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NTSC

From Chace Audio, Wikipedia

The National Television System Committee (NTSC) is the analog television system developed by the United States. By the late 20th century, the NTSC standard was in use by most of North America, Central America, northern and western South America, and some of southeast Asia.

NTSC is also the name of the U.S. standardization body (formed in 1940 by the Federal Communications Commission or FCC) that adopted the standard. It was first developed prior to the Second World War and had no provision for color transmissions. In 1953, an updated standard was issued that allowed for color broadcasting to be compatible with existing black-and-white receivers and also maintained the broadcast channel bandwidth already in use.

Color information was added to the black-and-white image by adding a color sub-carrier of approximately 3.58MHz to the video signal. In order to minimize interference between the chrominance signal and FM sound carrier, the addition of the color sub-carrier also required a slight reduction of the frame rate from 30 to 29.97 frames per second.

NTSC utilizes 525 scan lines and 30 frames per second consisting of two interlaced fields per frame for a total of 262.5 lines per field or 60 fields per second - the same rate as the 60Hz alternating current power in the US. The aspect ratio of 4:3 was standard, as was frequency modulation (FM) for the sound signal. Of each frame's 525 scan lines, 486 make up the visible raster. The remaining lines (the vertical blanking interval) are used for synchronization and vertical retrace and can contain other data such as closed captioning and vertical interval time code. The even numbered or “lower” lines (21-263) are drawn in the first field, and the odd-numbered or “upper” lines (283 -525) are drawn in the second field to yield a flicker-free image at a field refresh frequency of approximately 59.94Hz. By comparison, PAL uses 625 scan lines (576 visible) and so has a higher vertical resolution but a lower temporal resolution of 25 frames - just 50 fields per second.

NTSC has been jokingly referred to as standing for “Never Twice the Same Color” due to phase issues with its color signal. The European PAL and SECAM analog color broadcast standards came later than NTSC's color standard, and those committees addressed the color phase issue as they were developed.

After over a half-century of use, over-the-air NTSC transmission will be replaced with ATSC in the United States in 2009.

This article is licensed under the GNU Free Documentation License found at http://www.gnu.org/copyleft/fdl.html. It uses material from the Wikipedia article at http://en.wikipedia.org/wiki/Ntsc.

A map of NTSC, SECAM, and PAL standards in the 20th Century. 21st Century standards will change in 2009 to adopt digital broadcasts.

pal-ntsc-secam12.svg.png