What is the difference between analog and digital television?
Analog television service is the traditional
method of transmitting television signals. Analog transmission has been the standard
broadcast technology since the inception of television. As a technology, analog
is the process of taking an audio or video signal and translating it into electronic
pulses or radio frequency (RF) waves. Understandably, the electronic pulses are
subject to interference, which is what can give a "snow" effect.
Digital, on the other hand, breaks the signal into a binary format where the audio or video data is represented by a series of "1"s and "0"s. This signal is less susceptible to interference and allows far more data to be transmitted in a compact way.
Televisions generate their pictures by
rapidly drawing a succession of horizontal lines across the screen with an electron
beam, exciting the phosphorescent screen coating to create patterns of light on
the surface. This is called scanning, and each of the lines drawn by the electron
beam is known as a scan line. On a traditional analog TV, there
are 525 scan lines that comprise the image, 480 of which are actually visible
onscreen.
Analog TV fills the screen by executing two alternating
passes of the electron beam: The first pass hits the odd lines in the sequence
(1-479) and the second fills in the even lines (2-480). Each of these two groups
of lines is known as a field, and the combination of two fields
(encompassing all visible scan lines) is known as a frame. An
analog TV draws one field every 1/60th of a second, completing a full frame 30
times per second. Because the two fields are interlaced to form a frame, this
is called an interlaced scan.
Digital TV's advantage lies in the speed at which
it is capable of drawing these scan lines. Rather than building a frame from two
interlaced fields, a digital display can complete a progressive scan
of all 480 lines (in sequence from 1-480) every 1/60th of a second — the
same amount of time an interlaced display takes to fill just half the screen.
The result is a visibly fuller, sharper picture, with virtually none of the striping
visible on a conventional TV. The picture is also noticeably brighter, since twice
as much screen area is illuminated by the electron beam in the same period of
time. These characteristics are particularly important as the size of the display
increases — a progressive-scan picture looks much more solid and real when
blown up to super size on today's mega projection screens.
Furthermore,
the characteristic "flicker" associated with interlaced scanning (particularly
problematic when the image contains fine horizontal details that are present in
only one of the two interlaced fields) is noticeably reduced with progressive
scanning, making it easier on your eyes. Less eye fatigue means more distraction-free
enjoyment.
Be moved without losing your edge
With moving images, the advantages of progressive scan are even more pronounced.
When tracking fast-moving images across the screen, interlaced displays are plagued
by significant distortions known as motion artifacts. This is
because most true video sources actually generate 60, not 30, unique images per
second. Interlaced displays represent each of these 60 unique stills, but each
uses only half of the screen's available scan lines. When an image moves quickly
across the screen, the difference in its position from one field to the next becomes
apparent, and the interlacing visually combines disparate fields, creating an
effect known as "feathering" or "combing." Image definition
becomes blurry and indistinct when movement occurs, but clarity is restored once
the image becomes stationary again.
By contrast, since a progressive-scan
display is capable of reproducing an entire frame for each unique still in the
video stream, it can render moving objects with much greater clarity. Each frame
appears cohesive, with no trace of the artifacts that make the interlaced display
appear to lose focus when objects move.
Additional
Sources:
http://www.pmcusa.com