High-definition video
High-definition video is video of higher resolution and quality than standard-definition. While there is no standardized meaning for high-definition, generally any video image with considerably more than 480 vertical scan lines or 576 vertical lines is considered high-definition. 480 scan lines is generally the minimum even though the majority of systems greatly exceed that. Images of standard resolution captured at high frame rate, by a high-speed camera may be considered high-definition in some contexts. Some television series shot on high-definition video are made to look as if they have been shot on film, a technique which is often known as filmizing.
History
The first electronic scanning format, 405 lines, was the first high definition television system, since the mechanical systems it replaced had far fewer. From 1939, Europe and the US tried 605 and 441 lines until, in 1941, the FCC mandated 525 for the US. In wartime France, René Barthélemy tested higher resolutions, up to 1,042. In late 1949, official French transmissions finally began with 819. In 1984, however, this standard was abandoned for 625-line color on the TF1 network.Analog
Modern HD specifications date to the early 1980s, when Japanese engineers developed the HighVision 1,125-line interlaced TV standard that ran at 60 frames per second. The Sony HDVS system was presented at an international meeting of television engineers in Algiers, April 1981 and Japan's NHK presented its analog high-definition television system at a Swiss conference in 1983.The NHK system was standardized in the United States as 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 modern equipment available to perform this function. Attempts at implementing HighVision as a 6 MHz broadcast channel were mostly unsuccessful. All attempts at using this format for terrestrial TV transmission were abandoned by the mid-1990s.
Europe developed HD-MAC, a member of the MAC family of hybrid analogue/digital video standards; however, it never took off as a terrestrial video transmission format. HD-MAC was never designated for video interchange except by the European Broadcasting Union.
Digital
High-definition digital video was not possible with uncompressed video due to impractically high memory and bandwidth requirements, with a bit rate exceeding for 1080p video. Digital HDTV was enabled by the development of discrete cosine transform video compression. The DCT is a lossy compression technique that was first proposed by Nasir Ahmed in 1972, and was later adapted into a motion-compensated DCT algorithm for video coding formats such as the H.26x formats from the Video Coding Experts Group from 1988 onwards and the MPEG formats from 1993 onwards. Motion-compensated DCT compression significantly reduced the amount of memory and bandwidth required for digital video, capable of achieving a data compression ratio of around 100:1 compared to uncompressed video. By the early 1990s, DCT video compression had been widely adopted as the video coding standard for HDTV.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.
The FCC process, led by the Advanced Television Systems Committee adopted a range of standards from interlaced 1,080-line video with a maximum frame rate of 30 Hz, and 720-line video, progressively scanned, with a maximum frame rate of 60 Hz.
In the end, however, the DVB standard of resolutions and respective frame rates were adopted in conjunction with the Europeans that were also involved in the same standardization process. The FCC officially adopted the ATSC transmission standard in 1996.
In the early 2000s, it looked as if DVB would be the video standard far into the future. However, both Brazil and China have adopted alternative standards for high-definition video that preclude the interoperability that was hoped for after decades of largely non-interoperable analog TV broadcasting.
Technical details
High definition video is defined threefold, by:- The number of lines in the vertical display resolution. High-definition television resolution is 1,080 or 720 lines. In contrast, regular digital television is 480 lines or 576 lines. 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 HD DVD are.
- The scanning system: progressive scanning or interlaced scanning . Progressive scanning redraws an image frame when refreshing each image, for example 720p/1080p. 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, for example 1080i. Interlaced scanning yields 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. In Europe more common television broadcasting system and in USA . The 720p60 format is 1,280 × 720 pixels, progressive encoding with 60 frames per second. The 1080i50/1080i60 format is 1920 × 1080 pixels, interlaced encoding with 50/60 fields, per second. Two interlaced fields formulate a single frame, because the 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.
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 progressive 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. The aspect ratio of regular widescreen film shot today is typically 1.85:1 or 2.39:1. Standard-definition television has a 4:3 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.
The EU defines HD resolution as 1920 x 1080 pixels or 2 073 600 pixels and UHD resolution as 3840 x 2160 pixels or 8 294 400 pixels.
Common high-definition video modes
Ultra high-definition video modes
Note: 1 Image is either a frame or, in case of interlaced scanning, two fields.Also, there are less common but still popular UltraWide resolutions, such as p.
There is also a WQHD+ option for some of these.
HD content
High-definition image sources include terrestrial broadcast, direct broadcast satellite, digital cable, high definition disc, digital cameras, Internet downloads, and video game consoles.- Most computers are capable of HD or higher resolutions over VGA, DVI, HDMI and/or DisplayPort.
- The optical disc standard Blu-ray Disc can provide enough digital storage to store hours of HD video content. Digital Versatile Discs or DVDs, are not always up to the challenge of today's high-definition sets. Storing and playing HD movies requires a disc that holds more information, like a Blu-ray Disc or the now-defunct High Definition Digital Versatile Discs which held 15 GB or 30 GB in, respectively, single and double layer variations.
Types of recorded media
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, 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 percent. 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, and the next is held for two video fields and then the process is repeated, thus achieving the correct film projection rate with two film frames shown in one twelfth of a second.
Older 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, 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. 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.