The
scene or the picture to be televised is focused with the help of a lens system
onto a photosensitive target near the faceplate of the camera pick-up tube to
form an accurate, well-defined image in it. The surface of the target plate may
be regarded as a mosaic formed by a very large number of elementary areas. As
the surface is photosensitive, the electrical state of each minute area varies
in accordance with the intensity of light falling on it at a particular
instant. The minute photoelectrical elements on the surface of the target plate
produce an electrical pattern corresponding to the picture illumination.
scene or the picture to be televised is focused with the help of a lens system
onto a photosensitive target near the faceplate of the camera pick-up tube to
form an accurate, well-defined image in it. The surface of the target plate may
be regarded as a mosaic formed by a very large number of elementary areas. As
the surface is photosensitive, the electrical state of each minute area varies
in accordance with the intensity of light falling on it at a particular
instant. The minute photoelectrical elements on the surface of the target plate
produce an electrical pattern corresponding to the picture illumination.
The
electrical response of each minute element is read off with the help of an electron
beam circuit to produce electrical impulses. The elements are scanned in a
predetermined sequence and speed so that an electrical waveform with respect to
time is generated to represent the brightness information at various points in
the picture. The target plate is held at positive potential with respect to the
cathode of the pick-up tube and the actual beam current varies in accordance
with the electrical state of the picture element (pixel) being scanned at a
given instant, thus producing a varying voltage across a resistor through which
the beam current is made to pass.
electrical response of each minute element is read off with the help of an electron
beam circuit to produce electrical impulses. The elements are scanned in a
predetermined sequence and speed so that an electrical waveform with respect to
time is generated to represent the brightness information at various points in
the picture. The target plate is held at positive potential with respect to the
cathode of the pick-up tube and the actual beam current varies in accordance
with the electrical state of the picture element (pixel) being scanned at a
given instant, thus producing a varying voltage across a resistor through which
the beam current is made to pass.
The
beam scans the image horizontally by means of a magnetic field set up by the
horizontal deflection coils which are supplied with the required sawtooth
currents for linear deflection. Simultaneously, the beam proceeds vertically
downwards slowly by means of the magnetic field of vertical deflection coils
which are also supplied suitable sawtooth currents. The scanning must be done
at a fast speed over and over again so that the changing or moving pictures can
be considered as steady for the scanning period.
beam scans the image horizontally by means of a magnetic field set up by the
horizontal deflection coils which are supplied with the required sawtooth
currents for linear deflection. Simultaneously, the beam proceeds vertically
downwards slowly by means of the magnetic field of vertical deflection coils
which are also supplied suitable sawtooth currents. The scanning must be done
at a fast speed over and over again so that the changing or moving pictures can
be considered as steady for the scanning period.
