🚀 go-pugleaf

In article <...> madler@cco.caltech.edu (Mark Adler) writes:
> Actually, I have my own terms for those things that I would now like
> to propose for general adoption: I call coding of redundancy and
> entropy and any other sort of lossless compression "source-coding",
> since it depends on characteristics of the source.

> Selectively tossing out information for compression, for example
> visual or audio information not considered perceptible, I call
> "sink-coding", since it depends on characteristics of the
> eventual destination of the data, which can be called the sink.

    These  are  semantics  issues,  but  the  subtle  interpretations  of  the
    terminology are important.  Each term communicates different connotations.
    The problem with using "source" and "sink" is that they are used  in  many
    other  ways,  and can quickly confuse the issue.  Especially when speaking
    verbally, when "sink" and  "synch"  (as  in  synchronization)  can  become
    confused.   Remember,  that  if you are sending video information, part of
    the channel includes "synch" pulses.

    There is no set terminology.  However, some terms you  will  find  in  the
    literature which span the ideas you are talking about are:
    A.  LOSSLESS COMPRESSION
        This communicates that no  information  is  lost.   Categories  within
        lossless  compression  describe  the  methods used to achieve lossless
        compression.
    B.  LOSSY COMPRESSION.
        Of course, this communicates that the information content is reduced.

    Two other terms are used to describe the what Mark refers to  as  "source"
    and "sink" coding:
    i.  REDUNDANCY CODING
        This is implies entropy coding; some means of de-correlating the data.
    ii. RELEVANCY CODING
        This codes only the information which is relevant.  So, if  the  Human
        is the final destination, and the the information is below perceptible
        levels it is not relevant.  If you are transmitting radar data between
        FAA  flight  controllers,  the relevant information might be location,
        altitude, and velocity.

    For humans observers, the terms: "visually  lossless"  (images),  "audibly
    lossless"  (audio),  or  "perceptually lossless" (both or either), connote
    relevancy coding.

	- Thomas

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