720p is the shorthand name for a category of HDTV video modes. High-definition television (HDTV is a Digital television Broadcasting system with higher resolution than traditional television systems (standard-definition The number 720 stands for 720 lines of vertical display resolution, while the letter p stands for progressive scan or non-interlaced. The display resolution of a Digital television or Computer display typically refers to the number of distinct pixels in each dimension that can be displayed Progressive or noninterlaced scanning is a method for displaying storing or transmitting Moving images in which all the lines of each frame are drawn in For the method of incrementally displaying Raster graphics, see Interlace (bitmaps. When broadcast at 60 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 spatial (sharpness) resolution is much closer to 1080i than the number of scan lines would suggest.

Contents 1 Specifications 2 Compatibility 3 History 4 720p versus 1080i 5 See also 6 References 7 External links

Specifications

720p assumes a widescreen aspect ratio of 16:9, a vertical resolution of 720 pixels and a horizontal resolution of 1280 pixels for a total of about 0. A widescreen image is a film computer or television image with a wider and shorter aspect ratio than the standard Academy frame developed during the Classical The aspect ratio of an Image is its width divided by its height 92 million pixels. In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image The frame rate (in this case equal to the field rate) can be either implied by the context or specified in hertz after the letter p. Frame rate, or frame frequency, is the measurement of the Frequency (rate at which an imaging device produces unique consecutive images called frames The The field rate of an Interlaced video image is twice the effective Frame rate, since interlacing draws only half of the image (the odd- or even-numbered lines at The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. The five 720p frame rates in common use are 24, 25, 30, 50 and 60 Hz (or frame/s). Frame rate, or frame frequency, is the measurement of the Frequency (rate at which an imaging device produces unique consecutive images called frames The 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 or field rates, whereas traditional NTSC countries (North and Central America, Japan, South Korea, Philippines) are using 24p (for movies), and 60p for high motion programming. PAL, short for Phase Alternating Line, is a colour -encoding system used in Broadcast television systems in large parts of the world SECAM, also written SÉCAM ( Séquentiel couleur à mémoire, French for "Sequential Color with Memory" is an analog color television system NTSC ( National Television System Committee) is the Analog television system used in the United States, Canada, Japan, Mexico High motion is the characteristic of video or film footage displayed possessing a sufficiently high frame rate (or field rate that moving images do not blur or strobe even when tracked All variants can be transported by both major digital television formats, ATSC and DVB. Digital television (DTV is the sending and receiving of moving images and sound by discrete ( digital) signals in contrast to the analog signals used by For the chemical compound see Divinylbenzene. Digital Video Broadcasting ( DVB) is a suite of internationally accepted

Compatibility

720p is directly compatible with newer flat-panel technology such as plasma and LCD, which are inherently progressive and must perform deinterlacing to display 1080i source material. A plasma display panel (PDP is a type of Flat panel display now commonly used for large TV displays (typically above 37-inch or 940 mm Deinterlacing is the process of converting Interlaced video like common Analog television signals into a non-interlaced form 720p must be scan-converted for display on most CRT-based consumer televisions, which are generally interlaced-only display devices. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or ^[1] However, CRTs intended for use as computer monitors are progressive-only devices that are generally able to support 1280×720 at 60 Hz.

History

720p was designed at AT&T Bell Laboratories in the late 1980s, under the supervision of Arun Netravali. Arun N Netravali (born May 26, 1946 in Bombay) is an Indian-American Engineer who is a pioneer of digital technology including The project began when Zenith approached AT&T to partner in the design of an analog HDTV format, comparable to the Japanese system. Netravali (in Murray Hill), along with Barry Haskell (in Holmdel) and other image processing experts at Bell Labs, and William Schreiber at MIT, quickly devised a digital standard using DCT block coding. About 50 engineers were hired and a prototype was assembed in Murray Hill using Xilinx programmable logic hardware. Xilinx Inc ( is the world's largest developer and fabless manufacturer of a class of reconfigurable hardware chips known as Field-programmable gate arrays The leaders of Zenith and AT&T cancelled 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.

720p versus 1080i

Some broadcasters use 720p50/60 as their primary high-definition format; others use the 1080i standard. While 720p presents a complete 720-line frame to the viewer between 24 and 60 times each second (depending on the format), 1080i presents the picture as 50 or 60 partial 540-line "fields" per second (24 complete 1080-line fields, or "24p" is included in the ATSC standard though) which the human eye or a deinterlacer built into the display device must visually and temporally combine to build a 1080-line picture - in Chase Herrmann type display. To get all 1080 interlaced lines to appear on the screen at the same time on a progressive high-definition display, the processor within the HD set has to weave together both 540-line segments to form the full-resolution frame. It does so by holding the first field in its memory, receiving the next field, then electronically knitting the two fields together. The combined fields are displayed at once as a complete 1080p frame. The main tradeoff between the two is that 1080i shows more detail than 720p for a stationary shot of a subject, at the expense of a lower effective refresh rate and the introduction of interlace artifacts during motion. For the method of incrementally displaying Raster graphics, see Interlace (bitmaps.

While 1080i has more scan lines than 720p, they do not translate directly into greater vertical resolution. Interlaced video is usually blurred vertically (filtered) to prevent twitter. Twitter is a flickering of fine horizontal lines in a scene, lines that are so fine that they only occur on a single scan line. Because only half the scan lines are drawn per field, fine horizontal lines may be missing entirely from one of the fields, causing them to flicker. Images are blurred vertically to ensure that no detail is only one scan line in height. Therefore, 1080i material does not deliver 1080 scan lines of vertical resolution. However 1080i provides a 1920-pixel horizontal resolution, greater than 720p's 1280 resolution.

In the USA, 720p is used by ABC, Fox Broadcasting Company and ESPN because the smoother image is desirable for fast-action sports telecasts, whereas 1080i is used by CBS, NBC, HBO, Showtime and Discovery HD due to the crisper picture particularly in non-moving shots. The United States of America —commonly referred to as the The American Broadcasting Company ( ABC) is an American Television network. ESPN, originally an acronym for Entertainment and Sports Programming Network, is an American Cable television network dedicated to CBS Broadcasting Inc ( CBS) is an American radio and Television network. The National Broadcasting Company ( NBC) is an American Television network headquartered in the GE Building in New York City's Showtime is a subscription television Brand used by a number of channels and platforms around the world but primarily refers to a group of channels in the United Discovery HD is the international name of the high-definition Television channels from Discovery Communications.

The European Broadcasting Union (EBU) recommends that its members use 720p50 with the possibility of 1080i50 on a programme-by-programme basis and 1080p50 as a future option. The European Broadcasting Union ( EBU; L'Union Européenne de Radio-Télévision ("UER" and unrelated to the European Union) is a confederation ^[2][3][4] The BBC is one of the EBU members transmitting in HDTV. It has not yet made a final decision on picture scanning format. Sveriges television in Sweden, Cyfra+ in Poland, SRG SSR idée suisse in Switzerland and ORF in Austria broadcast in 720p50. Sveriges Television AB ( SVT,) is a national Television broadcaster based in Sweden, funded by an obligatory fee payable by all Television -owners Cyfra+ is a Polish digital satellite platform owned and operated by French media company Canal+ ("Cyfra" is Polish for "Digit" SRG SSR idée suisse is the Swiss Public broadcasting organisation founded in 1931. All other commercial European HDTV services so far use 1080i50.

See also

• 1080p, 720i, 576p, 480p
• High-definition television (HDTV)
• 720re

References

External links

• HD standards in use.

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