cameras not only use a special tube for each chrominance channel, but have
special color-correction filters and electronic circuits as well.
(2) Resolution. The camera pickup tube is the principal element in
the camera that determines the crispness of the picture.
Other elements
that influence the resolution of the picture are the lens, the quality of
the internal optical system, and, of course, the TV set on which you see the
picture reproduced. The power of resolution in a pickup tube is very much
like printing.
(a) For instance, take a magnifying glass and look at a photo that
is reproduced in a newspaper. Then look at one in a slick magazine. You
will notice that the newspaper picture consists of rather coarse dots,
whereas the individual dots are barely discernible in the magazine picture.
The newspaper picture has a lower resolution than the magazine picture.
(b) As pointed out earlier, manufacturers are trying to make a
small camera pickup tube that produces a high-resolution image.
For the
present, however, the large-format tubes still have a better resolution than
the 1/2-inch and 2/3-inch tubes and are, therefore, preferred for the high-
quality studio cameras.
(c) So far, the CCDs have a considerably lower resolution than the
quality camera pickup tubes.
The lower the resolution of the camera, the
less fine picture detail it can show.
(d) Special electronic devices, called image enhancers, are
generally used to sharpen the picture detail as delivered by the camera,
However, although this device can enhance the image as delivered by the
camera, it cannot invent detail the camera did not see in the first place.
(e) You should be conscious of the limited resolution of the TV
picture, especially when dealing with television graphics and similar areas
of production where fine picture detail predominates.
(3) Operating light level.
Because it is the job of the camera
pickup tube to convert light into electricity, the camera needs some light
to produce a video signal and requires a specific amount of light to produce
an optimal image. Most color cameras need an operating light level from 100
to 250 foot candles of illumination.
(a) You will hear and read that certain cameras can produce
pictures with "full video," meaning that the video signal has a certain
prescribed intensity, with as little as 3 foot candles of illumination.
There are certain electronic devices that compensate for the lack of
illumination, such as the gain control, which boosts the brightness of the
picture, and the bias light, a small light that illuminates evenly the front
surface of the camera pickup tube, providing a weak video signal even if no
light comes through the lens.
(b) Neither of these devices can entirely prevent the various
negative effects of minimal levels of illumination, such as video noise,
lag, and color distortion.
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