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Resolution setting in a bitmap file - Macromedia Fireworks

When I export a 300ppi (=11811 px/m) image from Fireworks (version 4) as a bitmap, the resolution written into the file header is 11808 px/m. There is a similar discrepancy at all resolutions and Photoshop 6 shows the same behaviour. No one in comp.graphics.apps.photoshop or macromedia.director.lingo will tell me why :-( Please, please, please will someone tell me where the discrepancy comes from in detail so that I can reproduce it? Andrew Morton...

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  1. #1

    Default Resolution setting in a bitmap file

    When I export a 300ppi (=11811 px/m) image from Fireworks (version 4) as a
    bitmap, the resolution written into the file header is 11808 px/m. There is a
    similar discrepancy at all resolutions and Photoshop 6 shows the same behaviour.
    No one in comp.graphics.apps.photoshop or macromedia.director.lingo will tell me
    why :-(
    Please, please, please will someone tell me where the discrepancy comes from in
    detail so that I can reproduce it?

    Andrew Morton

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    Andrew Guest

  2. #2

    Default Re: Resolution setting in a bitmap file


    "Andrew Morton" <co.uk.invalid> wrote in message
    news:bvqk5i$lbk$macromedia.com... 
    is a 
    behaviour. 
    tell me 
    from in 

    Interesting. What bitmap format are you using, precisely?

    Anyway, I don't think that 0.025% error will somehow affect real print
    output. Actually, as long as I understand, the difference between
    traditional US/UK and European point systems is larger, yet it didn't kill
    anyone.

    Ilyich.
    --------------------------------------------------------------------------
    Ilya Razmanov (a.k.a. Ilyich the Toad)
    http://photoshop.msk.ru/ - Photoshop plug-in filters
    "How did I get into this mess? I really don't know how. We
    seem to be made to suffer. It's our lot in life." - C3PO, Star Wars
    --------------------------------------------------------------------------


    Ilya Guest

  3. #3

    Default Re: Resolution setting in a bitmap file

    > Interesting. What bitmap format are you using, precisely?

    http://msdn.microsoft.com/library/default.asp?url=/library/en-us/gdi/bitmaps_1rw2.asp

    To convert from ppi to px/m I multiply by 39.37 in/m
    (http://physics.nist.gov/Pubs/SP811/appenB.html).
     

    What I'm doing is using Director to generate pages to be printed; the user can
    choose the resolution to generate the page at so if they use Photoshop they
    might be upset to find that the resolution doesn't appear to be quite what they
    asked for.
     

    I think you're referring to traditional typesetting points (72.27 per inch) as
    opposed to computer points (72 per inch) which doesn't really apply in this
    case.

    Andrew

    Andrew Guest

  4. #4

    Default Re: Resolution setting in a bitmap file


    "Andrew Morton" <co.uk.invalid> wrote in message
    news:bvqroo$36q$macromedia.com... 
    >
    >[/ref]
    http://msdn.microsoft.com/library/default.asp?url=/library/en-us/gdi/bitmaps_1rw2.asp 

    Stgangely enough, I cannot access the doent. Will try again later. What
    is interesting, as long as I remember currently UK inch is 2.54 cm exactly
    (that seem to give the difference close to that you mentioned). I don't
    remember about how US inch may have changed over time.
     
    >
    > What I'm doing is using Director to generate pages to be printed; the user[/ref]
    can 
    they 
    they 

    I understand. But try to calculate the result of such an error for, say, A4
    page. I *seriously* doubt anybody will notice that difference when the image
    gets printed.

    So far, I may only guess what may be the reason for the problem. Roundoff
    errors during meter\inch conversion? Different meter values for inch?
     [/ref]
    kill 
    >
    > I think you're referring to traditional typesetting points (72.27 per[/ref]
    inch) as 
    this 

    Nope. I'm referring to the fact that 1 point (traditional) in US and 1 point
    (traditional) in Russia have different sizes due to different meter value
    for inch being used for calculation. Still, nobody notice that when reading
    the book :-)

    Ilyich.
    --------------------------------------------------------------------------
    Ilya Razmanov (a.k.a. Ilyich the Toad)
    http://photoshop.msk.ru/ - Photoshop plug-in filters
    "How did I get into this mess? I really don't know how. We
    seem to be made to suffer. It's our lot in life." - C3PO, Star Wars
    --------------------------------------------------------------------------


    Ilya Guest

  5. #5

    Default Re: Resolution setting in a bitmap file

    It turns out that pretending there are 39.36096 in/m gives the Photoshop answer.
    Thanks to boa! in m.d.l.

    Andrew

    Andrew Guest

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