settings for scanning 35mm negatives

Discussion in 'Scanners' started by Louise, Jul 10, 2005.

  1. Louise

    Louise Guest

    Epson 2400 with film holder. P4, 3.2 with 2 gig of ram and 75 gig free
    on hard drive.

    Using Epson software - twain.

    I would like to scan a 35mm negative at the highest resolution and color
    depth possible so that when I work with it in Photoshop, I can get the
    best possible quality.

    My work will often involve extensive cropping and therefore, the final
    photo will be only a small portion of the entire negative.

    The Epson software gives me the option to scan as high as 48 bit and to
    at a resolution of 12800. But when I try to actually scan at this high
    end, my computer freezes although it "should" have enough power.

    I seem to need to go down to 24 bit and either 4800 or 2400 resolution
    for it to successfully save a scan.

    Why can't I use the higher settings?

    And, what would be reasonable settings to use to achieve good quality?
    Do I need to scan at such a high bit rate and resolution?

    TIA

    Louise
     
    Louise, Jul 10, 2005
    #1
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  2. A couple of reasons.

    Firstly, at 12800ppi and 48bit resolution, the entire image occupies at
    least 1.3Gb of RAM. Windows itself occupies a fair bit, as well as the
    TWAIN interface and applications, so perhaps there just isn't enough
    memory to hold the entire file. The Epson TWAIN driver stores the image
    temporarily in real RAM, rather that writing it to disk, so hardware is
    sometimes a limitation, particularly if several frames are selected at
    once.

    There have been a couple of reports that the Epson driver encounters
    problems with more than 2^30 bytes in the image, which is 1Gb - your
    file is larger than this.

    Are there any settings between 4800ppi/8bpc and 12800ppi/16bpc that
    work? You might find the point that it falls over is just marginally
    short of what you are trying.
    No, you don't need to scan at such high resolution. More importantly,
    there is no advantage whatsoever in doing so. Your scanner has a
    nominal resolution of 2400ppi. By half stepping the stepper motor it
    can achieve 4800ppi in one axis, whilst interpolating the other axis to
    get 4800ppi in that as well. Beyond 4800ppi everything, in both axes,
    is interpolated - data invented by the software based on mathematical
    rules applied to the real data. In practical terms, the maximum useful
    resolution is 2400ppi, and even at that the contrast at the resolution
    limit is negligible, so it is generally a complete waste of time using
    anything more.

    Whether you scan at 48-bit colour or 24-bit colour depends on how much
    post processing you intend to do on the resulting image. You cannot
    even see a full 24-bit colour range, let alone print it. But as much
    overhead as possible is always useful if you intend to apply significant
    alterations to the gamma and contrast of the image. Otherwise 24-bits
    is more than adequate for almost all applications.

    In fact, there is an outstanding challenge, which has never yet been
    met, to produce an image using 48-bit scanning which could not equally
    be achieved with 24-bit scanning and appropriate common sense in setting
    the controls of the scanner.

    So, for most of your purposes, the best you will get out of your scanner
    will no be limited in any way by scanning at 2400ppi and 24-bit colour,
    yielding a maximum image from a 35mm frame of about 3400x2268 pixels and
    a file size of 23Mb - which your computer will handle very nicely.
     
    Kennedy McEwen, Jul 11, 2005
    #2
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  3. Louise

    Louise Guest

    Thanks so much for the helpful description of what's "really" happening.

    By shutting down almost all other running programs, I can - if I wish to
    - go to 48bit by 4800 resolution saved as a tiff, although it takes a
    while.

    But my question now is: if I use 4800ppi, one axis is being
    interpolated. Am I doing my photograph any favor at all by doing this?
    Am I enhancing the final image (which I plan to adjust in Photoshop), or
    am I filling my image with "interpolation" rather than quality?

    Also, am I better off with tiff or psd since I plan to work with it in
    Photoshop?

    Thanks again.

    Louise
     
    Louise, Jul 11, 2005
    #3
  4. The answer to that is in the part of above paragraph that you snipped:
    "In practical terms, the maximum useful resolution is 2400ppi, and even
    at that the contrast at the resolution limit is negligible, so it is
    generally a complete waste of time using anything more."
    There is some minor benefit to scanning at 4800ppi in that you are
    collecting twice as many real data samples and thus improving the signal
    to noise ratio of the scan in the same way as 2x multiscanning on a
    dedicated film scanner. However you are unlikely to see any discernable
    resolution difference. Interpolation actually produces a desharpening
    effect, and the interpolation in one axis more than offsets the improved
    resolution in the other.

    There is little difference for the scanned image and both formats are
    losslessly compressed. Tiff files are more portable, but psd is a useful
    intermediary format that will allow you to save all the Photoshop layers
    and their interactions should you wish to change your edits in future.
    However, when used in this way, psd files can become enormous. I would
    recommend tiff formats in general unless you really need the options
    that the psd offers.
     
    Kennedy McEwen, Jul 11, 2005
    #4
  5. Louise

    Louise Guest

    Thanks - very helpful links.

    Louise
     
    Louise, Jul 12, 2005
    #5
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