High-definition video

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High-definition video or HD video refers to any video system of higher resolution than standard-definition (SD) video, and most commonly involves display resolutions of 1280×720 pixels (720p) or 1920×1080 pixels (1080i/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), the optical disc delivery system Blu-ray Disc and the video tape format D-VHS.


[edit] History

[edit] The developmental era (1948 - 1970s): low definition TV as high definition TV

From a historical perspective, NTSC or System-M was the first HD television transmission format.

System-M held the high definition video monopoly from 1948-1956. The only other existing TV broadcast systems in Europe at the time used either 405 lines (UK, also referred to as System-A) or 441 lines (France, but no system designator was ever issued).

When the Europeans standardized on using 625 lines with either PAL and SECAM as the colour standard. Essentially PAL became the globally available high definition video format. The French tried an 819 line system that was Monochrome only, but abandoned it due to interoperability issues and lack of adoption in other countries other than Belgium.

[edit] 1980s: Great technological leaps into dead ends

Original HD specifications date back to the early 1980s, when Japan developed the HighVision 1125-line TV standard (also called MUSE) that ran at 30 frames per second (frame/s or 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, but abandoned later on when it was replaced by a DVB analog standard. HighVision video is still usable for HDTV video interchange, but there is almost no equipment around to perform this function. All attempts at shoehorning in HighVision into a 6 MHz broadcast channel were mostly not successful. All attempts at using this format for terrestrial TV transmission were forsaken by the mid-1990s.

The Europeans developed HD-MAC (1250 lines, 50 Hz) as a video standard, but it never took off as a terrestrial video transmission format. HD-MAC was never designated for video interchange except by the European Broadcasting Union.

The current high definition video standards in North America were developed during the course of the advanced television process initiated by the Federal Communications Commission in 1987 at the request of American broadcasters. In essence the end of the 1980s was a death knell for most analog high definition technologies that had developed up to that time.

[edit] 1990s: DVB and the brushfire of standardization

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 1125/30 frame/s system) with a maximum frame rate of 30 frame/s, and 720 line video, progressively scanned, with a maximum frame rate of 60 frame/s.

In the end however the DVB standard of resolutions (1080, 720, 480...) and frame rates (24, 25, 30) were adopted in conjunction with the Europeans that were also involved in the same standardization process. 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.

[edit] 2000s: global HDTV adoption, but standardization deteriorates

In the early 2000s it looked as if DVD would be the video standard far into the future. However, both Brazil and China have adopted non-standard video codecs (mp4, and an open-source video codec) that somewhat violate the interoperability that was hoped for after decades of largely non-interoperable analog TV broadcasting. As high definition television has evolved into the mathematical representation of a video signal, and as computing power is so inexpensive these standardization issues so far have been minor.

[edit] Technical details

High definition video (prerecorded and broadcast) 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 Blu-ray Disc and the defunct HD DVD 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 draws the image field every other line or "odd numbered" lines during the first image refresh operation, and then draws the remaining "even numbered" 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 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; video engineers use the term 'picture' instead. 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 2.39:1 (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

Resolution (W×H) Pixels Aspect Ratio Video Format Description
1024×768 786,432 16:9 (non-square pixels) 720p/XGA Used on PDP HDTV displays with non square pixels
1280×720 -
1280×1080 1,382,400 16:9 (non-square pixels) 1080p Used on PDP HDTV displays (Full HD, HD Ready 1080p)
1920×1080 2,073,600 16:9 1080p—HDTV standard format Used on all types of HDTV technologies (Full HD, HD Ready 1080p)
3840×2160 8,294,400 16:9 2160p DCI Cinema 4k standard format Quad HDTV, (there is no HD Ready 2160p Quad HDTV format)

A common resolution used in HD Ready LCD TV panels is 1366 × 768[2] pixels instead of the ATSC Standard 1280 × 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, e.g. 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. Most HD-ready CRT TVs use 1080i resolution.

[edit] HD content

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

  • Most computers are capable of HD or higher resolutions over VGA, DVI, and/or HDMI.
  • The optical disc standard Blu-ray Disc can provide enough digital storage to store hours of HD video content. DVDs look best on screens that are smaller than 36 inches (91 cm), so they are not always up to the challenge of today's high-definition (HD) sets. Storing and playing HD movies requires a disc that holds more information, like a Blu-ray Disc.

[edit] Types of recorded medium

The high resolution photographic film used for cinema projection is exposed at the rate of 24 frames per second but usually projected at 48, each frame getting projected twice helping to minimise flicker. One exception to this was the 1986 National Film Board of Canada short film Momentum, which briefly experimented with both filming and projecting at 48 frame/s, in a process known as IMAX HD.

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, 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.

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.

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.

[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, Steven Soderbergh, 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:

[edit] Film to high-definition transfer

Most major motion pictures are shot on film. Film is a very high resolving medium, with resolution measured by testing its ability to resolve pairs of black and white lines, the unit of measurement is cycles/mm – one "cycle" consists of a pair of lines and is equivalent to two 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 reduced with each emulsion copying step and when the image passes through a lens (for example, on a projector). In many cases, 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] HD in video gaming

Video game systems, such as the PlayStation 3 and Xbox 360 can output an HD signal. The PlayStation Network and Xbox Live Marketplace services offer HD movies and video clips for download to their respective consoles.

The PlayStation 3 and Xbox 360 (seventh generation video consoles) can output display resolutions up to 1080p through both component and HDMI cables. While there are only a very limited number of games available which render the picture in 1080p, all games can be automatically upscaled to this resolution. Both Xbox 360 and PlayStation 3 games are labeled with their output resolution on the backs of their packaging. The Wii can output non-HD display resolutions up to 480p (NTSC).

[edit] See also

Look up HDTV in Wiktionary, the free dictionary.

[edit] References

[edit] Further reading

[edit] External links

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