A picture on the TV screen is formed by a large number of small dots called pixels. The higher the number of pixels, the better the picture quality will be. The pictures of conventional analogue TV broadcasting provide a maximum of 720 (horizontal) x 576 (vertical) pixels. Typically HDTV broadcasts have a resolution of at least 1280 horizontal pixels and 720 vertical pixels, providing superior picture quality over analogue TV broadcasts.
HDTV pictures are usually displayed on a wide screen (aspect ratio 16:9, i.e. the ratio of picture width to height) format, instead of the usual square screen (aspect ratio 4:3) format of conventional analogue TV pictures.
Together with the ability to support multi-channel sound systems, HDTV broadcasts enable viewers at home to have an experience comparable to watching a movie in a cinema.
Standard definition TV (SDTV) broadcasting can be considered the digital version of the conventional analogue TV broadcasting, both of which have the same screen format and picture resolution. However, digital SDTV pictures are free from the 'ghosting' and 'snowing' commonly found in analogue TV pictures.
SDTV and HDTV are two of the main features supported by digital TV.