   #copyright

Television

2007 Schools Wikipedia Selection. Related subjects: Engineering; Television

   Braun HF 1, Germany, 1958
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   Braun HF 1, Germany, 1958
   OT-1471 Belweder, Poland, 1957 1. power switch / volume 2. brightness
   3. pitch 4. vertical synchro 5. horizontal synchro 6. contrast 7.
   channel tuning 8. channel switch
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   OT-1471 Belweder, Poland, 1957
   1. power switch / volume
   2. brightness
   3. pitch
   4. vertical synchro
                           5. horizontal synchro
                           6. contrast
                           7. channel tuning
                           8. channel switch

   Television is a telecommunication system for broadcasting and receiving
   moving pictures and sound over a distance. The term has come to refer
   to all the aspects of television from the television set to the
   programming and transmission. The word is derived from mixed Latin and
   Greek roots, meaning "far sight": Greek τῆλε "tele", far, and Latin
   visio-n, sight (from video, vis- to see).

History

   The television was not invented by a single person, but by a number of
   scientists' advancements contributing to the ultimate all-electronic
   version of the invention. The origins of what would become today's
   television system can be traced back as far as the discovery of the
   photoconductivity of the element selenium by Willoughby Smith in 1873
   followed by the work on the telectroscope and the invention of the
   scanning disk by Paul Nipkow in 1884. All practical television systems
   use the fundamental idea of scanning an image to produce a time series
   signal representation. That representation is then transmitted to a
   device to reverse the scanning process. The final device, the
   television (or T.V. set), relies on the human eye to integrate the
   result into a coherent image.
   A transistor-based portable television, typical of NTSC models of the
   late 1960s and 1970s
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   A transistor-based portable television, typical of NTSC models of the
   late 1960s and 1970s

   Electromechanical techniques were developed from the 1900s into the
   1920s, progressing from the transmission of still photographs, to live
   still duotone images, to moving duotone or silhouette images, with each
   step increasing the sensitivity and speed of the scanning photoelectric
   cell. John Logie Baird gave the world's first public demonstration of a
   working television system that transmitted live moving images with tone
   graduation (grayscale) on 26 January 1926 at his laboratory in London,
   and built a complete experimental broadcast system around his
   technology. Baird further demonstrated the world's first colour
   television transmission on 3 July 1928. Other prominent developers of
   mechanical television included Charles Francis Jenkins, who
   demonstrated a primitive television system in 1923, Frank Conrad who
   demonstrated a movie-film-to-television converter at Westinghouse in
   1928, and Frank Gray and Herbert E. Ives at Bell Labs who demonstrated
   wired long-distance television in 1927 and two-way television in 1930.
   1950s television set
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   1950s television set

   Colour television systems were invented and patented even before
   black-and-white television was working; see History of television for
   details.

   Completely electronic television systems relied on the inventions of
   Philo Taylor Farnsworth, Vladimir Zworykin and others to produce a
   system suitable for mass distribution of television programming.
   Farnsworth gave the world's first public demonstration of an
   all-electronic television system at the Franklin Institute in
   Philadelphia on 25 August 1934.

   Regular broadcast programming occurred in the United States, the United
   Kingdom, Germany, France, and the Soviet Union before World War II. The
   first regular television broadcasts with a modern level of definition
   (240 or more lines) were made in England in 1936, soon upgraded to the
   so-called "System A" with 405 lines. Regular network broadcasting began
   in the United States in 1946, and television became common in American
   homes by the middle 1950s. While North American over-the-air
   broadcasting was originally free of direct marginal cost to the
   consumer (i.e., cost in excess of acquisition and upkeep of the
   hardware) and broadcasters were compensated primarily by receipt of
   advertising revenue, increasingly United States television consumers
   obtain their programming by subscription to cable television systems or
   direct-to-home satellite transmissions. In the United Kingdom, France,
   and most of the rest of Europe, on the other hand, operators of
   television equipment must pay an annual license fee, which is usually
   used to fund (wholely or partly) the appropriate national public
   service broadcaster/s (e.g. British Broadcasting Corporation, France
   Télévisions, etc.).
   Digital video equipment in a cutting room
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   Digital video equipment in a cutting room

Technology

Elements of a television set

   The elements of a simple television system are:
     * An image source - this may be a camera for live pick-up of images
       or a flying spot scanner for transmission of films
     * A sound source.
     * A transmitter, which modulates one or more television signals with
       both picture and sound information for transmission.
     * A receiver (television) which recovers the picture and sound
       signals from the television broadcast.
     * A display device, which turns the electrical signals into visible
       light.
     * A sound device, which turns electrical signals into sound waves to
       go along with the picture.

   Samsung LE26R41BD HDTV
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   Samsung LE26R41BD HDTV

   Practical television systems include equipment for selecting different
   image sources, mixing images from several sources at once, insertion of
   pre-recorded video signals, synchronizing signals from many sources,
   and direct image generation by computer for such purposes as station
   identification. Transmission may be over the air from land-based
   transmitters, over metal or optical cables, or by radio from
   synchronous satellites. Digital systems may be inserted anywhere in the
   chain to provide better image transmission quality, reduction in
   transmission bandwidth, special effects, or security of transmission
   from reception by non-subscribers.

Display technology

   Thanks to advances in display technology, there are now several kinds
   of video displays used in modern TV sets:
     * CRT(Cathode Ray Tube): The most common displays are direct-view
       CRTs for up to 40 in (100 cm) (in 4:3) and 46 in (115 cm) (in 16:9)
       diagonally. These are still the least expensive, and are a refined
       technology that can still provide the best overall picture quality.
       As they do not have a fixed native resolution, in some cases they
       are also capable of displaying sources with a variety of different
       resolutions at the best possible image quality. The frame rate or
       refresh rate of a typical NTSC format CRT TV is 60 Hz, and for the
       PAL format, it is 50 Hz. A typical NTSC broadcast signal's visible
       portion has an equivalent resolution of about 640x480 pixels. It
       actually could be slightly higher than that, but the Vertical
       Blanking Interval, or VBI, allows other signals to be carried along
       with the broadcast.

   Enlarge
     * Rear projection: Most very large screen TVs (up to over 100 inch
       (254 cm)) use projection technology. Three types of projection
       systems are used in projection TVs: CRT-based, LCD-based, and DLP
       (reflective micromirror chip) -based. Projection television has
       been commercially available since the 1970s, but at that time could
       not match the image sharpness of the CRT; current models are vastly
       improved, and offer a cost-effective large-screen display.
          + A variation is a video projector, using similar technology,
            which projects onto a screen.
     * Flat panel (LCD or plasma): Modern advances have brought flat
       panels to TV that use active matrix LCD or plasma display
       technology. Flat panel LCDs and plasma displays are as little as 1
       inch thick and can be hung on a wall like a picture or put over a
       pedestal. Some models can also be used as computer monitors.
     * LED technology has become one of the choices for outdoor video and
       stadium uses, since the advent of ultra high brightness LEDs and
       driver circuits. LEDs enable scalable ultra-large flat panel video
       displays that other existing technologies may never be able to
       match in performance.

   Each has its pros and cons. Flat panel LCD display can have narrow
   viewing angles and so may not suit a home environment. Rear projection
   screens do not perform well in natural daylight or well lit rooms and
   so are best suited to dark viewing areas. A complete run down of the
   pros and cons of each display should be sought before purchasing a
   single television technology.

Terminology for televisions

   Pixel resolution is the amount of individual points known as pixels on
   a given screen. A typical resolution of 720x480 means that the
   television display has 720 pixels across and 480 pixels on the vertical
   axis. The higher the resolution on a specified display the sharper the
   image. Contrast ratio is a measurement of the range between the
   brightest and darkest points on the screen. The higher the contrast
   ratio, the better looking picture there is in terms of richness,
   deepness, and shadow detail.

   The brightness of a picture measures how vibrant and impacting the
   colours are. Measured in cd / m^2 equivalent to the amount of candles
   required to power the image.

Transmission band

   There are various bands on which televisions operate depending upon the
   country. The VHF and UHF signals in bands III to V are generally used.
   Lower frequencies do not have enough bandwidth available for
   television. Although the BBC initially used Band I VHF at 45 MHz, this
   frequency is no longer in use for this purpose. Band II is used for FM
   radio transmissions. Higher frequencies behave more like light and do
   not penetrate buildings or travel around obstructions well enough to be
   used in a conventional broadcast TV system, so they are generally only
   used for satellite broadcasting, which uses frequencies around 10 GHz.
   TV systems in most countries relay the video as an AM (
   amplitude-modulation) signal and the sound as a FM (
   frequency-modulation) signal. An exception is France, where the sound
   is AM.

Aspect ratios

   Aspect ratio refers to the ratio of the horizontal to vertical
   measurements of a television's picture. Mechanically scanned television
   as first demonstrated by John Logie Baird in 1926 used a 7:3 vertical
   aspect ratio, oriented for the head and shoulders of a single person in
   close-up.

   Most of the early electronic TV systems from the mid-1930s onward
   shared the same aspect ratio of 4:3 which was chosen to match the
   Academy Ratio used in cinema films at the time. This ratio was also
   square enough to be conveniently viewed on round cathode-ray tubes
   (CRTs), which were all that could be produced given the manufacturing
   technology of the time. (Today's CRT technology allows the manufacture
   of much wider tubes, and the flat-screen technologies which are
   becoming steadily more popular have no technical aspect ratio
   limitations at all.) The BBC's television service used a more squarish
   5:4 ratio from 1936 to 3 April 1950, when it too switched to a 4:3
   ratio. This did not present significant problems, as most sets at the
   time used round tubes which were easily adjusted to the 4:3 ratio when
   the transmissions changed.

   In the 1950s, movie studios moved towards widescreen aspect ratios such
   as CinemaScope in an effort to distance their product from television.
   Although this was initially just a gimmick, widescreen is still the
   format of choice today and square aspect ratio movies are rare. Some
   people argue that widescreen is actually a disadvantage when showing
   objects that are tall instead of panoramic, others say that natural
   vision is more panoramic than tall, and therefore widescreen is easier
   on the eye.

   The switch to digital television systems has been used as an
   opportunity to change the standard television picture format from the
   old ratio of 4:3 (1.33:1) to an aspect ratio of 16:9 (approximately
   1.78:1). This enables TV to get closer to the aspect ratio of modern
   widescreen movies, which range from 1.66:1 through 1.85:1 to 2.35:1.
   There are two methods for transporting widescreen content, the better
   of which uses what is called anamorphic widescreen format. This format
   is very similar to the technique used to fit a widescreen movie frame
   inside a 1.33:1 35mm film frame. The image is compressed horizontally
   when recorded, then expanded again when played back. The anamorphic
   widescreen 16:9 format was first introduced via European PALPlus
   television broadcasts and then later on "widescreen" DVDs; the ATSC
   HDTV system uses straight widescreen format, no horizontal compression
   or expansion is used.

   Recently "widescreen" has spread from television to computing where
   both desktop and laptop computers are commonly equipped with widescreen
   displays. There are some complaints about distortions of movie picture
   ratio due to some DVD playback software not taking account of aspect
   ratios; but this may subside as the DVD playback software matures.
   Furthermore, computer and laptop widescreen displays are in the 16:10
   aspect ratio both physically in size and in pixel counts, and not in
   16:9 of consumer televisions, leading to further complexity. This was a
   result of widescreen computer display engineers' uninformed assumption
   that people viewing 16:9 content on their computer would prefer that an
   area of the screen be reserved for playback controls, subtitles or
   their Taskbar, as opposed to viewing content full-screen.

Aspect ratio incompatibility

   The television industry's changing of aspect ratios is not without
   difficulties, and can present a considerable problem.

   Displaying a widescreen aspect (rectangular) image on a conventional
   aspect (square or 4:3) display can be shown:
     * in " letterbox" format, with black horizontal bars at the top and
       bottom
     * with part of the image being cropped, usually the extreme left and
       right of the image being cut off (or in " pan and scan", parts
       selected by an operator)
     * with the image horizontally compressed

   A conventional aspect (square or 4:3) image on a widescreen aspect
   (rectangular with longer horizon) display can be shown:
     * in " pillar box" format, with black vertical bars to the left and
       right
     * with upper and lower portions of the image cut off (or in "tilt and
       scan", parts selected by an operator)
     * with the image horizontally distorted

   A common compromise is to shoot or create material at an aspect ratio
   of 14:9, and to lose some image at each side for 4:3 presentation, and
   some image at top and bottom for 16:9 presentation. In recent years,
   the cinematographic process known as Super 35 (championed by James
   Cameron) has been used to film a number of major movies such as
   Titanic, Legally Blonde, Austin Powers, and Crouching Tiger, Hidden
   Dragon (see also: List of top-grossing films shot in Super 35). This
   process results in a camera-negative which can then be used to create
   both wide-screen theatrical prints, and standard " full screen"
   releases for television/VHS/DVD which avoid the need for either "
   letterboxing" or the severe loss of information caused by conventional
   " pan-and-scan" cropping.

Sound

Data

Television add-ons

   Today there are many television add-ons including Video Game Consoles,
   VCRs, Set-top boxes for Cable, Satellite and DVB-T compliant Digital
   Television reception, DVD players, or Digital Video Recorders
   (including personal video recorders, PVRs). The add-on market continues
   to grow as new technologies are developed.

New developments

     * Ambilight™
     * Blu ray
     * Broadcast flag
     * CableCARD™
     * Digital Light Processing (DLP)
     * Digital Rights Management (DRM)
     * Digital television (DTV)
     * Digital Video Recorders (DVR)
     * Direct Broadcast Satellite TV (DBS)
     * DVD
     * Flicker-free (100 Hz or 120 Hz, depending on country)
     * HD DVD
     * High Definition TV (HDTV)
     * High-Definition Multimedia Interface (HDMI)
     * IPTV
     * Internet television
     * LCD and plasma display flat screen TV
     * SED display technology
     * OLED display technology
     * P2PTV
     * Pay-per-view
     * Personal video recorders (PVR)
     * Picture-in-picture (PiP)
     * Pixelplus
     * Placeshifting
     * Remote controls
     * The Slingbox
     * Timeshifting
     * Video on-demand (VOD)
     * Ultra High Definition Video (UHDV)
     * Web TV

Exterior designs

   In the early days of television, the cabinet was made of wood grain,
   however, the wood grain was disappearing in the 1980s. However, there
   has been a modern comeback of the woodgrain .

Geographical usage

     * Timeline of the introduction of television in countries

Content

Advertising

   Since their inception in the USA in 1940, TV commercials have become
   one of the most effective, most pervasive, and most popular methods of
   selling products of many sorts, especially consumer goods. U.S.
   advertising rates are determined primarily by Nielsen Ratings.

Programming

   Getting TV programming shown to the public can happen in many different
   ways. After production the next step is to market and deliver the
   product to whatever markets are open to using it. This typically
   happens on two levels:
    1. Original Run or First Run - a producer creates a program of one or
       multiple episodes and shows it on a station or network which has
       either paid for the production itself or to which a license has
       been granted by the producers to do the same.
    2. Syndication - this is the terminology rather broadly used to
       describe secondary programming usages (beyond original run). It
       includes secondary runs in the country of first issue, but also
       international usage which may or may not be managed by the
       originating producer. In many cases other companies, TV stations or
       individuals are engaged to do the syndication work, in other words
       to sell the product into the markets they are allowed to sell into
       by contract from the copyright holders, in most cases the
       producers.

   In most countries, the first wave occurs primarily on free-to-air (FTA)
   television, while the second wave happens on subscription TV and in
   other countries. In the U.S., however, the first wave occurs on the FTA
   networks and subscription services, and the second wave travels via all
   means of distribution.

   First run programming is increasing on subscription services outside
   the U.S., but few domestically produced programs are syndicated on
   domestic FTA elsewhere. This practice is increasing however, generally
   on digital-only FTA channels, or with subscriber-only first run
   material appearing on FTA.

   Unlike the U.S., repeat FTA screenings of a FTA network program almost
   only occur on that network. Also, Affiliates rarely buy or produce
   non-network programming that isn't centred around local events.

Social aspects

Alleged dangers

   Paralleling television's growing primacy in family life and society, an
   increasingly vocal chorus of legislators, scientists and parents are
   raising objections to the uncritical acceptance of the medium. For
   example, the Swedish government imposed a total ban on advertising to
   children under twelve in 1991 (see advertising). Fifty years of
   research on the impact of television on children's emotional and social
   development (Norma Pecora, John P. Murray, & Ellen A. Wartella,
   Children and Television: 50 Years of Research, published by Erlbaum
   Press, June, 2006) demonstrate that there are clear and lasting effects
   of viewing violence. In a recent study (February, 2006) published in
   the journal Media Psychology, volume 8, number 1, pages 25-37, the
   research team demonstrated that the brain activation patterns of
   children viewing violence show that children are aroused by the
   violence (increased heart rates), demonstrate fear (activation of the
   amygdala-the fight or flight sensor in the brain) in response to the
   video violence, and store the observed violence in an area of the brain
   (the posterior cingulate) that is reserved for long-term memory of
   traumatic events.

   A 23 February 2002 article in Scientific American suggested that
   compulsive television watching, television addiction, was no different
   from any other addiction, a finding backed up by reports of withdrawal
   symptoms among families forced by circumstance to cease watching.

   A longitudinal study in New Zealand involving 1000 people (from
   childhood to 26 years of age) demonstrated that "television viewing in
   childhood and adolescence is associated with poor educational
   achievement by 26 years of age". In other words, the more the child
   watched television, the less likely he or she was to finish school and
   enroll in a university.

   In Iceland, television broadcasting hours were restricted until 1984,
   with no television programs being broadcast on Thursday, or during the
   whole of July.

   Despite this research, many media scholars today dismiss such studies
   as flawed. For one example of this school of thought, see David
   Gauntlett's article " Ten Things Wrong With the Media 'Effects' Model."

Technology trends

   In its infancy, television was an ephemeral medium. Fans of regular
   shows planned their schedules so that they could be available to watch
   their shows at their time of broadcast. The term appointment television
   was coined by marketers to describe this kind of attachment.

   The viewership's dependence on schedule lessened with the invention of
   programmable video recorders, such as the Videocassette recorder and
   the Digital video recorder. Consumers could watch programs on their own
   schedule once they were broadcast and recorded. Television service
   providers also offer video on demand, a set of programs which could be
   watched at any time.

   Both mobile phone networks and the Internet are capable of carrying
   video streams. There is already a fair amount of Internet TV available,
   either live or as downloadable programs.

Suitability for audience

   Almost since the medium's inception there have been charges that some
   programming is, in one way or another, inappropriate, offensive or
   indecent. Critics such as Jean Kilborne have claimed that television,
   as well as other mass media images, harm the self image of young girls.
   Other commentators such as Sut Jhally, make the case that television
   advertising in the U.S. has been so effective that happiness has
   increasingly come to be equated with the purchasing of products. George
   Gerbner has presented evidence that the frequent portrayals of crime,
   especially minority crime, has led to the Mean World Syndrome, the view
   among frequent viewers of television that crime rates are much higher
   than the actual data would indicate. In addition, a lot of television
   has been charged with presenting propaganda, political or otherwise,
   and being pitched at a low intellectual level.

   Retrieved from " http://en.wikipedia.org/wiki/Television"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
