| Television is a communication system for the broadcasting and reception of
moving pictures and sound from a distance. Television is based on the
principle of the sequential broadcasting of picture elements with the help
of scanning. The frequency of a picture change is selected, mainly, by
the criterion of the smooth broadcasting of motion. Interlace scanning is used
to reduce the transmission frequency bandwidth. It allows in
increasing the picture frequency by two times (that means, to reduce the
flickering of the screen) without changing the resolution of the frame.
In a general view, a television channel includes the following devices:
1. Video camera: The lens projects the image on a photosensitive
surface. Along the lines, the scanning circuit senses the
brightness of the elements of the image. First, odd lines (field
1) are transmitted and then the even (field 2) are
transmitted. Information about the color is transmitted on a sub
carrier frequency. Thus, the picture of a full color television
signal is formed. Specialized document-cameras are
used to shoot and transfer documents.
2. Video recorder (not compulsory): Records and reproduces
the alternation of lines and fields at a required moment.
3. Transmitter: The radio frequency signal is modulated by the television
signal and broadcasted (the translation along the cable is
possible). Sound is transmitted on a separate frequency usually
by means of frequency modulation.
4. Receiver: Television. With the help of sync pulses, the television
picture is developed on the screen (CRT, LC panel, plasma
panel) in the exact order of succession of the image lines.
Distribution of video programs on cassettes and compact discs (even
though it is not considered as telecasting) is widely used.
It is accepted to name the set of picture details, pictures or field change
frequency and occurrence of interlacing as a television broadcasting
standard. Three standards with interlace scanning (interlacing) have existed
in the world for several decades:
* 625 lines, 50 fields per second in Europe and Australia (PAL)
* 525 lines, 59.94 fields per second in America and Japan (NTSC)
* 625 lines, 50 fields per second in France, Russia, China and several
countries of Near East (SECAM)
Now, high definition TV is about to replace the existing standards.
History:
TV technologies have not been invented by a single person and in a
single shot. Television is based on the invention of
the photo-conductivity of selenium, made by Willoughby Smith in 1873.
The invention of the scanning disk by Paul Nipkow in 1884 served as the impetus in
the development of a mechanical TV, which was popularly used right up to
1930.
To date, the place of the invention of the electronic television system is
disputed. Different versions talk about Germany and also about
Great Britain, and boldly, even Hungary and Uzbekistan claims
to be the inventors. Russian historians claim that the TV was invented in
Russia, in St. Petersburg by professor B. L. Rozing, who in 1907,
presented the first trial electronic system of the TV. However, subsequent
development and commercial introduction was done in the USA thanks to
V. K. Zvorykin, a student of B. L. Rozing.
Color TV was invented by O. A. Adamyan
In the second half of the 20th century, TV became widely popular. Its role in the
world was emphasized by the UNO by declaring a commemorative day - World TV
Day.
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Sony became the latest major electronics manufacturer to drop its production of rear-projection TVs, and focus on liquid crystal display (LCD) TVs and organic light-emitting diode (OLED) TVs. The sales or rear-projection TVs are dropping so fast that it became a losing business unit for Sony and some other TV manufacturers. The sales of classic CRT (cathode-ray tube) TVs are also dropping fast in favor of LCD and plasma TVs, and analysts predict that CRT TVs may completely disappear from US and American shop shelves in the next 24 months. The same thing happened with VCRs when DVD players took over years ago.
