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Thread: Best compresson - ISO

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    Question Best compresson - ISO

    Hello all,

    Does anyone know what is best compression technique for compressing ISO type of files(which contain installation media). I have tried using 7z & peazip tools.

    However i could not try all the algorithms. Like, the PAQ8* method wont work in peazip when i try to compress my ISO files.
    Can anyone please share their experience as to which algorithm is best & the technique.

    Thanks!

    .

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    Programmer schnaader's Avatar
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    Its very likely that Precomp will help you. Use it like this:

    Code:
    precomp -c- -intense filename.iso
    (If it takes too long, try it without the intense switch)

    The output will be a file named filename.pcf. Precomp will display some statistics - if it finds streams and the file gets larger, you can compress this PCF file instead of the original ISO file to get better results. Restore the original file using

    Code:
    precomp -r filename.pcf
    Additionally, have a look at SREP - using a "tool chain" like Precomp->SREP->7-Zip usually gives good results with fast decompression.
    Last edited by schnaader; 3rd October 2011 at 13:43.
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    Member Surfer's Avatar
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    i tried
    precomp -c- -intense filename.iso

    To test i tried a smaller file size, 550mb. It ran quickly to generate a higher size file. 561mb.
    (it did generate summary of details of objects in the original file.& also, options to use for better compress)

    Then, i tried a 650mb file. It took considerably longer. And stopped working at 97.25% progress.

    Update:
    tried precomp on 4GB iso, it stopped working at 12%

    btw, precomp is not compressing in all above cases,
    Original -- Processesed -- ProcessedFileSize
    550mb 100% 561mb
    650mb 97.5% 1.9GB
    4GB 12% 503mb
    Last edited by obi1; 4th October 2011 at 13:17. Reason: adding to this to avoid double post

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    Programmer schnaader's Avatar
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    Could you elaborate on "stop working"? The activity indicator isn't perfect yet, so don't think it stops just because this one isn't moving. If it's a real crash, though (error dialog popping up), please give it another try adding "-t-j" which disables JPEG recompression that has some stability issues.

    650 MB getting to around 2 GB is very well, Precomp indeed isn't compressing ("-c-" disables built-in bZip2 compression) - as I said, the output is larger, but feeding the PCF file to 7-Zip will lead to a much better result than using 7-Zip on the ISO directly.
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    i see, i misunderstood the function of precomp.

    However, their is no error message. It is a typical application crash. "precomp has stopped working"
    And then i have to choose 'close program'
    Last edited by obi1; 4th October 2011 at 19:50.

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    Programmer schnaader's Avatar
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    Quote Originally Posted by obi1 View Post
    However, their is no error message. It is a typical application crash. "precomp has stopped working"
    And then i have to choose 'close program'
    Yes, it's very likely that this is an error from JPG recompression, so adding "-t-j" should indeed help with this.
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    Quote Originally Posted by schnaader View Post
    Yes, it's very likely that this is an error from JPG recompression, so adding "-t-j" should indeed help with this.
    Yes, -t-j solved the problem. Thanks.

    Also, results after using precomp & srep and then compressing are very good.

    I am now trying out the different compressions available to find which one will be the best.
    paq9a seems to give good results so far. However it is tagged as experimental.
    Is there anything stable and comparable/better to paq9a(with regards to ISO compressing)?

    Thank-you!

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    Programmer schnaader's Avatar
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    Regarding the PAQ "family", for good and still quite fast results, you should have a look at ZPAQ which can take advantages from multi-core processors, too. There's a nice table at the page, too, that gives a rough impression of compression ratio/time compared to 7-Zip (at least for text, but it also processes well on different types of data).
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    NanoZip probably has plenty of filters that would help.

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    zpaq (-m4 -bs) did not compress as good as paq9a (-9)
    And it took more time than paq9a.

    nanozip is also experimental & no update since June 2010. I will give it a try, though.

    Thanks.

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    Yes, paq9a -9 uses 1.6 GB memory, much more than zpaq -m4 (278 MB).

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    Following are results from compression using different programs & algorithms.
    (Content type: Installation media for a linux based distribution)

    710,193,152-->2,045,708,876-->1,602,073,489
    iso------------>pcf------------->srep

    Compressing the srep output:
    - 374,872,306 nz(cc900m)
    - 411,039,607 nz(cO900m)
    - 411,394,229 paq9a(-9)
    - 432,790,658 arc(-mx-ld1600m)
    - 449,958,243 7zip(UltraLZMA2)

    Thanks everyone for your help.
    (If anyone finds or knows a technique to compress much better than above, please post)

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    You can also try StuffIt, but I doubt that anything today can beat NanoZip with reasonable performance.

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    Although nz (commandline) gave good results, currently i would prefer using paq9a.
    For one, paq9a is GPL licensed and secondly, i found it is a very good trade off between compressed output size & time taken.

    What license does nz use?
    Stuffit is completely proprietary. Also, since you say it wont be better than nz, i dont find any point trying it out.

    btw, is there any alternative to precomp, that is released under GPL?

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    Quote Originally Posted by obi1 View Post
    btw, is there any alternative to precomp, that is released under GPL?
    No.

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