Digital TV in the U.S.
Altogether 18 picture formats with varying resolutions appear in the specifications of the Advanced Television Systems Committee (ATSC) but only four concern home viewers today. These comprise two high-definition (HD) and two standard-definition (SD) television displays, where the picture is either progressively scanned or interlaced. Eventually, another HD format will emerge (the so-called "1080p").
In the resolution column of the table, the first figure gives the number of horizontal picture-elements (pixels) per TV line, and the second the number of TV scanning lines. The figure in parentheses indicates total pixels transmitted per frame. Bit-rate indicates the millions of bits per second needed for a picture comprising 60, 30, or 24 frames per second—before compression is applied to transmit it.
In today's United States, the analog National Television Standards Committee (NTSC) system transmits 30 frames per second as 60 interlaced, alternating fields. HDTV 1080i does the same, though with greater vertical resolution (1080 vs. 540 lines). But HDTV 720p and the SDTV formats transmit 30 frames progressively, drawing the entire frame in a single scan. It's envisioned that DTV formats will some day carry double the amount of vertical information, providing 60 frames per second progressively scanned. The 24-frame rate applies to programming originally produced on movie film, with its inherently higher resolution, as opposed to video- or PC-generated material.