High Definition TV

ibn 11-24-08

High-definition television (HDTV) is a digital television broadcasting system with higher resolution than traditional television systems “standard-definition” TV, or SDTV). HDTV is digitally broadcast; the earliest implementations used analog broadcasting, but today digital television (DTV) signals are used, requiring less bandwidth due to digital video compression.

As soon as the MPEG-1 standard provided the foundation for digital TV, development of modern TV standards started worldwide. After finalization of MPEG-2 in mid 1993, the DVB organisation within the International Telecommunication Union’s radio telecommunications sector (ITU-R) developed the ETSI standard 300-327 by the end of December 1993.

It became known as DVB-T for digital terrestrial TV. DVB-S and DVB-C standards soon followed for terrestrial, satellite and cable transmission of SDTV and HDTV. In the USA the Grand Alliance proposed ATSC as the new standard for SDTV and HDTV. Both ATSC and DVB were based on the MPEG-2 standard. The DVB-S2 standard is based on the newer and more efficient H.264/MPEG-4 AVC compression standards. Common for all DVB standards is the use of highly efficient modulation techniques for further reducing bandwidth, and foremost for reducing receiver-hardware and antenna requirement.

In 1983, the International Telecommunication Union’s radio telecommunications sector (ITU-R) set up a working party (IWP11/6) with the aim of setting a single international HDTV standard.

Initially the existing 5:3 aspect ratio had been the main candidate, but due to the influence of widescreen cinema, the aspect ratio 16:9 (1.78) eventually emerged as being a reasonable compromise between 5:3 (1.67) and the common 1.85 widescreen cinema format. (It has beensuggested that the 16:9 ratio was chosen as being the geometric mean of 4:3, Academy Ratio, and 2.35:1, the widest cinema format in common use, in order to minimise wasted screen space when displaying content with a variety of aspect ratios.)

An aspect ratio of 16:9 was duly agreed at the first meeting of the WP at the BBC’s R & D establishment in Kingswood Warren. The resulting ITU-R Recommendation ITU-R BT.709-2 (“Rec. 709”) includes the 16:9 aspect ratio, a specified colorimetry, and the scan modes 1080i (1,080 actively-interlaced lines of resolution) and 1080p (1,080 progressively-scanned lines). The current BBC freeview trials of HD use MBAFF, which contains both progressive and interlaced content in the same encoding.


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