NTSC
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NATIONAL TELEVISION STANDARDS COMMITTEE
NTSC or the National Television System(s) Committee was an industry-wide standardization body created in 1940 by the Federal Communications Commission (FCC) in order to resolve conflicts which existed at the time between companies regarding the introduction of a nation-wide analog television system for the United States. It has issued a black-and-white standard in March 1941. In January 1950 the committee was re-created, this time to decide about color television, and in March 1953 unanimously approved what is now simply called the NTSC color television standard. The update retained full compatibility with older black-and-white television sets.
Digital Television (DTV) is scheduled to replace all existing terrestrial analog NTSC television transmissions in the U.S. by the year 2006. This doesn't necessarily affect home video formats, direct satellite transmission or cable television but the range of services and potential improvement in image quality will probably drive those industries as well. Several simul-taneous Standard Definition Television (SDTV) image streams or a single High Definition Television (HDTV) image will make up the television programming broadcasts. SDTV is considered roughly the same quality level as today's television broadcasts and HDTV relates to a number of higher definition video standards. In any case, a television image in SDTV or HDTV will be transmitted in 16:9 aspect ratio. Both of these broad television formats are considered to be Advanced Television or short ATV.
The current NTSC broadcasts are in 4:3 aspect ratio. This means that no matter what the screen size is, the image will measure 4 units wide and 3 units tall. The primary feature of the ATV formats is a 16:9 picture aspect ratio, which comes out to be about 20% wider than a 4:3 image of equal height. Independent of the aspect ratio is the number of scan lines available on the screen and the number of pixels available across the width of the screen. The higher the line and pixel count, the better the potential resolution of the image.
SOURCES:
http://en.wikipedia.org/wiki/NTSC
http://www.henninger.com/library/hdtvfilm/