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Re: Information, Compression, and storage.




---------------Original Message---------------
At 08:01 PM 7/6/99 -0400, Christopher Bacon wrote:
>There are a few types of video compression that are theoretically lossless
>(meaning that they can be completely reversed).  These include DCT, wavelet,
>and fractal.  ...

Maybe it would help to clarify that DCT is a TRANSFORM, ie, another way of
representing the signal.  The mathematics of the transform are such that the
process is reversible without loss.  However, the whole purpose of applying
the DCT (discrete cosine transform) to the signal is to allow us to also
apply algorithms to reduce bit-rate (compression) by making intelligent
choices as to which information can be removed*.  JPEG and MPEG are also
based on the DCT.  Not to be confused with the DCT product line from Ampex,
which happened to use discrete cosine transofrms in its compression scheme.

* How much and when and where to remove information are based on design
parameters such as available bandwidth, bitrate and desired picture quality.
The choice and implementation of the bitrate reduction algorithms are what
define the overall quality charactersistics of a particular format or 
compression scheme.

Those interested in a more formal look at this should hit the Tektronix
info on picture quality analysis (PQA).



----------End of Original Message----------

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"Trust the computer industry to shorten "Year 2000" to Y2K. It was
this kind of thinking that caused the problem in the first place."
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Bill Topazio, VP/Engineering     bt at mte.com     v:212-907-1225
Manhattan Transfer               New York, NY   f:212-687-2719
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