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Thread: DPI to file size question - pls help

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    Supreme Member Flop21's Avatar
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    DPI to file size question - pls help

    "An image scanned at 600 dpi has an image size of 16 MB. What would be the expected file size if it was rescanned at 300 dpi?"

    I thought I could just go, x/300 = 16/600, thus x = 8 MB. But that's wrong.


    The answer is 4 MB... but how?


    This is an industrial technology multimedia question, but hoping someone can help me out even if they don't do the subject.


    [Also if math isn't even mentioned in the syllabus, why is this a HSC question? DPI also is not in the syllabus, colour depth and binary digits are though - but as far as I know... DPI does not equal colour depth right?]
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    The pessimistic optimist. BLIT2014's Avatar
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    Re: DPI to file size question - pls help

    Well first of 600DPI, is 600*600 (Square)

    That means if you change it to 300DPI, it is 300*300 (Square)

    (300*300)/(600*600)=1/4

    Therefore, if 600DPI has an image size of 16MB, as it the other image has 1/4 of the information.

    You would go 16 * 1/4 =4MB
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    Supreme Member Flop21's Avatar
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    Re: DPI to file size question - pls help

    Quote Originally Posted by BLIT2014 View Post
    Well first of 600DPI, is 600*600 (Square)

    That means if you change it to 300DPI, it is 300*300 (Square)

    (300*300)/(600*600)=1/4

    Therefore, if 600DPI has an image size of 16MB, as it the other image has 1/4 of the information.

    You would go 16 * 1/4 =4MB
    Ohhhh, right. I was thinking the DPI was already a square, but it's not.

    Thanks!
    2015 HSC: English Adv, Mathematics, Business Studies, Biology, Multimedia.

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