Analogue television uses a 6 MHz signal- carrying intensity and colour information for each scan line of the picture. An analogue signal in the U.S. has 480 scan lines (525 broadcast) in NTSC format and in Europe; the PAL format has 576 visible lines (650 transmitted). This level of resolution was good fifty years ago, but today most electronic technologies have moved to higher-resolution digital. Computer monitors offer resolutions of at least 1280x1024, leaving analogue pale in comparison.
New satellite systems and DVDs that use a digital encoding scheme provide clearer pictures, but this is then converted to analogue to be displayed on most televisions. HDTV is the big push to convert the world of television from analogue to digital in order to forgo this conversion process and use the signals from the DVD, TV signal, Satellite or Internet directly.
5.1 Digital Stereo improves sound quality by using one woofer and five speakers to deliver crystal clear surround sound. HDTV has a high resolution of either 720 or 1080 scan lines. In Europe, the move is towards the scanned 720 lines on the TV. Progressive scanning updates the screen 60 times a minute, whereas the interlaced 1080 line scans cause alternate lines to update 60 times a minute, leading to flickering on large displays.
TV Stations may choose which formats to broadcast. ...
TV Stations may choose which formats to broadcast. The HDTV formats in use are 720p - 1280x720 pixels progressive, 1080i - 1920x1080 pixels interlaced and 1080p - 1920x1080 pixels progressive among others.
"It is always optimum to reproduce video material in the same origination format" advises TV designer Ed Milbourn. "Optimum production and delivery for 1080p is 60 frames."
Processing the digital quality through current analogue bandwidths require compression of the digital information via special technologies. The US after defining the ATSC standards, uses the MPEG-2 compression in DVDs. This offers a lossful compression of 55:1, squeezing the digital picture in the same 6-megahertz (MHz) analogue transmission bandwidth. Compression reduces image quality from the original digital camera image. MPEG-2 is competent at removing details that the human eye ignores anyway. The quality of the image becomes significantly better than traditional analogue. Europe plans to use the H.264 codec in the MPEG-4 standard.
The 16:9 aspect wide ratios compared to the previous 4:3 ratio shows that the HDTV image is aligned to the three-decade old aspect ratios used in movie theatres. The panoramic view fills the eyes better than the 4:3 ratios, aligned to the format of its 35-mm film base.
These benefits apart, HDTV can also offer Interactive TV, due to the fact that almost every station already sends data with signals. Closed captioning and descriptive audio are existing interactivity, but replay TV and other menu-based options embedded in the broadcast signal will take interactivity to a new level in HDTV.
HDTV media delivery: hardware and software
Changes to TV transmission