High-definition television (or 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.

History of high-definition television

The term high definition once described a series of television systems originating from the late 1930s, 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
• 1949: French (monochrome) 819 line @ 50 Hz system launched, discontinued 1983
• 1952-1956: European adoption of 625 lines @ 50 Hz with PAL and SECAM color coming in 1967

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 1983, before the final British 405-line broadcast. Experimental 405 line color transmissions were made in the 1950s using a modified NTSC system.

Since the formal adoption of Digital Video Broadcasting's (DVB) 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 standard definition television systems. In Australia, the 625-line digital progressive system (with 576 active lines) is officially recognized as high definition.

Color

In Mexico, Guillermo González Camarena (1917–1965), invented an early color television transmission system. He received patents for color television systems in 1942 (U.S. Patent 2,296,019), 1960 and 1962. The 1942 patent (filed in Mexico on August 19, 1940) was for a synchronized color filter wheel adapter for monochrome television, similar to the field sequential color receiver demonstrated by Baird in England in July 19391 and by CBS in the United States in August 1940.