycle is equivalent to 2 pixels, one black and one white. Film by itself can commonly resolve from 50 c/mm to 400 c/mm (100 pixels/mm to 800 pixels/mm) depending on emulsion stock. However, since the image on film is formed by exposing it through a lens and this lens also has its own resolution limits, the final resolution on the photographed negative is always less than each component's individual resolution.

Depending on the year and format a movie was filmed in, the exposed image can vary greatly in size. Sizes range from as big as 24 mm × 36 mm for VistaVision/Technirama 8 perforation cameras (same as 35 mm still photo film) going down through 18 mm × 24 mm for Silent Films or Full Frame 4 perforations cameras to as small as 9 mm × 21 mm in Academy Sound Aperture cameras modified for the Techniscope 2 perforation format. Movies are also produced using other film gauges, including 70 mm films (22 mm × 48 mm) or the rarely used 55 mm and CINERAMA.

The four major film formats provide pixel resolutions (calculated from pixels per millimeter) roughly as follows:

• Academy Sound (Sound movies before 1955): 15 mm × 21 mm (1.375) = 2160 × 2970
• Academy camera US Widescreen: 11 mm × 21 mm (1.85) = 1605 × 2970
• Current Anamorphic Panavision ("Scope"): 17.5 mm × 21 mm (2.39) = 2485 × 2970
• Super-35 for Anamorphic prints: 10 mm × 24 mm (2.39) = 1420 × 3390

In the process of making prints for exhibition, this negative is copied onto other film (negative → interpositive → internegative → print) causing the resolution to be decimated with each emulsion copying step and when the image passes through a lens (for example, on a projector). In many case, the resolution can be reduced down to 1/6th of the original negative's resolution (or worse). Note that resolution values for 70 mm film are higher than those listed above.

Typical high-definition home video uses the following resolutions:

• 1280 × 720
• 1920 × 1080

Usually when studios master movies for home video release they use assets in high resolution and then master them to 1920 × 1080 and/or 1280 × 720. For standard definition applications (e.g., DVD or SDTV), they are also anamorphically compressed and mastered to 720 × 576 (PAL) and 720 × 480 (NTSC).

[edit] See also

• 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
• mariposaHD
• Ultra High Definition Video

[edit] References

• United States Federal Standard 1037C
• DTV channel protection ratios
• DVB HDTV standard
• Images formats for HDTVPDF (549 KiB), article from the EBU Technical Review .
• High Definition for Europe - a progressive approachPDF (207 KiB), article from the EBU Technical Review .
• High Definition (HD) Image Formats for Television ProductionPDF (117 KiB), technical report from the EBU
• Digital Terrestrial HDTV Broadcasting in EuropePDF, technical report from the EBU
• TV Azteca Plans HDTV Mexican Rollout

[edit] External links

• ATSC
• CDTV Canadian Digital Television official website
• Home Theater Network What to look for in HDTVs.
• mariposaHD The world's first original HDTV show made for the Internet. Free 1080i and 720p videos, in WMV HD format, distributed with BitTorrent.

es:Alta definición ko:고선명 비디오 ms:Video definisi tinggi ja:高精細度ビデオ sk:Video s vysokým rozlíšením (všeobecne)