Чтение общенаучной литературы. Кытманова О.А. - 26 стр.

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27
and a third a filter passing only blue light Mirrors allow the image of the studio
scene to fall on each tube. The tubes work exactly as described for black-and-white
television and each tube produces a video signal and a stream of pulses. The signal
from the red-filtered camera represents red parts of the scene and the signals from
the other two represent the green and blue parts. Modern cameras, especially
cheaper ones, use fewer tubes. The light-sensitive coating, similar to that found in
black-and-white cameras, is covered by a colored filter mosaic to produce separate
color signals. If the three sets of camera signals were amplified and fed to three
cathode ray tubes, one with a red-glowing phosphor, one with a green, and one
with a blue, and the resultant pictures were combined by mirrors, the screen would
be in full color - not merely reds, greens and blues but all the colors of the original
scene. This is how television projectors work.
The band of frequencies taken up by the transmission of three separate video
color signals IP about three times that taken up by a black-and-white station, which
is uneconomical The problem is solved by transmitting a high-definition black-
and-white picture and filling it in with color, with very much less detail. This is
perfectly acceptable to the human eye The color information is contained in a
subcarrier wave which is added to the "black-and-white" signal so as to take up no
extra band-width, and is hardly noticeable on Color television depends upon the
fact that nearly alt colors can be produced by combining three primary colors of
light in the correct proportions. The diagram shows what happens when three
beams of light, red, green, and blue, are projected on to a white screen to overlap
.This form of color combination, called "additive mixing", works only with light,
and not with pigments such as paints or inks, so the diagram can only give a rough
idea of the effect Additive mixing of red, green, and blue light gives the following
colors. red plus green forms yellow, red plus blue forms magenta, green plus blue
forms cyan; red plus green plus blue forms white a black-and-white receiver, so
that the system is compatible. In this way, all the three-color information is
squeezed into a frequency band no wider than that occupied by a black-and-white
station. At the receiver the three separate cathode ray tubes described for the
simple system are combined in one tube. The viewing end is a screen carrying
about 1.7 million phosphor dots arranged in tiny triangles. When hit by an electron
beam one dot in the triangle glows red, another green, and the third blue. Three
electron guns are mounted at the other end. A shadow mask, consisting of a metal
plate pierced with tiny round holes, prevents a beam from hitting phosphor dots of
another color; that is, the beam from the green gun can hit only the green-glowing
dot in each triangle When each dot in a triangle is hit at In the shadow mask tube
many electrons are blocked by the mask But in the Trinitron tube the metal grille
allows more electrons through to the phosphors and so produces a brighter
television picture the same time by its individual beam all three glow but as they
are so close together the eye sees them as a dot of white light The Trinitron tube
developed in Japan uses a single electron gun to produce three in line beams .The
mask is slotted and the three color phosphors instead of being in the form of dots
consist of large numbers of very narrow strips repeated across the face of the tube.
This gives exceptionally sharp pictures Other types of in-line" tubes using slots and

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