Image Processing Reference
In-Depth Information
PAL Off Air
In the United Kingdom and Europe, off-air content will be from a PAL broadcast. The pic-
ture resolution is a little higher at 625 lines but the frame rate is lower at 25 fps. It will also
be interlaced and will not have the pulldown since 25 fps is close enough to just run the
24-fps movie a little bit more quickly.
Generational Loss
Every time you re-record the video from one tape to another, there will be some degrada-
tion in quality. When you use analog video, the degradation is quite noticeable each time
you dub the video. The generational loss is supposed to be eliminated when you record
the video digitally. But this is only the case if no format conversion takes place during the
digital transfer. Changing the encoding from one type to another results in generational
losses even in the digital domain.
You should always work at the highest quality possible. Ideally your source will be
uncompressed material. Apply the final compression down to the desired format in one
step. Keeping the number of intermediate stages to a minimum helps improve the quality
of the finished product.
Being aware of the compression process helps you make informed choices about what
format conversions you are going to allow during the workflow.
Tape Formats and Recording Modes
Note that on your domestic players, the short-play and long-play modes may be called SP
and LP, respectively. Always avoid LP when possible. SP will yield the best quality available.
You might argue that the Betamax format is actually better than the S-VHS short-
play format but this might depend on the grade of the tape, how old the recording is, and
all sorts of factors including the source of the tape recording.
Other important considerations are tape tension and head wear. The playback/record
head in the VCR might be worn by overuse. The age of the tape heads and the tape ten-
sioning will materially affect the quality of analog playback. Tape tension will affect the
synchronization and time-base correction may need to be applied in order to get a reliable
signal. You may also get those horrible little tearing patterns in the bottom few lines of the
Quality Issues With Different Source Formats
There are many different formats from which you might source your original material.
Some will present you with no problems since they are high quality. Where you will expe-
rience some difficulty is in trying to get the best out of the lower-quality consumer formats
that you might be sourcing your content from.
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