In the 1940-ies, two broadcast television standards have emerged, dividing the world in two camps. The 525-line format was accepted in North and South America as well as Japan, while the 625-line format conquered Europe, Asia, Africa and Australia.
The 4:3 aspect ratio reflected the format chosen by the movie industry at the dawn of the century, but in the 1950-ies Hollywood developed a series of widescreen formats like Cinerama, CinemaScope, and VistaVision. A wider and larger image immersed the viewer, giving sense of “being there”. Relatively small domestic television sets could not deliver such an experience, and their level of picture detail could barely compete with 16-mm film.
The industry leaders figured that in order to re-ignite public interest to television and to boost sales, television should offer screens that are larger and wider, with greater resolution, higher contrast and better sound. In short, a new television system should have provided an experience similar to a widescreen 35-mm film.
By the late 1960s, Japan had established itself as a country oriented towards innovation and technology. Japanese companies and the Japanese government poured resources into technological development. One area of development was television broadcast. In 1964, the NHK Corporation — also known as the Japan Broadcasting Corporation — started working on a new standard for television broadcasting. After two decades of development, the system christened MUSE started its roll out in Japan. 1125 lines of vertical resolution and 5:3 screen aspect ratio ensured image quality much closer to cinematic experience compared to regular television.
The Japanese hoped that their system would replace existing television formats, and will give the Japanese electronics manufacturers marketing advantage.
In the 1980-ies the United States and the European Community started their own development of high definition television. They wanted to preserve compatibility with the existing systems and were looking for an analog or a hybrid analog-digital system. They wanted to double the number of scanning lines compared to traditional television, and to change screen aspect ratio from 4:3 to 16:9.
HD-MAC & PAL-Plus
By the beginning of 1990-ies it became apparent that the plans for European high definition switchover were slipping: too much time was being spent by the governments of European countries in discussions of a common standard. The broadcast of 1992 Winter Olympics in Albertville and Summer Olympics in Barcelona in high definition, sent to more than 700 HDTV sets installed in major European cities, was considered a successful proof of the new technology, but it did not cause a spike in public demand for it. The multi-stage roll-out plan turned out to be too complicated. Also, the broadcasters realized that the proposed new format, HD-MAC, which offered 1250 lines of resolution — required twice the bandwidth compared to the existing format. All of this effectively killed the development of HD-MAC standard for terrestrial broadcast. Instead, the German, Austrian, Swiss and British broadcasters decided to enhance the existing PAL format with wider aspect ratio and, optionally, progressive scanning. This format, called PALPlus, was launched in 1994 and slowed down the development of high definition television in Europe even further.
It was a different story on the other side of the Atlantic. From 1987 to 1991, many technical proposals were made to the Advisory Committee for Advanced Television Service, but none was selected. In 1990, the first digital high definition television system was proposed by a company called General Instrument, based on its prior research for satellite television. It was a breakthrough. The response to this submission was overwhelmingly positive. Within seven months, three other digital HDTV systems were proposed. It was found that there were major advantages in the performance of a digital HDTV system. Consequently, the Japanese analog system was turned down.
All of the digital systems produced good HDTV pictures within an existing 6 MHz terrestrial channel, but none of the systems was ready to be selected as the standard without improvements. The Advisory Committee encouraged the proponents of the four digital systems to combine their efforts. In 1993 the authors of these proposals — AT&T, Zenith Electronics, General Instrument, MIT, Philips, Thomson, David Sarnoff Research — created the Grand Alliance to unify their submissions.
In 1994 the FCC cleared the way for testing the Grand Alliance system. In the same year Japan abandoned development of its analog HDTV system, and Europe was busy rolling out PALPlus system. This meant the United States became the world leader in development of digital high definition television.
At this point the manufacturers of computer equipment expressed their interest in the digital HTDV and its applications for computers, in particular to be able to use a TV set as a computer monitor and, conversely, to be able to watch HDTV programming on a computer screen without distortion. The computer industry requested for the new HDTV standards to use progressive scanning with high enough refresh rate and with square pixels. The latter meant that a rectangle 10 pixels wide and 10 pixels high would look like a square.
To satisfy these requirements, the engineers started from ITU-R Rec. 601, a digital component video specification for standard definition video, which stipulates that for both 525-line and 625-line systems, their digital counterparts must have 720 pixels in each line. Doubling the number of pixels and adjusting this count for 16:9 aspect ratio, comes the familiar number of 1920 pixels per line. Accommodating the request of the Hollywood and computer communities for “square-pixels” meant that the number of lines should be 1920 x (9/16) = 1080.
The 720p format also derives from the “720-pixel per line” Rec. 601 specification. 720 pixels x 4/3 (resolution improvement) x 4/3 (16:9 aspect ratio adjustment) = 1280. Accommodating the request for “square-pixels”, the number of lines turned out to be 1280 x (9/16) = 720.
Both frame sizes originally were envisioned to use progressive scanning, but the Grand Alliance member companies did not have the necessary equipment ready for production. At the same time the Japanese had a full set of equipment for their analog HDTV format, which had 1035 active lines. Converting the cameras, tape recorders and TV monitors from 1035 lines into 1080 lines was a relatively simple affair, the only problem was that the Japanese format used interlaced scanning. The Japanese companies were very adamant in pursuing the Advisory Committee to allow using interlaced scanning for 1080-line mode, and they succeeded.
HDTV broadcasting commences
Public tests of digital HDTV in the U.S. started in 1996, and full public service commenced on October 28, 1998. Some broadcasters like Fox, ABC and ESPN, chose progressive-scan 720-line format (720p), while others selected interlaced 1080-line format (1080i). The quality of 1080i format depends greatly on the quality of TV’s deinterlacer, so the first decade of the 21-st century brought to fame names like Philips, Faroudja, HQV and DVDO — companies that produced deinterlacers and scalers.
By 2009, the United States effectively completed the switchover from analog NTSC over-the-air broadcast to digital ATSC family of standards.
Nowadays, HDTV in the U.S. is past its glory days. Broadcasters cram three, four, even five subchannels into one frequency channel to increase the amount of content and advertising. With bitrate as low as 5 Mbit/s the image quality barely reaches the level of DVD video. The viewers are increasingly switching to streaming services like Netflix, Hulu, Vudu and YouTube.
What is next?
In Europe, DVB-2 standard uses H.264 and H.265 encoding formats, which allows broadcasting 1080p50 and even 4K. Some European countries already have switched to 1080p50 broadcast, which offers noticeable picture quality improvement on existing FullHD television sets.
The successor to ATSC format, ATSC-3 standard uses encoding that is about four times more efficient than the 20-year old MPEG-2, and allows either to reduce the bitrate or increase the resolution. ATSC-3 already has been rolled out in South Korea, but so far the future of this new standard in the U.S. is unclear.