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.
