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The
TV Camera > How TV Works > Rows
of Dots
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Sorry it's a bit squashed, but this
cool clip makes it very easy to understand
how a TV picture can be made up of
tiny dots.
(No Sound)
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Before
we actually get to the television camera, let's start
with a basic lesson in how television actually works.
ROWS
OF DOTS:
If you put a magnifying glass up to your TV, you'd see
a bunch of dots. Lots and lots of dots—arranged
in neat little rows. How many rows? 525 to be exact,
but we'll come back to that.
These
dots are actually bits of phosphor on the inside surface
of your TV screen. The neat thing about phosphor is
that when an electron beam hits it, phosphor glows for
a moment—it gives off light.
The
illustration at the right zooms in on the picture of
Einstein to reveal how an image can be built from lots
of individual dots. (After you play the clip, try moving
through it with the slider.)
So,
inside your TV, an electron beam hits the phosphor dots
and they glow. What is amazing is that only ONE dot
is lit up at any given instant. It's just one dot at
a time.
Yet
it seems like your whole TV screen is always on. So
how can it be just one dot at a time? Two reasons, really:
1) The dots light up in very rapid succession.
Fast. Really fast.
2) After a dot lights up, it glows for a brief
moment. That glow continues for a split second even
after the electron beam has moved on to the next dot.
SCANNING:
All this dot-glowing is done in a very orderly fashion
called "scanning." To understand scanning,
think of typing words on a page. You only type one letter
at a time (just like scanning lights up one dot at a
time). When you finish typing a line, you move on to
line number 2,3,4 etc. (again, scanning does the same
thing).
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