colour television
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What is colour television?
Color television is the electronic transmission of moving color images and sound from a source to a receiver. The technology for modern color TV was developed in the mid-20th century and has improved since then. Digital television has largely replaced analog technology in the early 21st century.
The color television signal consists of two components:
* Luminance Brilliance
* Chrominance Consists of hue (color) and saturation (intensity)The television camera creates three picture signals that represent the amounts of the three primary colors (blue, green, and red) present at each point in the image pattern. Electronic circuits manipulate these three primary-color signals to derive the luminance and chrominance components.
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How does colour television differ from black-and-white television?
Color television differs from black-and-white television through its use of extra signals that transmit color information, or chrominance, in addition to the luminance (brightness) signal that is used in black and white TVs. The chrominance signal includes both hue (color) and saturation (intensity of color). Color television transmits three primary-color signals (red, green and blue), which are then converted into luminance and chrominance signals. The chrominance signal is added to the luminance signal, and the composite signal is imposed on the carrier wave. This allows black-and-white TVs to receive a signal from color television broadcasts.
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How are the three primary colours used to create images on a television screen?
Color televisions use the additive process to create colors on screens. Each pixel on the screen has three small dots of phosphors that emit red, green, and blue light when activated by an electron beam.
The three primary color signals are transmitted together. The receiving tube contains three electron guns that correspond to each primary-color signal. The screen comprises a grid of tiny triangles of discrete phosphors, one for each primary color. Every 1/60 of a second, the receiver’s three electron guns paint the entire picture simultaneously with red, green, and blue, from left to right, line by line. The color dots are small and uniformly dispersed, so the eye doesn't detect their separate presence. The primary colors in the three images mix in the viewer's mind, resulting in a full-color image.
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What are the main electronic parts inside a colour television?
A color television contains several electronic parts that work together to display images. The main components include:
- Tuner: Selects the desired channel.
- Radio-frequency amplifier: Amplifies the incoming picture and sound carriers.
- Superheterodyne mixer: Transposes the frequencies of the sound and picture carriers to intermediate frequencies.
- Intermediate-frequency amplifiers: Increases the voltage of the picture and sound carriers.
- Video detector: Separates the picture and sound signals.
- Sound intermediate amplifier and frequency detector: Converts the frequency modulation back to an audio signal current.
- Video amplifiers: Applies the luminance component of the picture signal to the electron guns.
- Synchronous detector: Separates the horizontal and vertical synchronizing pulses.
- Deflection generators: Produces the currents that flow through the electromagnetic coils in the picture tube, causing the scanning spot to be deflected across the viewing screen in the standard scanning pattern.
- Electron guns: Generate electron beams that strike the phosphor screen to produce light.
- Shadow mask/aperture grille: Ensures that the electron beams hit the correct color phosphors.
- Power-converting circuits: Converts AC power to the DC voltages needed by the circuits.
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How do electronic signals get turned into colourful pictures?
In color television, electronic signals are transformed into colorful pictures through a combination of electronic processes and the properties of light.
First, the television camera captures the scene, separating it into three primary color signals: red, green, and blue. These signals are then processed by a color coder, which converts the primary color signals into luminance (brightness) and chrominance (color) signals. The chrominance signal has two components: hue (color) and saturation (intensity of color). These components are then combined to form the overall color picture signal.
The color picture tube has three sets of phosphor dots that glow in red, blue, and green when struck by electron beams. Each beam is controlled by the corresponding primary color signal. By varying the intensity of each electron beam, a wide range of colors can be created on the screen.
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What are some advancements in colour television technology over time?
Color television has undergone significant advancements since its inception. Early developments included A.A. Polumordvinov's system using spinning Nipkow disks and filters, and Baird's demonstrations of a color system using a Nipkow disk with three spirals.
The introduction of "simultaneous" systems marked a leap forward, transmitting three primary-color signals together while maintaining compatibility with existing black-and-white receivers. RCA's system, later adopted by the NTSC, separated colors using dichroic mirrors and employed a three-electron gun receiving tube.
Digital television emerged in the late 20th century, leading to flat-screen technologies like plasma TVs and LED HDTVs, offering superior image resolution.
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colour television, the electronic delivery of sound and moving colour images produced via the transmission of sound and colour signals from a source to a receiver. The technical standards for modern colour television were first established in the middle of the 20th century. Improvements have been made continuously since that time, and in the early 21st century colour television technology changed considerably, owing particularly to advances in digital television, which largely replaced analog television technology. For more information about television technology and historical developments, see television.
Early developments
In the late 19th century Russian scientist A.A. Polumordvinov devised a system of spinning Nipkow disks and concentric cylinders with slits covered by red, green, and blue filters. But he was far ahead of the technology of the day; even the most basic black-and-white television was decades away. In 1928 John Logie Baird gave demonstrations in London of a colour system using a Nipkow disk with three spirals of 30 apertures, one spiral for each primary colour in sequence. The light source at the receiver was composed of two gas-discharge tubes, one ofmercury vapour and helium for the green and blue colours and a neon tube for red. The quality, however, was poor.
In the early 20th century many inventors designed colour systems that looked sound on paper but that required technology of the future. Their basic concept was later called the “sequential” system, which proposed to scan pictures with successive filters coloured red, blue, and green. An alternative approach—practically much more difficult, even daunting at first—would be a “simultaneous” system, which would transmit the three primary-colour signals together and which would also be compatible with existing black-and-white receivers. In 1924 Harold McCreary designed an alternative “simultaneous” system using cathode-ray tubes and a separate cathode-ray camera to scan each of the three primary-colour components of a picture. McCreary’s system failed to work as well. In 1929 Herbert Ives and colleagues atBell Laboratoriestransmitted 50-line colour television images between New York City and Washington, D.C.; this was a mechanical method, using spinning disks, but one that sent the three primary-colour signals simultaneously over three separate circuits.
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Modern colour television
AfterWorld War II the Columbia Broadcasting System (CBS; later CBS Broadcasting Inc.) began demonstrating its own sequential colour system, designed byPeter Goldmark. In 1957 the U.S. Federal Communications Commission approved CBS’s colour television and corresponding broadcast standards for immediate commercial use. However, out of 12 million television sets in existence, only some two dozen could receive the CBS colour signal, and after only a few months the broadcasts were abandoned. In June 1951 David Sarnoff, vice president and general manager of the Radio Corporation of America (RCA; later RCA Corporation), unveiled a system that used dichroic mirrors to separate the blue, red, and green components of the original image and focus each component on its own monochrome camera tube. The RCA colour system was compatible with existing black-and-white television sets.
In 1952 the U.S. National Television Systems Committee (NTSC) set a goal of creating an “industry color system.” The NTSC system that would serve into the 21st century was virtually the RCA system. The first RCA colour TV set, the CT-100, was produced in early 1954. It had a 12-inch screen and cost $1,000, as compared with current 21-inch black-and-white sets selling for $300. It was not until the 1960s that colour television became profitable. By the early 1980s, colour television sets had largely supplanted the use of black-and-white televisions.
By the first part of the 21st century, digital television, which had emerged in the late 1980s and 1990s, had rendered black-and-white and colour television sets nearly obsolete. Among the first large full-colour digital flat-screen televisions made available to consumers, in the late 1990s, were plasma televisions, which utilized liquid crystal displays. Plasma televisions were quickly replaced, however, by other technologies, such as light-emitting diode (LED) high-definition televisions (HDTVs). Such HDTVs have various advantages over traditional colour television sets, including a sleek flat-screen design and far superior image resolution.