Inaugural HDTV broadcast in the United States

HDTV technology was introduced in the United States in the 1990s by the Digital HDTV Grand Alliance, a group of television, electronic equipment, communications companies and the Massachusetts Institute of Technology.Field testing of HDTV at 199 sites in the United States was completed August 14, 1994.The first public HDTV broadcast in the United States occurred on July 23, 1996 when the Raleigh, North Carolina television station WRAL-HD began broadcasting from the existing tower of WRAL-TV south-east of Raleigh, winning a race to be first with the HD Model Station in Washington, D.C., which began broadcasting July 31, 1996 with the callsign WHD-TV, based out of the facilities of NBC owned and operated station WRC-TV. The American Advanced Television Systems Committee (ATSC) HDTV system had its public launch on October 29, 1998, during the live coverage of astronaut John Glenn’s return mission to space on board the Space Shuttle Discovery.The signal was transmitted coast-to-coast, and was seen by the public in science centers, and other public theaters specially equipped to receive and display the broadcast.

 European HDTV broadcasts

Although HDTV broadcasts had been demonstrated in Europe since the early 1990s,^{[citation needed]} the first regular broadcasts started on January 1, 2004 when the Belgian company Euro1080 launched the HD1 channel with the traditional Vienna New Year’s Concert. Test transmissions had been active since the IBC exhibition in September 2003, but the New Year’s Day broadcast marked the official start of the HD1 channel, and the start of HDTV in Europe.

Euro1080, a division of the Belgian TV services company Alfacam, broadcast HDTV channels to break the pan-European stalemate of “no HD broadcasts mean no HD TVs bought means no HD broadcasts …” and kick-start HDTV interest in Europe.The HD1 channel was initially free-to-air and mainly comprised sporting, dramatic, musical and other cultural events broadcast with a multi-lingual soundtrack on a rolling schedule of 4 or 5 hours per day.

These first European HDTV broadcasts used the 1080i format with MPEG-2 compression on a DVB-S signal from SES’s Astra 1H satellite. Euro1080 transmissions later changed to MPEG-4/AVC compression on a DVB-S2 signal in line with subsequent broadcast channels in Europe.

The number of European HD channels and viewers has risen steadily since the first HDTV broadcasts, with SES’s annual Satellite Monitor market survey for 2010 reporting more than 200 commercial channels broadcasting in HD from Astra satellites, 185 million HD-Ready TVs sold in Europe (£60 million in 2010 alone), and 20 million households (27% of all European digital satellite TV homes) watching HD satellite broadcasts (16 million via Astra satellites).

In December 2009 the United Kingdom became the first European country to deploy high definition content on digital terrestrial television (branded as Freeview) using the new DVB-T2 transmission standard as specified in the Digital TV Group (DTG) D-book. The Freeview HD service currently contains 4 HD channels and is now rolling out region by region across the UK in accordance with the digital switchover process. Some transmitters such as the Crystal Palace transmitter are broadcasting the Freeview HD service ahead of the digital switchover by means of a temporary, low-power pre-DSO multiplex.

 Notation

HDTV broadcast systems are identified with three major parameters:

• Frame size in pixels is defined as number of horizontal pixels × number of vertical pixels, for example 1280 × 720 or 1920 × 1080. Often the number of horizontal pixels is implied from context and is omitted, as in the case of 720p and 1080p.
• Scanning system is identified with the letter p for progressive scanning or i for interlaced scanning.
• Frame rate is identified as number of video frames per second. For interlaced systems an alternative form of specifying number of fields per second is often used.^{[citation needed]}

If all three parameters are used, they are specified in the following form: [frame size][scanning system][frame or field rate] or [frame size]/[frame or field rate][scanning system].^{[citation needed]} Often, frame size or frame rate can be dropped if its value is implied from context. In this case the remaining numeric parameter is specified first, followed by the scanning system.

For example, 1920×1080p25 identifies progressive scanning format with 25 frames per second, each frame being 1,920 pixels wide and 1,080 pixels high. The 1080i25 or 1080i50 notation identifies interlaced scanning format with 25 frames (50 fields) per second, each frame being 1,920 pixels wide and 1,080 pixels high. The 1080i30 or 1080i60 notation identifies interlaced scanning format with 30 frames (60 fields) per second, each frame being 1,920 pixels wide and 1,080 pixels high. The 720p60 notation identifies progressive scanning format with 60 frames per second, each frame being 720 pixels high; 1,280 pixels horizontally are implied.

50 Hz systems support three scanning rates: 25i, 25p and 50p. 60 Hz systems support a much wider set of frame rates: 23.976p, 24p, 29.97i/59.94i, 29.97p, 30p, 59.94p and 60p. In the days of standard definition television, the fractional rates were often rounded up to whole numbers, e.g. 23.976p was often called 24p, or 59.94i was often called 60i. 60 Hz high definition television supports both fractional and slightly different integer rates, therefore strict usage of notation is required to avoid ambiguity. Nevertheless, 29.97i/59.94i is almost universally called 60i, likewise 23.976p is called 24p.

For commercial naming of a product, the frame rate is often dropped and is implied from context (e.g., a 1080i television set). A frame 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.

There is no standard for HDTV colour support. Until recently the color of each pixel was regulated by three 8-bit color values, each representing the level of red, blue, and green which defined a pixel colour. Together the 24 total bits defining colour yielded just under 17 million possible pixel colors. Recentlysome manufacturers have produced systems that can employ 10 bits for each colour (30 bits total) which provides for a palette of 1 billion colors, saying that this provides a much richer picture, but there is no agreed way to specify that a piece of equipment supports this feature. Human vision can only discern approximately 1 million colours so an expanded colour palette is of questionable benefit to consumers.

article from /en.wikipedia.org

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