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This is my yr 10 Media Assignment I am doing it on television.Advances in
Technology
The Colour television
Color television employs the
basic principles of
black-and-white television. The
essential difference is that a
color broadcast is in reality
three telecasts in one. The
screen of a color receiver
actually displays three images
superimposed on each other;
these images present,
respectively, the red, green,
and blue components of the
colors in the scene. This use of
three primary colors in the
television follows the method
used in color photography and
color printing, in which three
layers of colored dyes (in
photography) or three
interspersed sets of fine
colored dots (in printing) give to
the eye the impression of all
the natural colors.
The Black White Television
The principal elements of a
typical black-and-white
television camera are the lens,
the camera tube, and the
scanning and focusing coils.
The lens (which is often of the
zoom type, particularly in
sports telecasting) focuses the
scene on the front end of the
camera tube.The tube that was
most widely used in the late
1970s was the vidicon,
which is an evacuated glass
cylinder. At the front end of the
tube is a flat glass plate, the
inside of which iscoated with a
photosensitive material, a
sulfur compound of
antimony.(Another widely used
tube, the plumbicon, is similar
to the vidicon in operation but
uses a compound of lead.)
Underneath the antimony
coating is a thin, transparent
coating of metal.The electrical
resistance ofthe antimony
compound is lowered when light
falls on it. The optical image
from the lens falling on the
antimony coating causes its
resistance to change in
proportion to the amount of
light reaching it at each point
on its surface; that is, a pattern
of electrical resistance is
formed that matches the
pattern of light in the
image.The metallic coating
beneath the antimony coating is
maintained at a positive
voltage, causing each point on
the antimony coating to assume
a positive charge, with the
amount of charge depending on
the amount of light falling on
that point. Thus a pattern of
positive electric charge is built
up, and the charge elements
corresponding to the picture
elements pass through the
antimony to its rear surface,
where
they are stored.At the opposite
end of the camera tube is a
structure known as an electron
gun. This forms a narrow
ELECTRON BEAM that
travels down the tube and
encounters the charge pattern
on the rear of the antimony
coating.The focusing coils are
arranged to keep the electron
beam
narrow (that is, sharply
focused) so that the beam that
strikes the coating has the size
and shape of the picture
element.The scanning coils are
arranged to move the electron
beam over the stored charge
image in the interlaced
scanning pattern previously
described. In this manner, the
electron beam reads the stored
charge image, line by line. By
the time the scanning of the
image is completed, the charge
The electrons have negative
electrical charge.When they hit
a point on the antimony coating,
they neutralize the positive
charge stored at that point.
This sudden change in charge is
registered as a change in
voltage on the metallic coating,
which is connected to the
camera terminal. As the
electron beam scans the charge
image, it thus produces a
succession of voltage changes
at this terminal, which
constitute the video signal. The
video signal at the camera
terminal is weak, so it is
amplified at once within the
camera housing. After further
processing, the amplified video
signal is transmitted to the
receiver, where it reaches the
picture tube and re-creates the
image.
History of The Television
The first proposals for
television were made long
before the electronic
techniques of the present day
were developed. In the 1880s
the first proposal to transmit
images by scanning was made
by W. E. Sawyer, an American,
and by Maurice LeBlanc of
France.Black-and-White
Television A few years earlier,
in 1873, the fact that the
electrical resistance of
selenium (later used in early
versions of the vidicon camera
tube) was lowered when the
material was illuminated was
discovered by Louis May, an
English telegrapher. In 1884
the German Paul Nipkow
invented a mechanical system
of scanning an image through
holes in a rotating disk, but not
until 1926 did the Englishman
John Logie Baird and the
American Charles F. JENKINS
actually demonstrate the
transmission of images in
halftone using the Nipkow
disk.The development of
electronic methods began in
1897 when the German
Ferdinand BRAUN produced
the first CATHODE-RAY
TUBE, the ancestor of the
picture tube. In 1907 the
Russian Boris Rosing
suggested the use of Braun's
tube to reproduce television
images. Using a rotating mirror
drum for scanning, Rosing
actually transmitted crude
geometrical shapes but was
unable to reproduce halftone
images.In 1908 the Scotsman
A. A. Campbell-Swinton
proposed that the image be
stored in the form of electric
charge in a camera tube and
reproduced on a picture
tube--the essential features of
today's system. The crude
techniques of that day did not
permit the system to be
realized in practice, and not
until 1923 did the American
Vladimir R. ZWORYKIN, who
had studied in Russia under
Boris Rosing, apply for a
patent for a camera tube
(iconoscope) that used a
stored-charge
image.Meanwhile, the
techniques of signal
amplification using vacuum
tubes had advanced to the point
that, wholly by electronic
methods, signals from
Zworykin's iconoscope could be
transmitted by wire to a picture
tube. The transistor, invented
in 1948, later replaced the
vacuum tube and in turn led to
integrated circuits.By the early
1930s experimental broadcasts
of black-and-white halftone
images, composed of 343
scanning lines, were conducted
by engineers of the Radio
Corporation of America (now
RCA). By 1935, English
engineers had developed a
broadcast system using 405
scanning lines. The first
telecasts regularly scheduled
for the public began in London
in 1936 using this system. (A
mechanical system using 240
lines was also broadcast but
soon abandoned because the
electronic system was clearly
superior.) Experimental
broadcasts using 441-line
images began in New York that
same year, but not until 1941
did the Federal
Communications Commission
authorize public broadcasting in
the United States using 525-line
images. This effort was held in
abeyance during World War II.
After the war black-and-white
broadcasting developed rapidly
in the United States, England,
France, and Germany. One
million receivers were in use in
America by 1949, 10,000,000
by 1951, and more than
100,000,000 by 1975.
One of the show's sponsors, Wonder Bread, put paper
ballots in its loaves as a sales gimmick, and thousands
of children mailed in their votes for Howdy. Rumors
spread after Election Day that Howdy Doody had
received thousands of actual write-in votes. If true, it's unlikely that Howdy's votes affected the
outcome of the election. "Puppet Playhouse" was televised only on the East Coast, which Dewey
carried anyhow. Truman won the election in the Midwest and West, which had few TV stations and
no "Howdy Doody." www.fortunecity.com
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Jennifer Anniston
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