OTHER TECH

While America's digital TV (DTV) system offers plenty of options for broadcasting programs, the only formats you need to be aware of are 1080i (interlaced) and 720p (progressive-scan) high-definition TV and 480p and 480i standard-definition TV. Any off-air DTV tuner you buy will be able to handle broadcasts in all four formats and display a standard- or high-def image on your set. The stations and cable channels listed in this guide provide at least some programs in 1080i or 720p.

The two HDTV formats differ in the number of lines of vertical resolution they provide: 1,080 for 1080i and 720 for 720p. In interlaced programs, the lines in each video frame are divided into two alternating fields that are "drawn" on the screen sequentially. This process happens so fast that your eyes fill in the gaps. With progressive-scan programs, all the lines in each video frame appear onscreen together. HDTV programs are produced with a 16:9 aspect ratio - the same shape as widescreen HDTV displays and similar to a movie theater screen. In comparison, standard-definition programs have only 480 lines of vertical resolution - effectively equivalent to a DVD: 480p is scanned progressively and 480i is interlaced. Standard-def programs can use either the widescreen 16:9 or the standard, squarish 4:3 aspect ratio.

- Al Griffin