Ideal characteristic curve for digital printing

Discussion in 'Digital Photography' started by Marc Wossner, Apr 12, 2008.

  1. Marc Wossner

    Marc Wossner Guest

    Dear ng,

    the combination of the negative and positive charakteristik curves in
    analog photography leads to the well known s-shaped curve of the final
    print. The main reason for this characteristic is to compensate for
    flare light. Camera flare and viewing flare lowers gamma mostly in the
    dark tones and printer flare mostly in the light tones. So the gamma
    of the photographic system must be raised a lot at the high desities
    and a bit less at the low densities.
    As there is no optical enlarging step in digital printing an ideal
    characteristic curve for an image prepared to be printed on an inkjet
    should have a different characteristic than this. - Of course it must
    still care not to blow out the highlights, so ist should still be
    somewhat rounded. Any thoughts or references about that?

    Best regards!
    Marc Wossner
     
    Marc Wossner, Apr 12, 2008
    #1
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  2. I don't believe the main reason for the bends in the curve were to do
    with flare. There were films with a quite straight curve, and ones
    that were very S shaped. I believe the rounding of the ends (either a
    lot or a little) were somewhat inherent in the chemical processes.

    One could modify the curves by chemistry. The curve published in the
    mfg's catalog was with a certain developer and concentration and time.
    One could use a different developer, a different dilution, or a
    different developing time. Of course, you also could use a modified
    curve again when printing.

    One of the first things I marveled at in digital processing was how I
    could take an existing image and bend the curve around on the
    computer, and put it back if I made a mistake. In the olden days to
    change the curve on a negative after the fact meant reshooting :-(
     
    Don Stauffer in Minnesota, Apr 12, 2008
    #2
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  3. Marc Wossner

    Marc Wossner Guest

    You are of course right, I should have written that the characteristic
    of the final print must be somewhat curved or bent to accomodate the
    different gammas required to compensate for the different amounts of
    flare in the highlights and in the shadows as can be seen in the The
    Focal Encyclopedia of Photography (http://books.google.de/books?
    id=CU7-2ZLGFpYC&pg=PA148&lpg=PA148&dq=%22viewing+flare
    %22+gamma&source=web&ots=d8tQGLXtfr&sig=8sI7ELK8w9megD7pGtnm6qvt7FY&hl=de
    page 146 top left).

    But anyway, what about the fact that there is no optical enlarging
    stage in digital imaging. How should that affect the characteristic of
    the final print as far as the highlight part is concerned?

    Marc Wossner
     
    Marc Wossner, Apr 12, 2008
    #3
  4. Fortunately, the dynamic range of digital cameras far exceeds the
    dynamic range of printing papers. Thus using the curve tool in a good
    image editor works fine. But there IS no rule about the preferred
    shape. Each image is unique. If the original scene has a wide dynamic
    range you must compensate somehow. However, it if is a flat, low key
    scene you can use quite a linear shape.

    One of the neatest aids recently has been the HDR software, either
    special program or built into things like PS CS2 and 3, or the latest
    version of PSP. This GREATLY eases the computer work for high range
    scenes, though at the expense of needing to shoot multiple exposures.
     
    Don Stauffer in Minnesota, Apr 13, 2008
    #4
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