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Thread: DMC

  1. #1
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    DMC

    Hello,

    I am trying to understand the DMC algorithm(s) and some of its improvements. By doing so, several questions occurred.

    First, in the generalized setting over arbitrary alphabets: Does one
    need to encode the escape symbol (as in PPM) or is it just used to follow
    some path in the automaton (until one can estimate the probability
    of the current symbol).

    Second, Nania Francesco Antonios hook compresser seems to be the
    DMC implementation with best compression ratio (LTCB). He describes
    an improvement of the original algorithm which he calls ADMC (Advanced DMC). I have to admit that I could not follow those explanations.
    Maybe someone (Nania?) could explain it again.

    Third, are there any further (public) improvements to the original algorithms (despite combination with PPM or other compression algorithms)?

    Thank you,
    Alibert


    P.S. Apologies for bothering you with these questions - I am rather new to this field of data compression, so please be patient...

    Great forum!

  2. #2
    Programmer osmanturan's Avatar
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    Quote Originally Posted by Alibert View Post
    ...Third, are there any further (public) improvements to the original algorithms (despite combination with PPM or other compression algorithms)?
    First of all, willkommen

    DMC algorithm is interesting for me too. You can find a compact design in PAQ8 series compressor. In PAQ8 series, DMC produces prediction as a submodel. So, actually it's different from hook implementation. But, I think, you will find it useful to understand for what's going on.

    If you are curious about DMC performance, you can also check mcomp from WinRK's site. There is a bit different implementation in mcomp. You can read small details about it from the blog.

    Osman

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    Thank you for the links, osman.

    Do you know any approaches for "size restriction" of the automaton other than deleting the complete automaton (and partly rebuilding it from the last fragment of the input)? I was wondering whether other techniques such as minimization of finite state machines can be adapted.

    Cheers,
    Alibert
    Last edited by Alibert; 4th November 2008 at 09:43. Reason: Typo

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    Freehook

    Does anybody of you know where to find freehook 0.3 sources?

    Is there any newer version out there?

    Thanks in advance,
    Alibert

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    Administrator Shelwien's Avatar
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    Quote Originally Posted by Alibert View Post
    Does anybody of you know where to find freehook 0.3 sources?
    http://www.geocities.com/lovepimple_mail/

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    @LovePimple: Thank you for the link. My original starting point
    has been LTCB, but there the link is obsolete. Maybe Matt
    would like to use your's.

    @Shelwien: I do not like the presentation of DMC in wikipedia.
    In particular, I think using a "table" for the description of
    the algorithm is inappropriate. DMC is based on an edge-weighted
    directed graph (which of course can be implemented as a table).
    Nevertheless, thank you for the link.

    Cheers,
    Alibert
    Last edited by Alibert; 7th February 2009 at 10:31. Reason: Typo

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