The concept of television (distance vision) can be traced back to Galileo and his telescope. However, not until 1884, with the invention of Paul Nipkow disk Nipkow when made significant
progress to create a medium. The change would bring the television as we know it today was invented by Vladimir Zworkyn iconoscope and Philo Taylor Farnsworth. This would lead to all-
electronic television, which had a much better frame rate, higher definition picture and own lighting.
[Edit] Early developments television origins were exposed several mechanical solutions, such as the Nipkow disc in 1910, but these mechanical systems were discarded in favor of fully
electronic collection systems today.
In 1925, Scottish inventor John Logie Baird made the first real experience using two disks, one in the emitter and the receiver, who were attached to the same axis so that its rotation was
synchronous and separated by 2 mm.
The first public television broadcasts of the BBC in England conducted in 1927, and CBS and NBC in the U.S. in 1930. In both cases, mechanical systems and programs will not be issued with
a regular schedule.
The first station that regularly scheduled programming was created in 1930 in Berlin by the local branch of the National Socialist German Workers Party, but those responsible for Nazi
propaganda were not aware of the possibilities of the medium and continued to use the radio.
The emissions program started in England in 1936, and the United States on April 30, 1939, coinciding with the opening of the Fair in New York. Scheduled broadcasts were interrupted during
World War II and resumed when it ended.
[Edit] Television began broadcasting electronic 1937 regular electronic TV in France and the United Kingdom. This led to rapi d development of the television industry and a rapid increase in
viewers, but the small screen TVs were very expensive. These releases were made possible by the development of the following elements at each end of the chain: the cathode ray tube and
the iconoscope.
[Edit] Capture iconoscope imagenEl is based on the principle of photoelectric emission: the image is projected onto a mosaic of photoelectric cells that emit electrons giving rise to the image
signal. It was used in the United States between 1936 and 1946.
The vidicon tube is 2.2 cm in diameter and 13.3 cm in length based on the photoconductivity of some substances. The optical i mage is projected onto a printed circuit board which, in turn, is
explored by the other side by a very fine electron beam.
The Plumbicon is based on the same principle as the vidicon, however, the photoconductor plate is made of three layers: the first, in contact with the collector plate, and the third is formed by a
semiconductor, the second lead oxide . Thus, it creates a diode is reverse biased, as a result, the current through each unit cell in the absence of light, is extremely low and the sens itivity of
Plumbicon under these characteristics, very high.
[Edit] The main vídeoArtículo signal: Video signal
The signal transduced from the image contains the information on this, but it is necessary for restructuring, which has a perfect synchronism between the deflection and deflection scanning in
representation.
The exploration of an image is done by decomposition, first frame to frame are called lines and then reading each frame. To determine the number of frames that can be required to reconstr uct
a moving picture and the number of lines for optimal playback quality and the optimal perception of color (color TV) were conducted empirical studies and scientific the human eye and the way
they perceive. It was found that the number of frames must be at least 24 the second (later used for other reasons 25 and 30) and the number of lines must not exceed 300.
The video signal itself is composed of image information for each line (in the 625-line PAL and NTSC 525 in each box) grouped into two groups, the odd and the even lines of each frame, each
of these groups are called field lines (in the PAL system used 25 frames per second while NTSC 30). This information must be added the sync, both frame and line, that is, both vertically and
horizontally. The table being divided into two fields per frame have a vertical sync signals the beginning we are and the type of field, ie when the field begins when odd and even field starts. At
the beginning of each line is added to the sync pulse or horizontal line (with modern color TV also adds information about the timing of the color).
The image coding is between 0 V to 0.7 V for black and white. To join the sync pulse of -0.3 V, which gives a total amplitude of the video waveform of 1 V. The vertical sync consist of a series
of pulses from -0.3 V to provide information about the type of field and even times each.
The sound, audio call is treated separately in the entire production chain and is then emitted with the video in a carrier next to the charge of transporting the image.
[Edit] The development of TV
Central Control in a TV broadcasting center.
Cameras on a set of TV.Es to mid-twentieth century where the television becomes technological flag countries and each will develop their national systems and private TV. Eurovision was
created in 1953 associating several European countries connect their TV systems using microwave links. A few years later, in 1960, establishing Mundovisión that begins to make links with
geostationary satellites covering the entire world.
The television production was developed with the technical advances that allowed the recording of video and audio signals. This allowed the realization of recorded programs that could be
stored and later released. In the late 50s of the twentieth century developed the first video recorders and cameras with inte rchangeable lenses in a revolving turret in front of the picture tube.
These developments, along with developments in the machinery needed 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 which allowed the recording of the news in the field. Teams were born or ENG Electronic News. Soon after he
began to develop equipment based on the digitization of the video signal and digital signal generation, born of those developments digital effects and graphic palettes. While controlling the
assembly of machines allowed postproduction rooms that combining several elements, could perform complex programs.
The development of television did not stop the transmission of image and sound. He soon saw the a dvantage of using the channel for other services. In this philosophy was implemented in the
late 80's of XX century the teletext broadcasts news and information in text format using the free space information video signal. It also implemented enhanced sound systems, television born
stereo or dual sound and providing exceptional quality, the system that managed to succeed in the market was the NICAM.
[Edit] TV colorVéase also: Introduction of color television in different countries
NTSC
PAL, or switching to PAL
SECAM
No Information
Distribution of TV systems in the world.and in 1928, experiments were performed in the transmission of color images. In 1940, Guillermo González Camarena patented in Mexico and the U.S.,
Trichromatic System Field Sequential.
In 1948, Goldmark, based on the idea of Baird and Camarena, developed a similar system called field sequential system. The success was such that the Columbia Broadcasting System
acquired it for their TV broadcasts.
The next step was the simultaneous transmission of color images of each trinoscopio called. The trinoscopio occupied three ti mes more radio spectrum and monochromatic emissions, above,
was incompatible with them at the same time very expensive.
The high number of black and white televisions did not require that the color system was developed to be compatible with monochrome emissions. This support should take place in both
directions, emissions receptions color black and monochrome emission color reception.
In pursuit of the concept of compatibility comes luminance and chrominance. The luminance information portal brightness, light, image, corresponding to white and black, while the chrominance
carries color information. 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 able to impact small color phosphor dots, called luminophores,
using a mask, the Shadow Mask or Trimask. This allowed the tubes without trinoscópicos so bulky and cumbersome. The electron bea m impact with the luminophores emit light corresponding
primary color additive mixture generated by the original color.
While the receiver the three guns were implemented for the three primary colors in only one element in the transmitter (camera) were kept separate tubes, one for each primary color. To
separate the light is passed that makes up the image by a dichroic prism that each primary color filters to a corresponding getter.
[Edit] Current systems of TVC
EBU color bars seen in a first vectoscopio.El MFO and a 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 Hazeltime U.S. This system was adopted by the U.S. Federal C ommunication 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 us heat and is shown in monochrome receivers, and the color compone nts, the two color difference signals, the RY and BY (red
minus luminance and blue minus luminance). This double selection allows for a differentiated treatment to the color and brightness. The human eye is more sensitive to variations in brightness
and definition of the color, this makes bandwidths of both signals are different, which facilitates transmission, and both signals are due to deploy in the same band whose width is adjusted.
The NTSC system amplitude modulates two carriers of the same frequency 90 ° offset are then aggregated, QAM or quadrature. In each of the modulated carrier of the color differences, the
amplitude of the resulting signal indicates the color saturation and tint phase or tone of it. This signal is called chroma. Modulation axes are located in such a way that takes care of the fact that
the eye is most sensitive to the flesh color, this is that I axis is oriented toward the orange and the Q to the magentas. As the suppress ed carrier modulation is required to send a salute to the
same receptor generators to synchronize with it. This saves or burst is usually on the front porch of the line sync pulse. The chrominance signal is added to the luminance signal composing the
total image.
Changes in the phase of the video signal when it is transmitted dye errors, ie color (change the color of the image).
The NTSC was the base from which they started other researchers, mainly in Europe. In Germany, developed by a team led by Walter Bruch a system to correct any phase errors, this system
is PAL, Phase Altenating Line.
This phase of the subcarrier alternates in each line. Subcarrier which modulates the RY component, which is called V PAL has a 90 ° phase in a line and from 270 in t he next. This makes the
phase errors that occur in the transmission (and affecting the same and in 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 have called PAL S (PAL Simple) and if done by an electronic circuit D PAL (PAL Delay, delayed). The PAL
was proposed as pan-color system in the Oslo Conference, 1966. But no agreement was reached as a result of Western European countries, with the e xception of France, adopted PAL while
France Eastern Europe and SECAM.
In France, developed by researcher Henri de France a different system, SECAM, "Couleur SÉquentiel A Memoir" that bases its actions in the transmis sion sequence of each color component
FM modulated so that a line sends a component and the next the other component. Then the receiver combines them to deduce the color of the image.
All systems have advantages and disadvantages. While the NTSC and PAL difficult editing the video signal by color sequence in four and eight fields, respectively, the system made it
impossible to work SECAM mixing video signals.
[Edit] High definition "HD" Main article: HDTV
The system of standard definition television, known by the initials "SD", has, in PAL, a definition of 720x576 pixels (720 horizontal dots per line and 576 vertical dots corresponding to the active
lines of PAL) this makes a PAL image has a total of 414,720 pixels. In NSTC points are kept online, but the number of active lines is only 525 making a total of 388,800 pixels pixels being
slightly wider at slightly higher in PAL and NSTC.
They have developed 28 different systems of HDTV. There are differences in terms of pictures, number of lines and pixels and a bar. They can be grouped into four main groups of which two
have already become obsolete (those relating to the rules of the SMPTE 295M, 240M and 260M) remaining two differ mainly in the number of active lines, one of 1080 active lines (SMTP
274M) and one of 720 active lines (SMTP 269M).
In the first group, with 1,080 active lines, there are differences in frame rate and number of samples per line (although the number of samples per line uptime remains at 1,920) as well as
sweeping changes, there is progressive scan or interlaced. Just as occurs in the second group, which are 720 active lines having 1280 samples per active line time. In this case the shape is
always progressive scanning.
In the system of HD of 1,080 lines and 1,920 samples per line we have 2,073,600 pixels in the image and the HD system of 720 lines and 1,280 lines we have 921,600 samples per pixel on the
screen. In relation to conventional systems have the resolution of 1,080 lines system is 5 times greater than that of PAL-five and a half times that of NTSC. HD system with 720 lines is 50%
higher than in PAL and 66% higher than NTSC. [1]
The high resolution also calls for a redefinition of changing the color space gamut triangle.
[Edit] The aspect ratio
Negro.En old and white TV's 90's of the twentieth century began to develop systems for HDTV. All these systems, in principle analog, increased the number of lines in the image and change
the aspect ratio from the format used previously, aspect ratio 4 / 3, a landscape format for 16 / 9. This new format, more pleasing to the eye was established as a standard even in standard
definition broadcasts.
The aspect ratio is expressed by the width of the screen in relation to height. The standard format until then had an aspect ratio of 4 / 3. The adoptee is 16 / 9. The compatibility between the two
aspect ratios can be done in different ways.
An image of 4 / 3 that will be viewed on a screen 16 / 9 can be presented in three different ways:
Vertical black bars on either side (pillarbox). Keeping the ratio of 4 / 3 but losing part of the active display area.
Enlarging the image until it fills the screen horizontally. You lose part of the image at the top and bottom of it.
Deforming the image to fit the format of the screen. It uses the entire screen and can see the whole picture, but with altered geometry (circles are ellipses with the major diameter oriented from
right to left).
An image of 16 / 9 to go see on a screen of 4 / 3, similarly, has seen three ways:
With horizontal bars above and below the picture (letterbox). You see the whole picture but lose screen size (there are several letterbox formats depending on the visible part of the image you
see (the bigger it becomes more cuts), we use the 13 / 9 and 14 / 9 ).
Enlarging the image to fill the screen vertically, losing the sides of the image.
Deforming the image to fit the aspect ratio of the screen. You see the whole image across the screen, but with altered geometry (circles are ellipses with the major diameter oriented from top to
bottom). [1]
[Edit] The main PALplusArtículo: PALplus
In Western Europe, where the television system of most countries is the PAL was developed with support from the European Union, a format somewhere between high definition and standard
definition. This format was called PALplus and although it was supported by the administration failed to materialize.
The PALplus was an extension of PAL to transmit images of 16 / 9 without losing vertical resolution. In a normal TV receiving a landscape image with black bars above and below it (letterbox)
of 432 active lines. The PALplus sent additional information to fill the black stripes coming to 576 lines of vertical resolution. Using auxiliary signals that were on the lines of vertical sync interval
command of the receiver indicating whether the feedback PALplus had been made in progressive scan or interlaced. The system was extended with the so-called "Colorplus" it improved color
decoding.
[Edit] The digitization
Digital Terrestrial Television in the world. 80 late twentieth century began to develop scanning systems. The television scanning has two distinct parts. On one side is the digitization of
production and the other the transmission.
As production developed several digitizing systems. The first of them were based on digitizing composite video signal unsuccessful. The approach of the components of the digitized video
signal, ie the luminance and color differences, was what was most appropriate. It was initially developed signal systems in parallel, with thick cables that needed a thread for each bit, soon
replaced the multiplexed transmission cable in time for words corresponding to each of the components of the signal as well This system allowed include audio, embedded in the information
provided, and a number of utilities.
To maintain the quality needed for the production of TV Quality developed the standard CCIR-601 Study. While it allowed the development of other less demanding standards for the field of
light production (EFP) and electronic news gathering (ENG).
The difference between the two fields, the production quality of study and ENG as lies in the magnitude of the bit stream generated by digitizing the signals.
Reducing the bit stream digital video signal resulted in a series of algorithms, all based on discrete cosine transform in both spatial domain and in the storm, that reduced the flow enabling the
construction of more affordable equipment . This allowed them access to small production companies and TV broadcast giving rise to the rise of local television.
As for transmission, scanning the same was made possible by compression techniques able to reduce the flow to less than 5 Mbit / s, we must remember that the original flow of a studio quality
signal has 270 Mbit / s. This compression is called MPEG-2 streams produced between 4 and 6 Mbit / s without appreciable loss of subjective quality.
Digital TV transmissions have three main areas depending on the shape of the same even when they are similar in terms of technology. Transmission is by satellite, terrestrial cable and
satellite radio, this is known as DTT.
The advance of computer technology, both hardware and software, led to production systems based on computer processing of the television signal. Storage systems such as VCRs, became
replaced by video and computer servers to store files passed their information on hard disks and data tapes. Video files are metadata include information about your content. Access to
information is from the computers themselves where they are video editing programs so that the information residing in the fi le is accessible in real time by the user. Actually the files are
structured in three levels, online, for that very frequent usage information that resides on hard disk drives, the near line, frequently used information that resides on data tapes and they are in
large automated libraries and the deep archive where the information is online and requires manual joining the system. All this is controlled by a database where are the seats of the information
resident in the system.
The incorporation of information system via the so-called function of intake. The sources can be generated and formats are converted by computer or video converter to computer files. The
deposits made in the field for ENG or EFP equipment are recorded in formats compatible with the storage using different media to magnetic tape, existing technologies are blue ray DVD
(Sony), recording in RAM (Panasonic) and hard disk recording (Ikegami).
The existence of the video server enables the automation of releases and news programs by making lists of emission, the so-called play-out