Mechanical . This schematic shows the circular paths traced by the holes that may also be square for greater precision. The area of the disk outlined in black displays the region scanned.
Facsimile transmission systems for still photographs pioneered methods of mechanical scanning of images in the early 19th century.
Alexander Bain introduced the facsimile machine between 1843 and 1846.
Frederick Bakewell demonstrated a working laboratory version in 1851.
Willoughby Smith discovered the
photoconductivity of the element
selenium in 1873. As a 23-year-old German university student,
Paul Julius Gottlieb Nipkow proposed and patented the
Nipkow disk in 1884 in
Berlin. This was a spinning disk with a spiral pattern of holes, so each hole scanned a line of the image. Although he never built a working model of the system, variations of Nipkow's spinning-disk "
image rasterizer" became exceedingly common.
Constantin Perskyi had coined the word
television in a paper read to the International Electricity Congress at the
International World Fair in Paris on 24 August 1900. Perskyi's paper reviewed the existing electromechanical technologies, mentioning the work of Nipkow and others. However, it was not until 1907 that developments in amplification tube technology by
Lee de Forest and
Arthur Korn, among others, made the design practical. The first demonstration of the live transmission of images was by Georges Rignoux and A. Fournier in Paris in 1909. A matrix of 64
selenium cells, individually wired to a mechanical
commutator, served as an electronic
retina. In the receiver, a type of
Kerr cell modulated the light, and a series of differently angled mirrors attached to the edge of a rotating disc scanned the modulated beam onto the display screen. A separate circuit regulated synchronization. The 8x8
pixel resolution in this proof-of-concept demonstration was just sufficient to clearly transmit individual letters of the alphabet. An updated image was transmitted "several times" each second. In 1911,
Boris Rosing and his student
Vladimir Zworykin created a system that used a mechanical mirror-drum scanner to transmit, in Zworykin's words, "very crude images" over wires to the "
Braun tube" (
cathode-ray tube or "CRT") in the receiver. Moving images were not possible because, in the scanner: "the sensitivity was not enough and the selenium cell was very laggy". In 1921,
Édouard Belin sent the first image via radio waves with his
belinograph. in 1925 with his televisor equipment and dummies "James" and "Stooky Bill"
(right) By the 1920s, when amplification made television practical, Scottish inventor
John Logie Baird employed the Nipkow disk in his prototype video systems. On 25 March 1925, Baird gave the first public demonstration of televised
silhouette images in motion at
Selfridges's department store in London. Since human faces had inadequate contrast to show up on his primitive system, he televised a ventriloquist's dummy named "Stooky Bill", whose painted face had higher contrast, talking and moving. By 26 January 1926, he had demonstrated before members of the Royal Institution the transmission of an image of a face in motion by radio. This is widely regarded as the world's first true public television demonstration, exhibiting light, shade, and detail. Baird's system used the Nipkow disk for both scanning the image and displaying it. A brightly illuminated subject was placed in front of a spinning Nipkow disk set with lenses that swept images across a static photocell. The
thallium sulfide (thalofide) cell, developed by
Theodore Case in the U.S., detected the light reflected from the subject and converted it into a proportional electrical signal. This was transmitted by AM radio waves to a receiver unit, where the video signal was applied to a neon light behind a second Nipkow disk rotating synchronized with the first. The brightness of the neon lamp was varied in proportion to the brightness of each spot on the image. As each hole in the disk passed by, one
scan line of the image was reproduced. Baird's disk had 30 holes, producing an image with only 30 scan lines, just enough to recognize a human face. In 1927, Baird transmitted a signal over of telephone line between London and
Glasgow. Baird's original 'televisor' now resides in the Science Museum, South Kensington. In 1928, Baird's company (Baird Television Development Company/Cinema Television) broadcast the first transatlantic television signal between London and New York and the first shore-to-ship transmission. In 1929, he became involved in the first experimental mechanical television service in Germany. In November of the same year, Baird and
Bernard Natan of
Pathé established France's first television company, Télévision-
Baird-Natan. In 1931, he made the first outdoor remote broadcast of
The Derby. In 1932, he demonstrated
ultra-short wave television. Baird's mechanical system reached a peak of 240 lines of resolution on
BBC telecasts in 1936, though the mechanical system did not scan the televised scene directly. Instead, a
17.5 mm film was shot, rapidly developed, and then scanned while the film was still wet. A US inventor,
Charles Francis Jenkins, also pioneered the television. He published an article on "Motion Pictures by Wireless" in 1913, transmitted moving silhouette images for witnesses in December 1923, and on 13 June 1925, publicly demonstrated synchronized transmission of silhouette pictures. In 1925, Jenkins used the Nipkow disk and transmitted the silhouette image of a toy windmill in motion over a distance of 5 miles (8 km), from a naval radio station in Maryland to his laboratory in Washington, D.C., using a lensed disk scanner with a 48-line resolution. He was granted
U.S. Patent No. 1,544,156 (Transmitting Pictures over Wireless) on 30 June 1925 (filed 13 March 1922).
Herbert E. Ives and
Frank Gray of
Bell Telephone Laboratories gave a dramatic demonstration of mechanical television on 7 April 1927. Their reflected-light television system included both small and large viewing screens. The small receiver had a 2-inch-wide by 2.5-inch-high screen (5 by 6 cm). The large receiver had a screen 24 inches wide by 30 inches high (60 by 75 cm). Both sets could reproduce reasonably accurate, monochromatic, moving images. Along with the pictures, the sets received synchronized sound. The system transmitted images over two paths: first, a
copper wire link from Washington to New York City, then a radio link from
Whippany, New Jersey. Comparing the two transmission methods, viewers noted no difference in quality. Subjects of the telecast included
Secretary of Commerce Herbert Hoover. A
flying-spot scanner beam illuminated these subjects. The scanner that produced the beam had a 50-aperture disk. The disc revolved at a rate of 18 frames per second, capturing one frame about every 56
milliseconds. (Today's systems typically transmit 30 or 60 frames per second, or one frame every 33.3 or 16.7 milliseconds, respectively.) Television historian Albert Abramson underscored the significance of the Bell Labs demonstration: "It was, in fact, the best demonstration of a mechanical television system ever made to this time. It would be several years before any other system could even begin to compare with it in picture quality." In 1928,
WRGB, then W2XB, was started as the world's first television station. It broadcast from the
General Electric facility in
Schenectady, NY. It was popularly known as "
WGY Television." Meanwhile, in the
Soviet Union,
Leon Theremin had been developing a mirror drum-based television, starting with 16 lines resolution in 1925, then 32 lines, and eventually 64 using
interlacing in 1926. As part of his thesis, on 7 May 1926, he electrically transmitted and then projected near-simultaneous moving images on a screen. On 25 December 1926,
Kenjiro Takayanagi demonstrated a television system with a 40-line resolution that employed a Nipkow disk scanner and CRT display at Hamamatsu Industrial High School in Japan. This prototype is still on display at the Takayanagi Memorial Museum in
Shizuoka University, Hamamatsu Campus. His research in creating a production model was halted by the
SCAP after
World War II. Because only a limited number of holes could be made in the disks, and disks beyond a certain diameter became impractical, image resolution on mechanical television broadcasts was relatively low, ranging from about 30 lines up to 120 or so. Nevertheless, the image quality of 30-line transmissions steadily improved with technical advances, and by 1933 the UK broadcasts using the Baird system were remarkably clear. A few systems ranging into the 200-line region also went on the air. Two of these were the 180-line system that Compagnie des Compteurs (CDC) installed in Paris in 1935 and the 180-line system that
Peck Television Corp. started in 1935 at station VE9AK in
Montreal. The advancement of all-electronic television (including
image dissectors and other camera tubes and
cathode-ray tubes for the reproducer) marked the start of the end for mechanical systems as the dominant form of television. Mechanical television, despite its inferior image quality and generally smaller picture, would remain the primary television technology until the 1930s. The last mechanical telecasts ended in 1939 at stations run by a lot of public universities in the United States.
Electronic In 1897, English physicist
J. J. Thomson was able, in his three well-known experiments, to deflect cathode rays, a fundamental function of the modern
cathode-ray tube (CRT). The earliest version of the CRT was invented by the German physicist
Ferdinand Braun in 1897 and is also known as the "Braun" tube. It was a
cold-cathode diode, a modification of the
Crookes tube, with a
phosphor-coated screen. Braun was the first to conceive the use of a CRT as a display device. The
Braun tube became the foundation of 20th century television. In 1906 the Germans Max Dieckmann and Gustav Glage produced
raster images for the first time in a CRT. In 1907, Russian scientist
Boris Rosing used a CRT in the receiving end of an experimental
video signal to form a picture. He managed to display simple geometric shapes onto the screen. In 1908,
Alan Archibald Campbell-Swinton, a fellow of the
Royal Society (UK), published a letter in the scientific journal
Nature in which he described how "distant electric vision" could be achieved by using a cathode-ray tube, or Braun tube, as both a transmitting and receiving device, he expanded on his vision in a speech given in London in 1911 and reported in
The Times and the Journal of the Röntgen Society. In a letter to
Nature published in October 1926, Campbell-Swinton also announced the results of some "not very successful experiments" he had conducted with G. M. Minchin and J. C. M. Stanton. They had attempted to generate an electrical signal by projecting an image onto a selenium-coated metal plate that was simultaneously scanned by a
cathode ray beam. These experiments were conducted before March 1914, when Minchin died, but they were later repeated by two different teams in 1937, by H. Miller and J. W. Strange from
EMI, and by H. Iams and A. Rose from
RCA. Both teams successfully transmitted "very faint" images with the original Campbell-Swinton's selenium-coated plate. Although others had experimented with using a cathode-ray tube as a receiver, the concept of using one as a transmitter was novel. The first cathode-ray tube to use a
hot cathode was developed by
John B. Johnson (who gave his name to the term
Johnson noise) and Harry Weiner Weinhart of
Western Electric, and became a commercial product in 1922. In 1926, Hungarian engineer
Kálmán Tihanyi designed a television system using fully electronic scanning and display elements and employing the principle of "charge storage" within the scanning (or "camera") tube. The problem of low sensitivity to light resulting in low electrical output from transmitting or "camera" tubes would be solved with the introduction of charge-storage technology by Kálmán Tihanyi beginning in 1924. His solution was a camera tube that accumulated and stored electrical charges ("photoelectrons") within the tube throughout each scanning cycle. The device was first described in a patent application he filed in
Hungary in March 1926 for a television system he called "Radioskop". After further refinements included in a 1928 patent application, so he applied for patents in the United States. Although his breakthrough would be incorporated into the design of
RCA's "
iconoscope" in 1931, the U.S. patent for Tihanyi's transmitting tube would not be granted until May 1939. The patent for his receiving tube had been granted the previous October. Both patents had been purchased by RCA prior to their approval. Charge storage remains a basic principle in the design of imaging devices for television to the present day. Takayanagi did not apply for a patent. In the 1930s,
Allen B. DuMont made the first CRTs to last 1,000 hours of use which is one of the factors that led to the widespread adoption of television. On 7 September 1927, US inventor
Philo Farnsworth's
image dissector camera tube transmitted its first image, a simple straight line, at his laboratory at 202 Green Street in San Francisco. By 3 September 1928, Farnsworth had developed the system sufficiently to hold a demonstration for the press. This is widely regarded as the first electronic television demonstration. That year, Farnsworth transmitted the first live human images with his system, including a three and a half-inch image of his wife Elma ("Pem") with her eyes closed (possibly due to the bright lighting required). demonstrates electronic television (1929). Meanwhile, Vladimir Zworykin also experimented with the cathode-ray tube to create and show images. While working for
Westinghouse Electric in 1923, he began to develop an electronic camera tube. However, in a 1925 demonstration, the image was dim, had low contrast and poor definition, and was stationary. Zworykin's imaging tube never got beyond the laboratory stage. However, RCA, which acquired the Westinghouse patent, asserted that the patent for Farnsworth's 1927 image dissector was written so broadly that it would exclude any other electronic imaging device. Thus, based on Zworykin's 1923 patent application, RCA filed a
patent interference suit against Farnsworth. The
U.S. Patent Office examiner disagreed in a 1935 decision, finding priority of invention for Farnsworth against Zworykin. Farnsworth claimed that Zworykin's 1923 system could not produce an electrical image of the type to challenge his patent. Zworykin received a patent in 1928 for a color transmission version of his 1923 patent application. He also divided his original application in 1931. Zworykin was unable or unwilling to introduce evidence of a working model of his tube that was based on his 1923 patent application. In September 1939, after losing an appeal in the courts and being determined to go forward with the commercial manufacturing of television equipment, RCA agreed to pay Farnsworth US$1 million over ten years, in addition to license payments, to use his patents. In 1933, RCA introduced an improved camera tube that relied on Tihanyi's charge storage principle. Called the "Iconoscope" by Zworykin, the new tube had a light sensitivity of about 75,000
lux, and thus was claimed to be much more sensitive than Farnsworth's image dissector. However, Farnsworth had overcome his power issues with his Image Dissector through the invention of a completely unique "
Multipactor" device that he began work on in 1930, and demonstrated in 1931. This small tube could amplify a signal reportedly to the 60th power or better and showed great promise in all fields of electronics. Unfortunately, an issue with the multipactor was that it wore out at an unsatisfactory rate. in 1933 At the
Berlin Radio Show in August 1931 in
Berlin,
Manfred von Ardenne gave a public demonstration of a television system using a CRT for both transmission and reception, the first completely electronic television transmission. However, Ardenne had not developed a camera tube, using the CRT instead as a
flying-spot scanner to scan slides and film. Ardenne achieved his first transmission of television pictures on 24 December 1933, followed by test runs for a public television service in 1934. The world's first electronically scanned television service then started in Berlin in 1935, the
Fernsehsender Paul Nipkow, culminating in the live broadcast of the
1936 Summer Olympic Games from Berlin to public places all over Germany. Philo Farnsworth gave the world's first public demonstration of an all-electronic television system, using a live camera, at the
Franklin Institute of
Philadelphia on 25 August 1934 and for ten days afterward. Mexican inventor
Guillermo González Camarena also played an important role in early television. His experiments with television (known as telectroescopía at first) began in 1931 and led to a patent for the "trichromatic field sequential system"
color television in 1940. In Britain, the
EMI engineering team led by
Isaac Shoenberg applied in 1932 for a patent for a new device they called "the Emitron", which formed the heart of the cameras that they designed for the BBC. On 2 November 1936, a
405-line broadcasting service employing the Emitron began at studios in
Alexandra Palace and transmitted from a specially built mast atop one of the Victorian building's towers. It alternated briefly with Baird's mechanical system in adjoining studios but was more reliable and visibly superior. This was the world's first regular "high-definition" television service. The original US iconoscope was noisy, had a high ratio of interference to signal, and ultimately gave disappointing results, especially compared to the high-definition mechanical scanning systems that became available. The
EMI team, under the supervision of
Isaac Shoenberg, analyzed how the iconoscope (or Emitron) produced an electronic signal and concluded that its real efficiency was only about 5% of the theoretical maximum. They solved this problem by developing and patenting in 1934 two new camera tubes dubbed
super-Emitron and
CPS Emitron. The super-Emitron was between ten and fifteen times more sensitive than the original Emitron and iconoscope tubes, and, in some cases, this ratio was considerably greater. This was the first time that anyone had broadcast a live street scene from cameras installed on the roof of neighboring buildings because neither Farnsworth nor RCA would do the same until the
1939 New York World's Fair. used during the black-and-white era before 1970. It was displayed when a television station first signed on every day. On the other hand, in 1934, Zworykin shared some patent rights with the German licensee company Telefunken. The "image iconoscope" ("Superikonoskop" in Germany) was produced as a result of the collaboration. This tube is essentially identical to the super-Emitron. The production and commercialization of the super-Emitron and image iconoscope in Europe were not affected by the
patent war between Zworykin and Farnsworth because Dieckmann and Hell had priority in Germany for the invention of the image dissector, having submitted a patent application for their
Lichtelektrische Bildzerlegerröhre für Fernseher (
Photoelectric Image Dissector Tube for Television) in Germany in 1925, two years before Farnsworth did the same in the United States. The image iconoscope (Superikonoskop) became the industrial standard for public broadcasting in Europe from 1936 until 1960, when it was replaced by the
vidicon and
plumbicon tubes. Indeed, it represented the European tradition in electronic tubes competing against the American tradition represented by the image orthicon. The German company Heimann produced the Superikonoskop for the 1936 Berlin Olympic Games, later Heimann also produced and commercialized it from 1940 to 1955; finally the Dutch company
Philips produced and commercialized the image iconoscope and multicon from 1952 to 1958. U.S. television broadcasting, at the time, consisted of a variety of markets in a wide range of sizes, each competing for programming and dominance with separate technology until deals were made and standards agreed upon in 1941. RCA, for example, used only Iconoscopes in the New York area, but Farnsworth Image Dissectors in Philadelphia and San Francisco. In September 1939, RCA agreed to pay the Farnsworth Television and Radio Corporation royalties over the next ten years for access to Farnsworth's patents. With this historic agreement in place, RCA integrated much of what was best about the Farnsworth Technology into their systems. Electrical engineer
Benjamin Adler played a prominent role in the development of television. The world's first 625-line television standard was designed in the Soviet Union in 1944 and became a national standard in 1946. The first broadcast in 625-line standard occurred in Moscow in 1948. The concept of 625 lines per frame was subsequently implemented in the European
CCIR standard. In 1936,
Kálmán Tihanyi described the principle of
plasma display, the first
flat-panel display system. Early electronic
television sets were large and bulky, with
analog circuits made of
vacuum tubes. Following the invention of the first working
transistor at
Bell Labs,
Sony founder
Masaru Ibuka predicted in 1952 that the transition to
electronic circuits made of transistors would lead to smaller and more portable television sets. The first fully transistorized, portable
solid-state television set was the 8-inch
Sony TV8-301, developed in 1959 and released in 1960. This began the transformation of television viewership from a communal viewing experience to a solitary viewing experience. By 1960, Sony had sold over 4million portable television sets worldwide.
Color , sometimes used when no program material is available The basic idea of using three monochrome images to produce a color image had been experimented with almost as soon as black-and-white televisions had first been built. Although he gave no practical details, among the earliest published proposals for television was one by Maurice Le Blanc in 1880 for a color system, including the first mentions in television literature of line and frame scanning. Polish inventor
Jan Szczepanik patented a color television system in 1897, using a
selenium photoelectric cell at the transmitter and an electromagnet controlling an oscillating mirror and a moving prism at the receiver. But his system contained no means of analyzing the spectrum of colors at the transmitting end and could not have worked as he described it. Another inventor,
Hovannes Adamian, also experimented with color television as early as 1907. The first color television project is claimed by him, and was patented in Germany on 31 March 1908, patent No. 197183, then in Britain, on 1 April 1908, patent No. 7219, in France (patent No. 390326) and in Russia in 1910 (patent No. 17912). Scottish inventor
John Logie Baird demonstrated the world's first color transmission on 3 July 1928, using scanning discs at the transmitting and receiving ends with three spirals of apertures, each spiral with filters of a different primary color, and three light sources at the receiving end, with a
commutator to alternate their illumination. Baird also made the world's first color broadcast on 4 February 1938, sending a mechanically scanned 120-line image from Baird's
Crystal Palace studios to a projection screen at London's
Dominion Theatre. Mechanically scanned color television was also demonstrated by
Bell Laboratories in June 1929 using three complete systems of
photoelectric cells, amplifiers, glow-tubes, and color filters, with a series of mirrors to superimpose the red, green, and blue images into one full-color image. The first practical hybrid system was again pioneered by John Logie Baird. In 1940, he publicly demonstrated a color television combining a traditional black-and-white display with a rotating colored disk. This device was very "deep" but was later improved with a mirror folding the light path into an entirely practical device resembling a large conventional console. However, Baird was unhappy with the design, and, as early as 1944, had commented to a British government committee that a fully electronic device would be better. In 1939, Hungarian engineer
Peter Carl Goldmark introduced an electro-mechanical system while at
CBS, which contained an
Iconoscope sensor. The CBS field-sequential color system was partly mechanical, with a disc made of red, blue, and green filters spinning inside the television camera at 1,200 rpm and a similar disc spinning in synchronization in front of the cathode-ray tube inside the receiver set. The system was first demonstrated to the
Federal Communications Commission (FCC) on 29 August 1940 and shown to the press on 4 September. CBS began experimental color field tests using film as early as 28 August 1940 and live cameras by 12 November.
NBC (owned by RCA) made its first field test of color television on 20 February 1941. CBS began daily color field tests on 1 June 1941. These color systems were not compatible with existing black-and-white
television sets, and, as no color television sets were available to the public at this time, viewing of the color field tests was restricted to RCA and CBS engineers and the invited press. The
War Production Board halted the manufacture of television and radio equipment for civilian use from 22 April 1942 to 20 August 1945, limiting any opportunity to introduce color television to the general public. As early as 1940, Baird had started work on a fully electronic system he called
Telechrome. Early Telechrome devices used two electron guns aimed at either side of a phosphor plate. The phosphor was patterned so the electrons from the guns only fell on one side of the patterning or the other. Using cyan and magenta phosphors, a reasonable limited-color image could be obtained. He also demonstrated the same system using monochrome signals to produce a 3D image (called "
stereoscopic" at the time). A demonstration on 16 August 1944 was the first example of a practical color television system. Work on the Telechrome continued, and plans were made to introduce a three-gun version for full color. However, Baird's untimely death in 1946 ended the development of the Telechrome system. Similar concepts were common through the 1940s and 1950s, differing primarily in the way they re-combined the colors generated by the three guns. The
Geer tube was similar to Baird's concept, but used small pyramids with the phosphors deposited on their outside faces instead of Baird's 3D patterning on a flat surface. The
Penetron used three layers of phosphor on top of each other and increased the power of the beam to reach the upper layers when drawing those colors. The
Chromatron used a set of focusing wires to select the colored phosphors arranged in vertical stripes on the tube. One of the great technical challenges of introducing color
broadcast television was the desire to conserve
bandwidth, potentially three times that of the existing
black-and-white standards, and not use an excessive amount of
radio spectrum. In the United States, after considerable research, the
National Television Systems Committee approved an all-electronic system developed by
RCA, which encoded the color information separately from the brightness information and significantly reduced the resolution of the color information to conserve bandwidth. As black-and-white televisions could receive the same transmission and display it in black-and-white, the color system adopted is [backwards] "compatible". ("Compatible Color", featured in RCA advertisements of the period, is mentioned in the song "
America", of
West Side Story, 1957.) The brightness image remained compatible with existing black-and-white television sets at slightly reduced resolution. In contrast, color televisions could decode the extra information in the signal and produce a limited-resolution color display. The higher-resolution black-and-white and lower-resolution color images combine in the brain to produce a seemingly high-resolution color image. The NTSC standard represented a significant technical achievement. The first color broadcast (the first episode of the live program
The Marriage) occurred on 8 July 1954. However, during the following ten years, most network broadcasts and nearly all local programming continued to be black-and-white. It was not until the mid-1960s that color sets started selling in large numbers, due in part to the color transition of 1965, in which it was announced that over half of all network prime-time programming would be broadcast in color that fall. The first all-color prime-time season came just one year later. In 1972, the last holdout among daytime network programs converted to color, resulting in the first completely all-color network season. Early color sets were either floor-standing console models or tabletop versions nearly as bulky and heavy, so in practice they remained firmly anchored in one place.
GE's relatively compact and lightweight
Porta-Color set was introduced in the spring of 1966. It used a
transistor-based
UHF tuner. The first fully transistorized color television in the United States was the
Quasar television introduced in 1967. These developments made watching color television a more flexible and convenient proposition. In 1972, sales of color sets finally surpassed sales of black-and-white sets. Color broadcasting in Europe was not standardized on the
PAL format until the 1960s, and broadcasts did not start until 1967. By this point, many of the technical issues in the early sets had been worked out, and the spread of color sets in Europe was fairly rapid. By the mid-1970s, the only stations broadcasting in black-and-white were a few high-numbered UHF stations in small markets and a handful of low-power repeater stations in even smaller markets such as vacation spots. By 1979, even the last of these had converted to color. By the early 1980s, B&W sets had been pushed into niche markets, notably low-power uses, small portable sets, or for use as
video monitor screens in lower-cost consumer equipment. By the late 1980s, even these last holdout niche B&W environments had inevitably shifted to color sets.
Digital Digital television (DTV) is the transmission of audio and video by digitally processed and multiplexed signals, in contrast to the analog and channel-separated signals used by
analog television. Due to
data compression, digital television can support more than one program on the same channel bandwidth. It is an innovative service that represents the most significant evolution in television broadcast technology since color television emerged in the 1950s. Digital television's roots have been tied very closely to the availability of inexpensive, high performance
computers. It was not until the 1990s that digital television became possible. Digital television was previously not practically possible due to the impractically high
bandwidth requirements of
uncompressed digital video, requiring around 200
Mbit/s for a
standard-definition television (SDTV) signal, Interlaced scanning, which had been specifically designed for older analog CRT display technologies, scans even-numbered lines first, then odd-numbered ones. Interlaced scanning can be regarded as the first video compression model. It was partly developed in the 1940s to double the image resolution to exceed the limitations of television broadcast bandwidth. Another reason for its adoption was to limit the flickering on early CRT screens, whose phosphor-coated screens could only retain the image from the electron scanning gun for a relatively short duration. However, interlaced scanning does not work as efficiently on newer display devices such as
liquid-crystal display (LCD), for example, which are better suited to a more frequent progressive refresh rate.
Digital television transition started in the late 2000s. All governments across the world set the deadline for analog shutdown by the 2010s. Initially, the adoption rate was low, as the first digital tuner-equipped television sets were costly. However, as the price of digital-capable television sets dropped, more and more households started converting to digital television sets. The transition is expected to be completed worldwide by the mid-to-late 2010s.
Smart television The advent of digital television allowed innovations like smart television sets. A smart television, sometimes referred to as a "connected TV" or "hybrid TV", is a television set or
set-top box with integrated Internet and
Web 2.0 features and is an example of
technological convergence between computers, television sets, and set-top boxes. Besides the traditional functions of television sets and set-top boxes provided through traditional Broadcasting media, these devices can also provide Internet TV, online
interactive media,
over-the-top content, as well as
on-demand streaming media, and
home networking access. These TVs come pre-loaded with an operating system. Smart TV is not to be confused with
Internet TV,
Internet Protocol television (IPTV), or with
Web TV.
Internet television refers to receiving television content over the Internet instead of through traditional systems—terrestrial, cable, and satellite. IPTV is one of the emerging Internet television technology standards for television networks.
Web television (WebTV) is a term used for programs created by a wide variety of companies and individuals for broadcast on Internet TV. A first patent was filed in 1994 (and extended the following year) for an "intelligent" television system, linked with data processing systems, using a digital or analog network. Apart from being linked to data networks, one key point is its ability to automatically download necessary software routines according to a user's demand and process their needs. Major TV manufacturers announced the production of smart TVs only for middle-end and high-end TVs in 2015.
3D 3D television conveys
depth perception to the viewer by employing techniques such as
stereoscopic display,
multi-view display,
2D-plus-depth, or any other form of
3D display. Most modern 3D
television sets use an
active shutter 3D system or a
polarized 3D system, and some are
autostereoscopic without the need for glasses. Stereoscopic 3D television was demonstrated for the first time on 10 August 1928, by
John Logie Baird in his company's premises at 133 Long Acre, London. Baird pioneered a variety of 3D television systems using electromechanical and cathode-ray tube techniques. The first 3D television was produced in 1935. The advent of digital television in the 2000s greatly improved 3D television sets. Although 3D television sets are quite popular for watching 3D home media, such as on Blu-ray discs, 3D programming has largely failed to make inroads with the public. As a result, many 3D television channels that started in the early 2010s were shut down by the mid-2010s. According to DisplaySearch 3D television shipments totaled 41.45 million units in 2012, compared with 24.14 in 2011 and 2.26 in 2010. As of late 2013, the number of 3D TV viewers started to decline. ==Broadcast systems==