History of high-definition television
In 1949, France launched 819 lines television, first high definition public television network (778 active lines). This 819 lines network remained operational until 1983.

In 1958, the U.S.S.R. created Трансформатор (Transformer), the first high-resolution (definition) television system capable of producing an image composed of 1,125 lines of resolution for the purpose of televison conferences among military commands; as it was a military product, it was not commercialised.[3]

In 1969, Nippon Hōsō Kyōkai (NHK) first developed commercial, high-definition television, [4] yet, the system was not commercialized until late in the 1990s.

In 1983, the International Telecommunication Union ITU-R set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. This WP considered many views and through the 1980s served to encourage development in a number of video digital processing areas such as conversion between 30/60 and 25/50 picture rates using motion vectors that lead to other outcomes. While a single standard was never finalized, a common aspect ratio of 16:9 was agreed to at the first meeting at the BBC's R & D establishment at Kingswood Warren. Initially the Japanese 5:3 ratio was considered but a proposal to widen it to 5 1/3:3 = 16:9 was accepted. The ITU-R Recommendation BT.709 includes 16:9, colorimetry and the 1080i (1,080 actively-interlaced lines of resolution) and the 1080p (1,080 progressively-scanned lines). It also included the 1440 x 1152 HDMAC scanning format. 720p formats were strongly resisted by some ITU-R members and were not standardized there. Both 1920 x 1080 and 1280 x 720p (720 progressively-scanned lines), systems for a range of frame and field rates are also defined by several SMPTE standards.

Projection screen in a home theater, displaying a high-definition television image.High-definition television refers to the image resolution and, loosely, to photo- and videographic media capable of such image resolution, i.e. photographic film and digital video. Current HDTV broadcast standards are in the ATSC and DVB specifications. HDTV is capable of cinema-quality audio, because it uses the Dolby Digital (AC-3) format to support the 5.1 surround sound system.

HDTV sources
The rise in popularity of large screens and projectors has made the limitations of conventional Standard Definition TV (SDTV) increasingly evident. An HDTV compatible television set will not improve the quality of SDTV channels. To get a better picture HDTV televisions require a High Definition (HD) signal. Typical sources of HD signals are as follows:

Over the air with an antenna. Most cities in the US with major network affiliates broadcast over the air in HD. To receive this signal an HD tuner is required. Most newer HDTV televisions have an HD tuner built in. For HDTV televisions without a built in HD tuner, a separate set-top HD tuner box can be rented from a cable or satellite company or purchased.
Cable television companies often offer HDTV broadcasts as part of their digital broadcast service. This is usually done with a set-top box or CableCARD issued by the cable company. Alternatively one can usually get the network HDTV channels for free with basic cable by using a QAM tuner built into their HDTV or set-top box. Some cable carriers also offer HDTV on-demand playback of movies and commonly viewed shows.
Satellite-based TV companies, such as DirecTV and Dish Network (both in North America), Sky Digital (in the UK and Ireland) and Bell ExpressVu (in Canada), offer HDTV to customers as an upgrade. New satellite receiver boxes and a new satellite dish are often required to receive HD content.
Video game systems, such as the Xbox (NTSC only), Xbox 360, and Playstation 3, can output an HD signal. The Xbox Live Marketplace service offers HD movies, TV shows, movie trailers, and clips for download to Xbox 360 consoles.
Most newer computer graphics cards have either HDMI or DVI interface, which can be used to output image to HDTV television.
Two optical disc standards, Blu-ray and HD DVD, can provide enough digital storage to store hours of HD video content.

Notation
HDTV broadcast systems are defined three-fold, by:

The number of lines in the vertical display resolution.
The scanning system: progressive scanning (p) or interlaced scanning (i). Progressive scanning redraws an image frame (all of its lines) per each image refreshing. Interlaced scanning redraws the image field (every second line) per each image refreshing, and then redraws the remaining lines with a second refreshing. Interlaced scanning yields greater image resolution using a narrower bandwidth, but suffers flicker and artifacts.
The number of frames per second or fields per second.
The 720p60 format is 1280 × 720 pixels, progressive encoding with 60 fields per second (60 Hz). The 1080i50 format is 1920 × 1080 pixels, interlaced encoding with 50 fields (25 frames) per second. For commercial naming of the product, either the frame rate or the field rate is dropped, e.g. a "1080i television set" label indicates only the image resolution.[5] Often, the rate is inferred from the context, usually assumed to be either 50 or 60, except for 1080p, which denotes 1080p24, 1080p25, and 1080p30, but also 1080p50 and 1080p60 in the future.

A frame or field rate can also be specified without a resolution. For example 24p means 24 progressive scan frames per second and 50i means 25 interlaced frames per second, consisting of 50 interlaced fields per second. Most HDTV systems support some standard resolutions and frame or field rates. The most common are noted below.

Changes in notation
The terminology described above was invented for digital systems in the 1990s. A digital signal encodes the color of each pixel, or dot on the screen as a series of numbers. Before that, analog TV signals encoded values for one monochrome, or three-color signals as they scanned a screen continuously from line to line. By comparison, radio encodes an analog signal of the sound to be sent to an amplified speaker, typically up to 20 kHz, but video signals are in the MHz range, which is why they are much higher in the broadcast spectrum than audio radio. Analog video signals have no true "pixels" to measure horizontal resolution. The vertical scan-line count included off-screen scan lines with no picture information while the CRT beam returned to the top of the screen to begin another field. Thus NTSC was considered to have "525 lines" even though only 486 of them had a picture (625/576 for PAL). Similarly the Japanese MUSE system was called "1125 line", but is only 1035i by today's measuring standards. This change was made because digital systems have no need of blank retrace lines unless the signal was converted to analog to drive a CRT.

Standard resolutions

When resolution is considered, both the resolution of the transmitted signal and the (native) displayed resolution of a TV set are taken into account. Digital NTSC- and PAL/SECAM-like signals (480i60 and 576i50 respectively) are transmitted at a horizontal resolution of 720 or 704 "pixels". However these transmitted DTV "pixels" are not square, and have to be stretched for correct viewing. PAL TV sets with an aspect ratio of 4:3 use a fixed pixel grid of 768 × 576 or 720 × 540; with an aspect ratio of 16:9 they use 1440 x 768, 1024 × 576 or 960 × 540; NTSC ones use 640 × 480 and 852 × 480 or, seldom, 720 × 540. High Definition usually refers to one million pixels or more.

In Australia, the 576p50 format is also considered a HDTV format, as it has higher vertical resolution though the use of progressive scanning. When Australia started DVB-T in 2001 several networks broadcast high-definition in a 576p format as this could give better quality on 50Hz scanning CRT TVs and was not as demanding on MPEG-2 bit-rate. Now that flat-screens are predominating and these have an interlace to progressive scan conversion there is little difference in picture quality. Also MPEG-2 encoders have improved so the more conventional 720p and 1080i formats are now used. Technically, the 576p format is internationally defined as Enhanced-definition television and many DVD players can provide a 576p signal usually on HDMI outputs.

Standard frame or field rates
23.976p (allow easy conversion to NTSC)
24p (cinematic film)
25p (PAL, SECAM DTV progressive material)
30p (29.97p in drop frame) (NTSC DTV progressive material)
50p (PAL, SECAM DTV progressive material)
60p (59.94p in drop frame) (NTSC DTV progressive material)
50i (PAL & SECAM)
60i (59.94i in drop frame) (NTSC, PAL-M)