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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 standard. 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, or 1280x720, for a total of 921,600 pixels. The 1280x720 format is always progressive scan, there is no interlace version of 1280x720. The 1280x720 frame rate in common use are 23.976, 25, 30, 50 and 59.94p frame/s. 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 23.976 (for 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 720p, but have a native resolution higher or lower than a native 1280×720 resolution. This is because it helps cut manufacturing costs. However the only 1280x720 format actually transmitted by US based broadcast and satellite networks is 1280x720/59.94p.

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.

Actual 1280x720 flat-panel native resolution is uncommon. Displays with 1280x720 resolution include the Gateway FPD1775W, Westinghouse LCM-27w4, HP w15v, a small number of notebooks, and some Toshiba and Sharp televisions. Most TV's capable of 720p but not 1080p are 1280x768, 1280x800, 1360x768, 1366x768, 1440x900, or 1680x1050 resolution and display 720p with letterboxing or scaling. For resolutions with 1280 horizontal resolution, but higher than 720 vertical resolution, 1280x720 can be displayed with letterboxing. For higher resolution displays, displaying 720p without scaling requires windowboxing, available if the display supports 1:1 pixel mapping.

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. 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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