HDTV: Special Offers

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What is HDTV

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 because digital television (DTV) requires less bandwidth if sufficient video compression is used. The term high definition once described a series of television systems from the 1930s and 1940s, starting with the British 240 line and 405 line black-and-white systems introduced in 1936, and including the American 525-line NTSC system established in 1941. However, these systems were only "high definition" when compared to earlier systems.

The British high definition TV service started trials in August 1936 and a regular service in November 1936 using both the Baird 240 line and Marconi-EMI 405 line systems. The Baird system was discontinued in February 1937.

A brief itemized history of early analog HD systems follows; these would be considered standard definition television systems today.

1936: System-A, UK: 405 lines @ 50 hz, discontinued 1986 1938: Several countries used a 441 line system, France in 1956 being the last to discontinue it 1939: System-M, USA: 525 lines @ 60 hz 1952-1956: European adoption of 625 lines @ 50 hz with PAL and SECAM color coming in 1956 1956: French (monochrome) 819 line @ 50 hz system launched, discontinued 1986 All used interlacing and a 4:3 aspect ratio except the 405 line system which started as 5:4 and later changed to 4:3.

The post–WWII French 819-line black-and-white system was high definition in the contemporary sense, but was discontinued in 1986, a year after the final British 405-line broadcast. Experimental 405 line colour transmissions were made in the 1950s using a modified NTSC system.

Since the formal adoption of DVB's widescreen HDTV transmission modes in the early 2000s the 525-line NTSC (and PAL-M) systems as well as the European 625-line PAL and SECAM systems are now regarded as (so called) standard definition television systems.

High-definition television (HDTV) yields a better-quality image than standard television does, because it has a greater number of lines of resolution. The visual information is some 2-5 times sharper because the gaps between the scan lines are narrower or invisible to the naked eye.

The lower-case "i" appended to the numbers denotes interlaced; the lower-case "p" denotes progressive. The interlaced scanning method, the 1,080 lines of resolution are divided into two, the first 540 lines are painted on a frame, the second 540 lines are painted on a second frame, reducing the bandwidth. The progressive scanning method simultaneously displays all 1,080 lines of resolution at 60 frames per second, on a greater bandwidth. (See: An explanation of HDTV numbers and laymen's glossary)

Often, the broadcast HDTV video signal soundtrack is Dolby Digital 5.1 surround sound, enabling full, surround sound capabilities, while STBC television signals include either monophonic or stereophonic audio, or both. Stereophonic broadcasts can be encoded with Dolby Surround audio signal. Brasil opted to upgrade the ISDB-T Japanese standard to H.264/MPEG-4 AVC in the video compression and HE-AAC for audio compression because Dolby is not open and the royalty fees are more expensive than that of H.264 and renamed the upgraded standard to ISDB-Tb that now became the International ISDB-T standard.

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