Image Processing Reference
In-Depth Information
observe some digital compression artifacts in the analog service but it will be too late to
remedy them by then.
17.4
Professional Recording Formats
Many different professional formats have evolved over the years. The current preferred for-
mat for high-quality work is Betacam, but even within that format there many varieties. The
latest one is called IMX. This is an improvement over Digital Betacam but uses similar car-
tridges. Here is a list of common professional recording formats you might encounter:
Betacam
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Digital Betacam (Digi-Beta)
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Betacam SP
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Betacam SX
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Betacam IMX
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DVC Pro
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DVCAM
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HDCAM
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XDCAM
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17.5
Recording Off the Air
Analog broadcast quality varies considerably according to the atmospheric conditions,
and periods of high pressure or very hot, dry days affect the signal propagation, which
leads to more noise in the picture. Summertime weather conditions change the propaga-
tion such that reception of signals from transmitters that are very far away might cause co-
channel or superimposed-vision artifacts. An aerial antenna that is surrounded with trees
saturated by rain will cause ghosting of the image or echoes.
Once these artifacts are in the recorded material they are very hard to remove. Some
of them (ghosting and co-channel artifacts, for example) will play havoc with your com-
pression ratio.
17.5.1
NTSC Off Air
In the United States, outside of a studio environment, digitizing and encoding video that
was taken off air from an NTSC broadcast results in a 525-line picture running at 29.97 fps.
If we care enough to keep them rather than buy new DVD copies, any movies must have
the pulldown frames removed. This content is also interlaced. If the original progressively
scanned source material were available, encoding from that would be better than trying to
recover the progressively scanned version from the interlaced broadcast. De-interlacing
that movie footage by removing the pulldown is a vital first step. That may not be easy if
the footage has been processed with edits and overlays being added after conversion to
the interlaced format.
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