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Re: Digi Beta versus D1

Michel Lapointe writes:

<< My question to everybody: Is there a way of knowing , by examining the
final  D1 tape, that digi Beta was used in the process, for maybe 2-3
generations. The answers I got so far are inconclusive. I am being told about
possible picture content induced artifacts but without [ ... ] >>

There are two flavors of video compression: lossy and lossless.  Lossy
compression is what happens in MPEG and JPEG; it means that something is taken
out of the video.  On playback, it may look close enough to the original video
for TV, but it will not be identical to the original material, generally
speaking.  Subtle or not, artifacts are thereby introduced.  The exact form
they take is hard to predict, as that depends on the nature of motion and
detail in the image, as well as the  compression system.  Since the process
cannot be reversed this type of compression is only used sparingly in post

Lossless video compression schemes are somewhat similar to computer file
compression utilities like PK-Zip, which are capable of restoring compressed
data files back to their exact, original state.  In video, DCT and Digital
Betacam fall into this category, but with one important difference: due to
time limitations, the process can't always be perfect.  It usually makes
little difference to a computer if one file takes slightly longer to compress
than another.  In video, however, the next frame is due in 1/25 or 1/30 of a
second, and can't be put on hold.  So video compression algorithms are allowed
to "break" should there be too much going on in a frame to cope with.  Again,
exactly what makes this happen, and what it will look like are highly
dependent on the nature of the image, and the particular compression scheme.
Excessive randomness and diagonal motion are two things that have been known
to cause so-called lossless schemes to introduce blockiness in images.
Anecdotal evidence is that after several generations,
compression/decompression errors also have a way of piling up.  

Practically speaking, however, the fact that Digital Betacam is a popular and
widely used format indicates that whatever artifacts it has, they are
inconsequential for the vast majority of situations.  

If mastering to D-1 is problematic, but an uncompressed digital videotape
format is called for, you might want to suggest D-5 next time.  While the
format uses mild audio compression, standard 601 digital video goes through
untouched by it.

Best regards,
Christopher Bacon

(Not affiliated with any video equipment manufacturers.)

Thanks to Tom McMahon and Microsoft for support in 1998.
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