720p
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720p is the shorthand name for a category of HDTV video modes. The number 720 stands for the 720 horizontal scan lines of display resolution (also known as 720 pixels of vertical resolution), while the letter p stands for progressive scan or non-interlaced. When broadcast at 60[1] frames per second, 720p features the highest temporal (motion) resolution possible under the ATSC and DVB standards. Progressive scanning reduces the need to prevent flicker by filtering out fine details, so sharpness is much closer to 1080i than the number of scan lines would suggest.[2][3]
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Specifications
720p has a widescreen aspect ratio of 16:9, a vertical resolution of 720 pixels and a horizontal resolution of 1280 pixels, that is 1280×720, for a total of 921,600 pixels. The 1280×720 format is always progressive scan, there is no interlace version of 1280×720. For legacy material it can also be used with an aspect ratio of 4:3 and then is 960×720 px.
The 1280×720 frame rates in common use are 23.976, 24, 25, 30, 50, 59.94 and 60 Hz. In general, traditional PAL and SECAM countries (Europe, Australia, much of Asia, Africa, and parts of South America) are or will be using the 25p and 50p frame rates, whereas traditional NTSC countries (North and Central America, Japan, South Korea, Philippines) are shooting 24p (movies), and 59.94p for high motion programming. All variants can be transported by both major digital television formats, ATSC and DVB.
Newer displays have a native resolution higher than a native 1280×720 resolution, often 1366×768, since this reduces manufacturing costs[why?]. However the only 720p format actually transmitted in the US is 1280×720/59.94p.
Compatibility
720p is directly compatible with newer flat-panel technology such as plasma and LCD, LCD projector, and progressive-scan CRTs. 720p must be scan-converted for display on interlace-only displays such as CRTs, but these have almost completely vanished from retail stores today, especially in developed countries(in other parts of world, CRT still holds a major market share).
Displays with exactly 1280x720 native resolution have become more common as the HDTV market matures, and variants based on XGA such as 1280x768 and 1366x768 are becoming less common. (Such monitors do not usually display 720p content well.) For the difference between 720p and 1080p to be noticeable, a viewer must be closer than about one screen width from the screen. As a result, TV sets smaller than 30 inches diagonal rarely support resolutions beyond 720p. Monitors intended for use as computer displays will have higher resolutions, often no tuner, and resolutions that are not exactly 16:9. 1440p (exactly double 720p) appears to be an emerging standard in computer monitors.
History
720p was designed at AT&T Bell Laboratories in the late 1980s, under the supervision of Arun Netravali. The project began when Zenith approached AT&T to partner in the design of an analog HDTV format, comparable to the Japanese system. Netravali (Bell Labs in Murray Hill, New Jersey), along with Barry Haskell (Bell Labs in Holmdel, New Jersey) and other image processing experts at Bell Labs, and William F. Schreiber[4][5] at MIT, quickly devised a digital standard using DCT block coding. About 50 engineers were hired and a prototype was assembled in Murray Hill using Xilinx programmable logic hardware. The leaders of Zenith and AT&T canceled the analog-HDTV project after the completion of the digital 720p experimental system, and Zenith agreed to design a radio-frequency modem system for broadcasting digital video. The 720p system was tested against competing standards during FCC trials, and was particularly notable for its lack of flicker and shimmer of moving edges.[citation needed] The conflict between interlaced formats (supported by the television industry) and progressive scan formats (supported by AT&T, Microsoft and others) was extremely contentious in the early days of format proposals.
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See also
References
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This article may require cleanup to meet Wikipedia's quality standards. Please improve this article if you can. (August 2009) |
- ^ Note: It is often actually broadcast at 60/1.001 FPS, which is approximately 59.94. http://www.tvtechnology.com/article/60026
- ^ afterdawn.com - 720p
- ^ CNET - Glossary - 720p
- ^ William F. Schreiber, PhD. Archival web site containing personal and professional data and collected writings
- ^ "William F. Schreiber Oral History", 9 January 2009, IEEE
External links
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