The
scanning technique of a television is a process similar to the reading of
written information on a page; starting at the top left, and progressing line
by line downwards to the end at the bottom right. The picture is not
instantaneously read off; it takes a finite though small scanning time. The
brightness information at the picture elements in the picture is converted into
electrical signals at a photosensitive surface exposed to the optical image of
the picture on one side and scanned by an electron beam on the other side.
scanning technique of a television is a process similar to the reading of
written information on a page; starting at the top left, and progressing line
by line downwards to the end at the bottom right. The picture is not
instantaneously read off; it takes a finite though small scanning time. The
brightness information at the picture elements in the picture is converted into
electrical signals at a photosensitive surface exposed to the optical image of
the picture on one side and scanned by an electron beam on the other side.
The
scanning is done line by line, horizontally from left to right at a fast rate,
and vertically from the bottom at a slower rate as illustrated in figure 1
below.
scanning is done line by line, horizontally from left to right at a fast rate,
and vertically from the bottom at a slower rate as illustrated in figure 1
below.
The
retrace of the beam is very fast compared to the forward scan, and scanning
during retrace or flyback is blanked by cutting off the beam during the
horizontal and vertical flyback intervals. The picture is thus scanned for its
brightness information over a finite number of lines in it. The larger the numbers
of lines, the greater are the details of the picture scanned.
retrace of the beam is very fast compared to the forward scan, and scanning
during retrace or flyback is blanked by cutting off the beam during the
horizontal and vertical flyback intervals. The picture is thus scanned for its
brightness information over a finite number of lines in it. The larger the numbers
of lines, the greater are the details of the picture scanned.
During
reproduction, an exactly similar scanning process is used synchronously with
that at the sending end. The scanning electron beam in the picture tube
‘paints’ the television picture on the viewing screen by producing proportional
glow at the corresponding points. The scanning rate is fast enough to create an
illusion of continuity because of the persistence of vision of the human eye.
reproduction, an exactly similar scanning process is used synchronously with
that at the sending end. The scanning electron beam in the picture tube
‘paints’ the television picture on the viewing screen by producing proportional
glow at the corresponding points. The scanning rate is fast enough to create an
illusion of continuity because of the persistence of vision of the human eye.
