How is HDTV different?

The usual National Television Standards Committee (NTSC) analog TV screen in the U.S. has 525 scan lines, with 480 actually visible.

The usual TV has an effective picture resolution of about 210,000 pixels. In the highest resolution digital TV formats, each picture contains about 2 million pixels. This means about 10 times more picture detail on the HDTV screen!

DTV may be in either 4:3 or 16:9 format.

The typical TV show uses 35-mm film (or is recorded direct-to-video using NTSC equipment). In the case of film, the broadcaster converts it to an analog TV signal for broadcasting. Standard 35-mm film has an aspect ratio of 1.37:1, meaning it is 1.37 times as wide is it high. A conventional TV screen has a 4:3 (1.33:1) aspect ratio, so the conversion is easy.

To deal with HDTV's new standards, broadcasters will need to get all new equipment, such as cameras, remote broadcast units, control rooms, cables, and sound equipment. This is because digital TV has:

• Wider images
• Much more detailed pictures
• 5.1 channel CD-quality Dolby Digital (AC-3) surround sound
• The ability to send data directly to a screen or to a PC as a download (The actual HDTV transmission is based on a 19.3-Mbps digital data stream.)

The aspect ratio (width to height) of digital TV is 16:9 (1.78:1), which is closer to the ratios used in theatrical movies, typically 1.85:1 or 2.35:1. Currently broadcasters must either pan and scan the image (crop the full picture of the film down to 4:3, eliminating part of every scene in the process) or letterbox it (present the full picture only on the middle part of the screen, with black bars above and below it). With a 16:9 screen, panning and scanning a theatrical movie doesn't remove so much from the original picture and letterboxing doesn't block out so much of your screen.