High Definition Television

      High-definition television (HDTV) is a digital television broadcasting system with greater resolution than traditional television systems (NTSC, SECAM, PAL). High-definition television (HDTV) provides a resolution that is substantially higher than that of standard-definition television.

     HDTV is digitally broadcast because digital television (DTV) requires less bandwidth if sufficient video compression is used. HDTV uses 16:9 widescreen as is its aspect ratio so widescreen pictures are transmitted properly and not letter boxed or panned.

     There are three key differences between HDTV and what's become known as standard definition TV ie regular NTSC, PAL or SECAM. The three differences are; an increase in picture resolution, 16:9 widescreen as standard, and the ability to support multi-channel audio such as Dolby Digital.

     Standard definition NTSC broadcasts have 525 horizontal lines, and PAL broadcasts are slightly better at 625 lines. In both these systems however, the actual number of lines used to display the picture, known as the active lines, is fewer than that. In addition, both PAL and NTSC systems are interlaced, that is, each frame is split into two fields, one field is the odd-numbered lines and the other is the even lines. Each frame is displayed alternately and our brain puts them together to create a complete image of each frame. This has an adverse affect on picture quality.