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Thread: LZWA vs. LZC

  1. #1
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    Here are some testing results of different LZW coders:
    Test file ENWIK8 (size 100,000,000 bytes)

    compress 4.3d (LZC with 16-bit dictionary):
    45,763,941 bytes

    LZWA16 (LZW+Flat arithmetic compression with 16-bit dictionary):
    44,150,300 bytes

    TC 4.3 (Enhanced LZC with 18-bit dictionary):
    41,812,930 bytes

    LZWA20 (LZW+Flat arithmetic compression with 20-bit dictionary):
    37,825,854 bytes

    For comparison:
    pkzip 2.0.4 (Deflate):
    36,934,712 bytes

    Conclusions:
    LZW+ARI compressors still lightning fast and needs no memory, plus have fastest decompression, but compression is really poor and I think no reason to release a new compressor based on LZW+ARI! What do you think?

  2. #2
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    In addition, you can read this paper about LZW:
    Improving LZW (23 KB)

  3. #3
    Guest
    Interesting, thanks!

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    I'll countinue experimenting with LZW+ARI. Here are some test results.
    LZW+ARI was tested with different dictionary sizes (9-16 bits):

    File 'pak0.pak' from Quake 2 game (as a mixed-data test-file), 183,997,730 bytes:

    LZWA with 10-bit dictionary: 121,409,481 bytes
    LZWA with 11-bit dictionary: 122,632,567 bytes
    LZWA with 09-bit dictionary: 123,951,473 bytes
    LZWA with 12-bit dictionary: 124,822,124 bytes
    LZWA with 13-bit dictionary: 126,908,284 bytes
    LZWA with 16-bit dictionary: 128,272,861 bytes
    LZWA with 14-bit dictionary: 128,310,069 bytes
    LZWA with 15-bit dictionary: 128,598,465 bytes


    File 'world95.txt' from SFC (as a text test-file), 2,988,578 bytes:

    LZWA with 16-bit dictionary: 1,189,003 bytes
    LZWA with 15-bit dictionary: 1,304,384 bytes
    LZWA with 14-bit dictionary: 1,421,517 bytes
    LZWA with 13-bit dictionary: 1,544,254 bytes
    LZWA with 12-bit dictionary: 1,665,004 bytes
    LZWA with 11-bit dictionary: 1,769,910 bytes
    LZWA with 10-bit dictionary: 1,914,236 bytes
    LZWA with 09-bit dictionary: 2,176,829 bytes

    Poor compression... I guess time to add non-greedy parsing or some context stuff...

  5. #5
    Guest
    Poor compression... I guess time to add non-greedy parsing or some context stuff...

    I agree!

  6. #6
    Guest
    lzw is a very bad compression type, there is no way to improve it much. you should use lzss with ari. it has faster decompression speed and better compression ratio. look at lzma,winrk-rolz and others

  7. #7
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    I know about this!
    But sometimes we must experiment with different things.

  8. #8
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    <u> </u>

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