the transmission of moving images and sound from a source to a receiver using electronic means. Television has had a significant impact on society by extending the senses of vision and hearing beyond the constraints of physical distance. It began as a prospective medium for education and interpersonal connection in the early 20th century, but by the mid-century it had evolved into a vibrant broadcast medium, using the paradigm of broadcast radio to offer news and entertainment to people all over the world.Television is presently broadcast “over the air” via terrestrial radio waves (conventional broadcast TV); via coaxial cables (cable TV); via satellites in geostationary Earth orbit (direct broadcast satellite, or DBS, TV); via the Internet; and optically on DVDs and Blu-ray discs.
Monochrome (black-and-white) and colour technical standards for modern television were first created in the mid-twentieth century. Since then, advancements have been made regularly, and television technology has altered dramatically in the early twenty-first century.Increased picture resolution (high-definition television [HDTV]) and modifying the proportions of the television receiver to show wide-screen images received a lot of attention. In addition, digitally encoded television signals were introduced to allow interactive services and to broadcast numerous programmes in the channel space traditionally occupied by a single show.
Despite this ongoing technological advancement, the best way to understand modern television is to first master the history and concepts of monochrome television, and then to expand that knowledge to colour television. As a result, the focus of this article is on initial principles and important developments—basic knowledge required to comprehend and appreciate future technical advancements and improvements.
Color television was not a novel concept. A.A. Pof Mordvinov, a Russian physicist, invented a system of spinning Nipkow discs and concentric cylinders with slits covered by red, green, and blue filters in the late nineteenth century. He was, however, decades ahead of his time in terms of technology; even the most basic black-and-white television was still decades away. Baird demonstrated a colour system employing a Nipkow disc with three spirals of 30 holes, one spiral for each basic colour in order, in London in 1928. At the receiver, the light source consisted of two gas-discharge tubes, one of mercury vapour and helium for green and blue and a neon tube for red. The quality, on the other hand, was abysmal.
Many inventors in the early twentieth century devised colour systems that appeared to be sound on paper but required future technology. The “sequential” system was later named after their basic premise. They proposed scanning the image with three red, blue, and green filters in succession.The three components would be duplicated in rapid succession at the receiving end, so that the human eye would “see” the original multicoloured picture. Unfortunately, for the primitive television systems of the time, this solution required too fast a scanning rate. In addition, current black-and-white receivers would be unable to recreate the images. As a result, sequential systems were coined.
In the 1990s, digital television technology became widely available. A demonstration of a new analogue high-definition television (HDTV) system by NHK, Japan’s public television network, sparked professional action in the United States in 1987. The FCC responded by holding an open competition to develop American HDTV, and General Instrument Corporation (GI) stunned the industry by revealing the world’s first all-digital television system in June 1990. The GI system, designed by Korean-born engineer Woo Paik, displayed a 1,080-line colour picture on a wide-screen receiver and transmitted the necessary information for this picture over a standard television channel.Until now, the biggest impediment to making digital television was a lack of bandwidth. After digitization, even a standard-definition television (SDTV) signal would take up more than ten times the radio frequency space of traditional analogue television, which is normally broadcast on a six-megahertz channel. HDTV would have to be shrunk to around 1% of its original size in order to be a viable alternative. Once a complete frame appeared, the GI team overcame the difficulty by only communicating changes in the picture.
The FCC accepted standards suggested by the Advanced Television Systems Committee (ATSC) in late 1996 for all digital television in the United States, both high-definition and standard-definition. By May 1, 2003, all stations in the country would be transmitting digitally on a second channel, according to the FCC’s proposal. They’d continue to broadcast in analogue, and shows would be “simulcast” in both digital and analogue, allowing the public time to adjust. In 2006, analogue transmissions would be phased out, existing television sets would be rendered obsolete, and broadcasters would hand up their analogue spectrum to the government to be auctioned off for other purposes.
Principles of television systems
Human perception of motion
Equipment at the source of production, equipment in the viewer’s home, and equipment needed to transmit the television signal from the producer to the viewer are all part of a television system. As stated in the start to this page, the objective of all of this technology is to extend the human senses of vision and hearing beyond their natural limits of physical distance. As a result, a television system must be constructed to include the essential capabilities of these senses, particularly vision. The ability of the human eye to identify the brightness, colours, features, sizes, shapes, and positions of objects in a scene before it is one of the components of vision that must be examined.
The first criterion in image analysis is that the recreated image must not flicker, as flicker causes significant visual fatigue. As the brightness of the image increases, flicker becomes more noticeable.The consecutive illuminations of the picture screen should occur no less than 50 times per second if flicker is to be unobjectionable at a brightness acceptable for home viewing during daytime and evening hours. This is roughly twice the rate of image repetition required for smooth motion replication. As a result, twice as much channel space is required to eliminate flicker as would be required to portray motion.
The intricate structure of the image is the second facet of performance that must be addressed in a television system. Several million halftone dots per square foot of area can be found in a printed engraving. The dot structure must not be visible to the unaided eye even at close range in etching reproductions, as they are designed for minute scrutiny.
The shape of the image is the third item to choose in image analysis. The global picture for SDTV is a rectangle that is one-third wider than it is high, as illustrated in the figure.In the 1950s, this 4:3 ratio (or aspect ratio) was chosen to match the dimensions of standard 35-mm motion-picture film (before to the advent of wide-screen cinema) in order to televise film without wasting frame area. HDTV televisions, which were first launched in the 1980s, have a 16:9 aspect ratio, which allows for wide-screen viewing. In both SDTV and HDTV, the width of the screen rectangle is wider than its height, regardless of the aspect ratio, to accommodate the horizontal motion that is prevalent in practically all televised events.
The path through which the image structure is examined at the camera and reconstructed on the receiver screen is the fourth determination in image analysis. The pattern on normal television is a succession of parallel straight lines, each flowing from left to right and following the lines in order from top to bottom of the screen frame.The image structure is explored at a consistent speed along each line since this ensures that the transmission channel is loaded uniformly under the demands of a specific structural detail, regardless of where in the frame the detail is located. Scanning is the breakdown and reconstruction of television images line by line, left to right, top to bottom, due to its resemblance to the progression of the line of vision when reading a page of printed materials. The scanning spot, named after the focussed beam of electrons that scans the image in a camera tube and recreates it in a picture tube, is the agent that disassembles the light values along each line.
The Picture signal
The television picture signal is a sequence of electrical waves that emerges from the translation of a televised visual into its electrical counterpart. This is physically depicted in the diagram as a wave form, with the range of electrical values (voltage or current) plotted vertically and time plotted horizontally.The electrical values correspond to the image brightness at each place on the scanning line, while time is essentially the spot’s position on the line.
Distortion and interference
The signal wave form that makes up a television picture signal embodies all the picture information to be transmitted from camera to receiver screen as well as the synchronizing information required to keep the receiver andA television picture signal’s signal wave form contains all of the visual information to be conveyed from camera to receiver screen, as well as the synchronisation information needed to maintain the receiver and transmitter scanning operations in sync. Scanning activities on the transmitter are in perfect sync. As a result, the television system must provide the wave form to each receiver as correctly and without flaws as possible.Unfortunately, practically every piece of system equipment (amplifiers, cables, transmitter, transmitting antenna, receiving antenna, and receiver circuits) conspires to distort the wave form or allows it to be contaminated by “noise” (random electrical currents) or interference.
The rate at which it is possible to transfer picture information through the television channel determines the quality and quantity of television programming.If, as previously stated, the televised image is split into approximately 200,000 pixels in a few hundredths of a second, the electrical impulses corresponding to the pixels must move over the channel at a rate of several million per second. Furthermore, the real rate of delivering picture information varies significantly from frame to frame, ranging from basic close-up shots with little fine detail to full distant scenes in which the system’s limiting detail comes into play.As a result, the television channel must be able to handle data over a continuous spectrum of frequencies that spans several million cycles. This is evidence of the human sense of sight’s exceptional comprehension. Sound conveyed through a channel merely 10,000 cycles wide, on the other hand, satisfies the ear.
Compatible colour television
Compatible colour television is the apex of electronic technology, carefully matching the demands of human perception with the demands of technological efficiency. Extra information must be added to the basic monochrome television signal, as discussed above, in order to transmit colour visuals. At the same time, this more complicated colour signal must be “compatible” with black-and-white television in order for all sets to pick up and display the same transmission. The development of interoperable colour systems in the 1950s was a true feat of electrical engineering. The fact that the standards chosen at the time are still in use attests to their quality.
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