(Digital TeleVision) Transmitting TV using digital signals. The major DTV standards are ATSC (North America), DVB (Europe) and ISDB (Japan). All three use MPEG-2 video compression and Dolby Digital audio compression. DVB and ISDB also include MPEG audio compression.
In the U.S., the FCC approved the ATSC standard in late 1996 (see ACATS). In 1998, DTV debuted in major U.S. cities, and the FCC mandated that broadcasters switch to digital by 2006 and turn off analog transmission. In 2005, the deadline was extended to February 17, 2009, and then to June 12, 2009 at the last minute (see digital TV transition). Other countries have adopted the ATSC format, including Canada, South Korea, Taiwan and Argentina.
A Digital TV or a Set-Top Box
To receive a DTV program requires a digital TV set or a digital set-top box for an analog TV. However, digital TV sets may continue to have analog inputs for many years, because people have huge collections of VHS movies and recordings.
Eighteen DTV Formats
DTV offers 18 digital formats starting with Standard Definition (SD), the digital counterpart of the NTSC analog standard, except without snow and ghosts. Enhanced Definition (ED) offers the most formats (see table below). High Definition (HD) provides 5.1 Dolby Digital Surround Sound and requires a wide screen TV set (16:9) in order to eliminate the letterbox effect. Increasingly, programs are being transmitted in HDTV.
As you can see from the table below, the numerous options provide the broadcaster with a tradeoff between how many channels can be sent versus channel quality. The more HD channels, the fewer ED and SD channels, and vice versa. See digital TV transition, TV converter box, HDTV, letterbox, NTSC, 8-VSB, interlace, digital cable and cliff effect.
p = progressive scan (non-interlaced)
i = interlaced
Frame
Resolution Aspect Rate Pixel
Horiz x Vert Ratio (fps) Shape
HD - High Definition TV (HDTV)
1. 1920 x 1080 16:9 24p Square
2. 1920 x 1080 16:9 30p Square
3. 1920 x 1080 16:9 30i** Square
4. 1280 x 720 16:9 24p Square
5. 1280 x 720 16:9 30p Square
6. 1280 x 720 16:9 60p** Square
ED - Enhanced Definition TV (EDTV) - 480p
7. 704 x 480 16:9 24p Rectangle
8. 704 x 480 16:9 30p Rectangle
9. 704 x 480 16:9 60p** Rectangle
10. 704 x 480 4:3 24p Rectangle
11. 704 x 480 4:3 30p Rectangle
12. 704 x 480 4:3 60p** Rectangle
13. 640 x 480 4:3 24p Square
14. 640 x 480 4:3 30p Square
15. 640 x 480 4:3 60p Square
SD - Standard Definition TV (SDTV) - 480i
16. 704 x 480 16:9 30i Rectangle
17. 704 x 480 4:3 30i** Rectangle
18. 640 x 480 4:3 30i Square
** most popular formats
RELATED FORMATS:
DVD - DV/MiniDV
720 x 480 x 30 fps (NTSC)
720 x 576 x 25 fps (PAL/SECAM)
Only 704 of the 720
horizontal pixels are visible.
D1 Broadcast Format
720 x 486 x 30 fps (NTSC)
720 x 576 x 25 fps (PAL/SECAM)
The 4:3 aspect ratio on standard TV and computer screens (left) is more square than the 16:9 ratio of wide screen sets (right). (Image courtesy of Intergraph Computer Systems.)
|
