On April 4, 1997, the FCC ushered in digital television (DTV) by giving 6MHz of spectrum to approximately 1,500 stations for DTV broadcasting. The decree required the three commercial networks in the top ten markets to broadcast digitally by May 1, 1999, with markets 11 through 30 online by November 1, 1999. All stations must broadcast digitally by 2006, when their current analog spectrum is scheduled to revert back to the Fed.
While there is only one standard, there are 18 different video formats. The first split is between high definition and standard definition TV. Six of the video formats in the ATSC DTV standard are high definition TV: these are the 1080-line by 1920-pixel formats at 24 and 30 frames per second (1080i) , and at 60 fields per second for interlaced HDTV, and the 720-line by 1280-pixel formats at 24, 30 and 60 fps (720p). The HDTV formats have a 16:9 aspect ratio.
The 12 video formats which compose the remainder are standard definition television — not high definition. These consist of the 480-line by 704-pixel formats in 16:9 widescreen and 4:3 aspect ratios (at the 24, 30 and 60 pictures per second rates); and the 480-line by 640-pixel format at a 4:3 aspect ratio at the same picture rates.
The formats which represent HDTV are 1020i and 720p. The “i” and the “p” in the format names refer to interlaced and progressive scanning. In interlaced scanning, half of the lines in a full frame are scanned onto the screen in a sixtieth of a second, followed by the remaining half of the scan lines in the next sixtieth. The odd lines are scanned first, then filled in by the even lines.
In an attempt to meet expectations, many plasma manufacturers are building both standards into their units.