High-Definition Television


The National Television Standards Committee (NTSC) developed the black-and-white TV broadcast system that was adopted by the FCC in 1942. The committee was convened again in 1950 to develop a color TV standard, which the FCC adopted in 1953 and which was compatible with broadcasts using the original black-and-white standard. NTSC is an analog transmission system that uses 525 scanning lines, broadcasting 30 complete frames per second. (The image is "interlaced": each frame is transmitted in two separate scans, 1/60th of a second apiece, each scan including every other line of the picture.) The picture is modulated using an amplitude modulated vestigial sideband scheme, and the sound is sent by FM technology. Picture and sound together occupy a channel of 6 MHz bandwidth.

The Advanced Television Systems Committee (ATSC) is a broadcasters/manufacturers industry association that documented the specifications for the Digital TV (DTV) system, which the FCC adopted in 1996. The standard has become known as the ATSC standard, just as the original U.S. standard is known as NTSC. ATSC worked with the FCC's official Advisory Committee on Advanced Television Service, which coordinated the selection criteria, system analysis, laboratory and field testing and allocation parameters that were proposed by the ATSC to the FCC.

The term Digital Television (DTV) applies to all the types of television broadcasting that use digital encoding and transmission, as opposed to analog transmission of NTSC broadcasts.

Standard Definition Television (SDTV) refers to digital TV broadcasts that provide about as much detail as ordinary analog broadcasts. SDTV pictures have 480 lines with 4:3 aspect ratio. Technologists expect that a digital TV channel will be able to carry, simultaneously, four or more SDTV programs, or some combination of HDTV, SDTV and other services.

High Definition Television (HDTV) brings wide-screen, high-resolution pictures and multichannel, compact-disc-quality sound to broadcast TV. The pictures attempt to equal 35mm film in image quality.

The ATSC system encompasses 18 different picture formats. 12 of these formats are for SDTV, and the remaining 6 are for HDTV, including 1920 x 1080 pixels (1080 lines) and 1280x720 pixels (720 lines). All six HDTV formats have 16:9 aspect ratios (ratio of width to height).

The following table lists all of the ATSC DTV formats:



Rates* (Hz)
480 640 Interlaced 4:3 30
480 640 Progressive 4:3 24, 30, 60
480 704 Interlaced 4:3 30
480 704 Progressive 4:3 24, 30, 60
480 704 Interlaced 16:9 30
480 704 Progressive 16:9 24, 30, 60
720 1280 Progressive 16:9 24, 30, 60
1080 1920 Interlaced 16:9 30
1080 1920 Progressive 16:9 24, 30
* For compatibility with NTSC, frame rates of 23.976, 29.97 and 59.94 Hz are also supported in cases where 24, 30 and 60 Hz are supported, respectively.

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