Television

Television, TV and popular TV, is a telecommunication system for latransmisión and receiving moving pictures and sound at a distance.
This transmission can be carried by radio waves or by specialized networks of cable television. The receiver of the signals is the TV.
The word "television" is a hybrid of the Greek word "Tele" (distance) and the Latin "visio" (vision). TV The term refers to all aspects of television broadcasting and programming. It is sometimes abbreviated as TV. This term was first used in 1900 by Constantin Perski at the International Congress of Electricity in Paris.
The World Television Day is celebrated on November 21 in commemoration of the date it was held in 1996 the first World Television Forum at the United Nations.
The first attempts to transmit remote images are made by electricity and mechanical systems. The electricity was a means of union between the points and was used to perform
collection and receipt of the image, the mechanical means of movement carried out the tasks to perform sequential scans and decomposition of the image to convey. By 1884 came the first transmission systems drawings, maps, writings and photographs called telephoto. In these first devices used the difference in resistance for uptake.
The development of selenium photocells, in which the resistivity varies by light falling on them, the system is perfected to the point where in 1926 he established a regular service telephoto transmission between London and New York. Radio waves soon replaced the copper cables, although they never completely eliminate, especially in point to point services.
Telephoto development reached its peak with teleinscriptores, and its transmission system. These devices allowed to receive the daily newspaper at the customer, by printing the same as that from a transmitter to specialized.
Until the early 80's came the twentieth century using telephoto systems for
transmission of photographs for the media.
The moving image is the hallmark of the television. The first developments of the French made Rionoux and Fournier in 1906. They developed an array of photosensitive cells that connected, the first one by one, with another array of bulbs. Each cell
the issuer accounted for a lamp into the receiver.
Many were soon replaced by a single pair cables. For this purpose, a switching system that would put every cell in every moment in contact with each
lamp. The problem was the timing of both switches and the speed at which had to rotate to achieve a complete picture that was seen by the eye as such.
The need to send the image information in series, ie using only one way as in the case of the photosensitive matrix, quickly accepted. Then it developed navigation systems, also called disintegration of the image. Developed mechanical and electrical systems.
In 1884 Paul Nipkow designed and patented the so-called Nipkow disk, a television project that could not be implemented. In 1910, the Nipkow disk was used in developing television systems of the early twentieth century and in 1925, 25 March, the Scottish inventor John Logie Baird made the first real experience using two disks, one in emitter and the receiver, which were attached to the same axis to dummy with a definition of 28 lines and a frame rate of 14 frames per second.
Baird gave the first public demonstration of the operation of a television system to members of the Royal Institution and a reporter on January 26, 1926 at his laboratory in London. In 1927, Baird transmitted a signal to 438 miles through a telephone line between London and Glasgow.
This disk allows the realization of a sequential scan of the image through a series of holes drilled in it. Each hole, which in theory should have an infinitesimal size and the practice was 1mm, sweeping a line of the image and how these, holes were slightly off, ended up doing the clean sweep of it. The number of lines that were taken was 30 but this did not produce the desired results, the image quality was unsatisfactory.
In 1928 he founded the company Baird Baird TV Development Co to commercially exploit the TV. The company won the first transatlantic television signal from London to New York. That same year Paul Nipkow seen in the Berlin Radio Exhibition TV system working perfectly based on his invention with his name at the bottom of it. In 1929, begin regular broadcasts in London and Berlin based on Baird Nipkow system and middle band was broadcast on radio.
Other browsers were developed that made mechanical and Telefunken house, which gave good results, but it was very complex and consisted of a cylinder with holes having a lens every one of them.
The formation of the image at the reception was done by the same principle as used in the collection. Another similar disc, rotating synchronously, was used to look through it a neon lamp whose brightness correspond to the light received at that point
image. This system, by the tiny size of the training area of the image, not very successful because it allowed only be seen by a person, even when trying to enlarge the image by using lenses. Based systems were developed
tape rather than disk, and also developed, which was what he managed to solve the problem of the size of the image, a mirror system mounted on a drum that did the presentation on a screen. For this, the drum had the mirrors slightly tilted, placed
helically. This drum is known as the wheel Weiller. For the practical development of these sets was necessary to replace the neon lamp, the light was not
enough, by other methods, and among them was used to put a gas discharge lamp and the light passing it by a Kerr cell which regulated the flow of light in relation to the tension applied to it in their terminal . The full system development was achieved with the use of the tone wheel to perform the synchronization between the transmitter and receiver.
The exploration of the image, which had developed progressively by the experiences and Nipkow Senlecq questioned by exposure of the principle of interlaced scanning
developed by Belin and Toulon. Interlaced scanning solve the problem of image persistence, the first line drawn is lost when they had not yet traced the latest
producing the effect known as wave. In interlaced scanning lines are scanned first and then odd pairs and performs the same in the presentation of the image. Brillounin
Nipkow disk perfected to perform interlaced scanning by placing a lens in the hole attracted increasing brightness.
In 1932 the first broadcasts are made in Paris. These emissions have a definition of 60 lines but three years later would be emitting at 180. The precariousness of the cells was used to capture that very intense light should produce very hot scenes that prevented the development of work on the sets.
The phonic wheel was the mechanical timing system gave better results. It consisted of an iron wheel that had so many teeth and had holes in the drum or disk. The wheel and were united by the same route. The wheel was in the middle of two coils were crossed by the signal coming from the issuer. The broadcast center was given at the beginning of each hole, the beginning of each line, a pulse much more intense and comprehensive changes
grabber normal cells, when it was received at the receiver by passing through the coils causes the wheel to step corresponding positioning hole.
In 1937 began regular broadcasts of electronic TV in France and the United Kingdom. This led to rapid development of the television industry and a rapid increase in viewers while the small-screen televisions were very expensive. These releases were made possible by the development of the following items at each end of the chain.
The implementation of so-called cathode ray tube or pipe Braum, S. Thomson in 1895, was a precedent that would be of great significance in television, but failed to integrate, due to technological deficiencies, even into the twentieth century and continues in the first half of the century.
Since the early experiments on cathode rays until the tube is sufficiently developed for use in television took many steps in this research. The
Wehnelt research, adding his cylinder, the improvements of the controls
electrostatic and electromagnetic beam, with the development of so-called "electronic lens" of Vichert and deflection systems allowed the researcher Holweck
developed the first Braum tube intended for television. For this system to work properly we had to build a particular issuer, the issuer was made Belin which was based on a moving mirror and a mechanical system for the sweep.
After solving the problem of image display in the reception was to address the uptake in the issuer. Mechanical explorers slowed down the progress of the art TV.
It was evident that progress must come from the hand of electronics, as in the case of the reception. On January 27, 1926 John Logie Baird gave a demonstration before the Royal Institution of England, the sensor was mechanical, consisting of three albums and very construction
rudimentary. Alfredo Dinsdale describes it this way in his book Television;
The first image on a cathode ray tube formed in 1911 in the Technological Institute of St. Petersburg and was a white stripe on black background and were obtained by Boris Rosing in collaboration with Zworrykin. The recruitment was done by two mirrors drums (Weiller system) and generated a 30-line interlaced scanning and 12.5 frames per second.
Timing signals were generated by potentiometers attached to the drum of mirrors that applied to the coils deflexoras the CRT beam whose intensity was proportional to the light receiving photoelectric cell.
In 1931, Vladimir Kosma Zworykin developed the electronic capturing both expected, iconoscope. This electronic tube allowed the abandonment of all other systems were being used and lasted, with modifications, until the advent of CCD's sensors late twentieth century.
The iconoscope is based on an electronic mosaic composed by thousands of small independent photocells were created by the construction of a sandwich of three layers,
a very thin mica was coated on one side of a conductive substance (graphite fine powder or silver) and on the other side a photosensitive substance composed of thousands of small globular silver and cesium oxide. This mosaic, which was also known as electronic mosaic Zworykin was placed inside a vacuum tube and it was projected by a lens system, image capture. The reading of "electronic image" generated in the mosaic was made with an electron beam provided small capacitors photoelectric electrons necessary for neutralization. To this end, projects a beam of electrons on the mosaic, the currents generated in each discharge, proportional to
load of each cell and this in intensity of light from that point of the image passed to the amplifier circuits and thence to the transmission chain, after the various processes required for the optimum performance of the TV system.
Exploring the mosaic of the electron beam is made by an electromagnetic deflection system, like that used in the receiver tube.
It also developed other camera tubes as the image dissector Philo Taylor Farnsworth
and then the superemitrón Icotrón and that was a hybrid of iconoscope and dissector, and finally appeared orticón, developed by RCA and the house was much smaller in size, the iconoscope and more sensitive. This tube was developed and which lasted until his death.
Vladimir Zworykin completed his studies and experiments in the RCA iconoscope after leaving St. Petersburg and working with Philo Taylor Farnsworth who accused him of copying his work on
the image dissector.
Designed transducers were the basis for the television cameras. These teams were involved, and integrate everything needed to capture an image and transform it into an electrical signal. The signal, which contains the information image pulses necessary for the synchronization of the receivers, called the video signal. Once the signal has occurred, it can be manipulated in various ways, to its broadcast by the antenna, the desired delivery system.
The signal transduced from the image contains the information on this, but as we have seen, is necessary for reorganization, which has a perfect synchronism between the scanning deflection and the deflection in the representation.
The exploration of an image is accomplished by decomposition, first frames which are called frames and then in line, reading each frame. To determine the number of
tables can be necessary to reconstruct a moving image and the number of lines for optimum quality reproduction and optimal color perception (on TV in color) were conducted and scientific empirical studies of the human eye and way of perceiving. It was found that the number of frames must be at least 24 from the second (later used for other reasons 25 and 30) and the number of lines must be above 300.
The video signal itself is composed of image information corresponding to each line (in the 625-line PAL and NTSC 525 per table) clustered into two groups, the odd and the even lines of each field, each one of these groups of lines are
called a field (in the PAL system used 25 frames per second while NTSC 30). This information must be added the synchronism of both box and line, that is, both vertically and horizontally. Table being divided into two fields for each frame have a vertical sync signals the beginning that we and the field type is
that when the odd field begins and when the par begins. At the beginning of each line is added to the line sync pulse or horizontal (with modern color TV also adds information on the timing of the color).
The image coding is between 0 V to 0.7 V for black and white. To join the sync pulses of -0.3 V, giving a total range of the video waveform 1V. The vertical sync are made of a series of pulses of -0.3 V to provide information about the type of field and even the times of each one of them.
Sound, audio call is treated separately in the whole chain of production and then next to the video is broadcast in a carrier next to the charge of transporting the image.
In 1945 he established the rules governing the exploration CCIR, modulation and transmission of TV signal. There were many systems that have very different resolutions, from 400 lines to over 1,000. This produced different bandwidths in the transitions. Little by little they were focusing on two systems, the 512 lines, adopted by the U.S. and 625 line adopted by Europe (Spain took the 625 lines in 1951). Also was an early adopter format 4 / 3 for the aspect ratio of the image.
In the mid twentieth century where the TV becomes the country's technological flag and each will develop their systems of national and private TV. In 1953, Eurovision is created that links to several countries in Europe connecting their TV systems using microwave links. A few years later, in 1960, establishing Mundovisión beginning to make links with geostationary satellites covering the whole world.
Television production was developed with technical advances that allowed the recording of video and audio signals. This allowed the implementation of programs that could be recorded
stored and later released. In the late 50's of XX century they developed the first video recorders and cameras with interchangeable lenses in a turret that turned in front of the picture tube. These developments, along with the development of the necessary machines for mixing and electronic generation from other sources, allowed a very high development of production.
In the 70 zoom lenses were introduced and began to develop smaller recorders allow recording of the news in the field. Were born or ENG electronic news gathering equipment. Soon after he began to develop computers based on
digitization of the video signal and digital signal generation, born of those developments digital effects and graphic pallets. While the control of machines allowed
installation of post-production facilities, by combining several elements, could perform complex programs.
The development of television did not stop the transmission of image and sound. He soon saw the advantage of using the channel to provide other services. This philosophy was implemented in the late
80 years of the twentieth century teletext broadcast news and information in text format using the free space information from the video signal. Also implemented improved sound systems, television born in stereo or dual sound and providing the exceptional quality, the system managed to prevail in the market was the NICAM.
In 1928, experiments were performed in the transmission of color images.
Baird, based on the trichromatic theory of Young, experimented with the Nipkow disks that covered the holes with red filters, green and blue making the first images broadcast in color on 3 July 1928. On August 17, 1940 Guillermo González Camarena patented in the U.S. and Mexico, a Field Sequential System Trichromatic. Eight years later, 1948, Goldmark, based on the idea of Baird and Camarena, developed a similar system, called field sequential system which consisted of a series of filters of red,
green and blue that turn overriding the sensor and, similarly, in the receiver, take precedence over the image formed on the screen of cathode ray tube. The success was such that the Columbia Broadcasting System purchase for their TV broadcasts.
The next step was the simultaneous transmission of images of each color with the so-called trinoscopio.
The trinoscopio occupied three times more radio spectrum and monochromatic emissions, above, was incompatible with them at the same time very expensive.
The high number of black and white TV demanded that the color system was developed to be compatible with monochrome emissions. This support should take place in both directions, color emission receptions in black and white monochrome emission color receptions.
In search of compatibility born the concept of luminance and chrominance. The luminance carries the brightness information, light, image, corresponding to black and white, while the chrominance color information portal. These concepts were presented by Valensi in 1937.
In 1950 the Radio Corporation of America (RCA) develops a picture tube that carries three electron guns, the three beams were capable of hitting small colored phosphor dots, called luminophores, using a mask, the Shadow Mask or Trimask. This allowed the tubes without trinoscópicos so bulky and cumbersome. The electron beam upon impact with the luminophores emitting light of the corresponding primary color by additive mixture generates the original color.
While the receiver the three guns were implemented for the three primary colors in a single element, the issuer, the camera kept separate tubes, one for each primary color. For the separation is passed the light that makes up the image by a dichroic prism which filters each primary color to its corresponding sensor.
The first color television system developed respecting the dual compatibility with monochrome television was developed in 1951 by a group of engineers led by Hirsh in the laboratories of the Corporation in the U.S. Hazeltime This system was adopted by the U.S. Federal Communication Commission (FCC) and was the NTSC stands for National Television System Commission. The system was successful and spread throughout North America and Japan.
The basic signals used are the luminance (Y), which gives brightness and is shown in monochrome receivers, and the components of color, two color difference signals, the RY and BY (red minus luminance and blue minus luminance). This double selection allows a different approach to color and brightness. The human eye is more sensitive to variations of brightness and definition to color, this makes the bandwidths of both signals are different, which facilitates the transmission and both signals should be implemented in the same band whose width is adjusted.
NTSC amplitude modulated on two carriers of the same frequency shifted 90 º which is then added, QAM or quadrature modulation. In each of the carriers is modulated one of the color differences, the amplitude of the resulting signal indicates the color saturation and tint or tone phase of it. This signal is called chroma. Modulation axes are positioned so that takes care of the fact that the eye is more sensitive to color flesh, this is the first axis is oriented towards the orange and magenta Q towards. As the modulation with suppressed carrier is needed to send a volley of it for generators to the receiver to synchronize with it. This saves or burst is usually on the front porch of the sync pulse line. The chroma signal is added to the luminance signal composing the entire picture.
Changes in the phase of the video signal when it is transmitted errors of dye, ie color (change the color of the image).
The NTSC was the basis of which left other researchers, mainly in Europe. In Germany was developed by a team led by Walter Bruch a system to correct any phase r, this system is the PAL, Phase Altenating Line.
For this phase of the subcarrier is Altena on each line. The subcarrier that modulates the component RY, that PAL is called V, has a 90 ° phase in a line and from 270 in the next, this means that phase errors that occur in the transmission (and affecting the same and the same direction on both lines) are compensated for the representation of the image to see a line next to each other, if the integration of image for color correction is undertaken by the human eye we called PAL S (Single PAL) and if done by an electronic circuit D PAL (PAL Delay, delayed). The PAL was proposed as a pan-European system of color in the Oslo Conference in 1966 but no agreement was reached as a result of Western European countries, with the exception of France, adopted the PAL while Eastern Europe and France SECAM.
In France developed by the researcher Henri de France a different system, SECAM, "SÉquentiel Couleur À Mémoire" whose work is based on the sequential transmission of each color component FM modulated so that a line sends a component and the next the other component. The receiver will combine to deduce the color of the image.

All systems have advantages and disadvantages. While the NTSC and PAL difficult editing the video signal by the sequence of color in four and eight fields, respectively, the SECAM system made it impossible to work mixing video signals.
• 1884 - The German student Paul Nipkow designed and patented what is considered as the first television history: the Nipkow disk.
• 1897 - Karl Ferdinand Braun built the first cathode ray tube.
• 1900 - Perskyi coined the word "television" at the Exposition Universelle in Paris.
• 1907 - Nipkow's design can be done.
• 1911 - Rosing and Zworykin created a television system with images and not moving very raw.
• 1923 - Vladimir Zworykin iconoscope develops the first practical camera tube.
• 1926 - The Japanese Kenjito Takayanagi made the first transmission of television using a cathode ray tube.
• 1927 -
Philo Farnsworth in San Francisco made the first public demonstration of his image dissector, a system similar to iconoscope.
• 1927 - John Logie Baird transmits a signal 438 miles through a telephone line between London and Glasgow.
• 1928 - Baird Television Development Company achieved the first transatlantic television signal from London to New York.
• 1929 - BBC transmits images of 30 lines formed mechanically.
• 1932 - Sold in England 10,000 television receivers with 30 lines Nipkow disk.
• 1937 - Marconi-EMI sold a 405-line all-electric.
• 1941 - Guillermo González Camarena
- Engineer of Mexican origin obtained on August 14 in U.S. patent 2,296,019 for inventing a simplified cromoscópico adapter for television (a first version was created by John Logie Baird in 29, but not being operational, and being perfected by him before his death in 1946), no doubt, among the many projects in color television, one of the fathers of this was Camarena. [1] [2]
• 1956 - The U.S. House AMPEX designed the first VCR, the quadruplex.
• 1985 - Sony develops Betacam recording system. Ampex Ampex ADO developed the first Digital Optical digital effects.
• 1980 1982 - Development of standards converters and digital chroma-keys.
• 1983 - pass the CCIR-601 standard, and studio quality 4:2:2 to 4:1:1 and 4:2:0 for ENG.
• 1985 - First D1 format digital video recorders by Ampex and Sony. Develop digital effects (DVE).
• 1987 - Sale parallel interface standard for connecting digital devices.
• 1987 - 1992 - Creation D2 and D3 formats that digitize the composite video signal. Formats were transit.
• 1993 - adopted the standard for the series connection of equipment, called SDI Serial Digital Interface. Sale Panasonic D5 system and Sony Digital Betacam.
• 1995 -
Approving the regulations for digital broadcasting, satellite DVB-S, cable DVB-C based on MPEG-2 compression.
• 1997 -
Born digital satellite platforms. Adopting the DVB-T standard for digital terrestrial television. In the U.S. adopting the ATSC (Advanced Television System Committee) for the transmission of digital terrestrial television.