ADS Technologies USBAV-708 INSTANT VIDEOMPX, User Manual

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The
Guide
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Int
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Wh
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Interlacing is a method adopted from the old days of analogue television that
allowed the frame rate of a video to be doubled by broadcasting only half a frame
at a time. This was achieved by dividing each frame into two fields, each
occupying alternating horizontal lines. We call these the top and bottom fields.
Here you see two fields composing one
frame of video. First the top field is
broadcast and scanned out on odd lines
by the television, then the bottom field is
broadcast and scanned out on the even
lines. In this way a complete picture is
recreated.
An interlaced camera may capture all
the even lines in the picture first and
then the odd lines a fraction of a second later, leading to jagged edges that
appear where there is motion in the reconstructed frame.
Consideration of interlacing is important to DivX encoding because some sources
(notably DV video and some DVDs) are interlaced and will suffer severe quality
degradation and artifacting if encoded without respect to interlacing.
What is interlacing?
Interlacing
The complete frame
Bottom field Top field