Question for photographers - light fall off

Discussion in 'Photoshop Tutorials' started by Steve Hoffmann, Oct 31, 2003.

  1. I had a chance to play with Photoshop CS and the new Camera Raw program has
    a very nifty tool for controlling vignetting or light fall off in the
    corners of a photographic image. Unfortunately, this tool only works with
    RAW file formats. This phenomenon becomes very apparent in large format
    photography with wide angle lenses. I've been trying to figure out a way to
    use the gradient tool to eliminate the dark corners of my scans. I've come
    close to getting the effect I want but I was wondering if any of you
    photographer/Photoshop users have figured out a good routine with the
    gradient tool to eliminate light fall off (vignetting) in the corners of
    your scans. TIA!!!

    Steve
     
    Steve Hoffmann, Oct 31, 2003
    #1
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  2. Steve Hoffmann

    jjs Guest

    I'll be watching for the definitive answer which _works_, but nothing, but
    nothing I've tried suits my critical requisites. The task concerns more
    than simply applying a graduated filter-effect. The contrast has to change
    accordingly, and not necessarily in a linear manner. Underexpose the
    edges, or overexpose the center... not a good thing. (I'm still looking
    for the proper graduated ND for one particular lens. They are not all
    equal.)
     
    jjs, Nov 1, 2003
    #2
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  3. SNIP
    A simple radial gradient (e.g. layer in Overlay blending mode) is probably
    not accurate enough, but adding a curves correction to it should allow to
    come close. Adding some noise will reduce posterization in 8-bit/channel
    images.

    Alternatively one of the Panorama Tools plug-ins could assist, but that is a
    trial and error process (http://www.tawbaware.com/maxlyons/pano12ml.htm).

    Bart
     
    Bart van der Wolf, Nov 1, 2003
    #3
  4. Steve Hoffmann

    Tacit Guest

    I've been trying to figure out a way to
    You're using the wrong tool for the job.

    Select the corners, either by using a radial gradient in Quick Mask mode, or by
    making a heavily feathered oval selection and inverting it. Then, correct the
    underexposure with Image->Adjust->Curves.
     
    Tacit, Nov 1, 2003
    #4
  5. Slight vignetting is not hard to deal with, but severe cases are much more
    challenging. I don't have to deal with very bad vignetting myself, but even
    so, you have to take care to avoid banding effects. I've described my
    method here:
    http://homepage.ntlworld.com/j.houghton/vignette.htm

    John
     
    John Houghton, Nov 1, 2003
    #5
  6. I have a tip on my web site for a way to deal with this. It even works
    with 16 bit images (although it's a bit convoluted). One of things I
    find that helps is to shoot negative film and give the recommended
    exposure to the corners and allow the center to become overexposed.
    The latitude of the film will handle this and there is not as much
    problem with low contrast in the corners.

    Look under the tips section on my home page.
     
    Robert D Feinman, Nov 1, 2003
    #6
  7. Steve Hoffmann

    PR Guest

    Steve (jjs), I'm looking for a challenge for my next graphics program.

    Please send me details of exactly what sort of plugin/program would
    help you do this at throwaway(at)ransen.com....
     
    PR, Nov 2, 2003
    #7
  8. Steve Hoffmann

    jjs Guest

    Do you want original negatives to work with? I can give you various
    samples, from images with _gross_ (unmitigated ugly) fall-off to the
    'norm' to very slight. (eg; early 47mm Super Angulon on 4x5", the same on
    6x9cm, and 'blad SWC images.)
     
    jjs, Nov 2, 2003
    #8
  9. Panorama Tools includes a tool to deal with this.

    <http://www.path.unimelb.edu.au/~dersch/>
    <http://home.no.net/dmaurer/~dersch/Index.htm>
     
    Stephen H. Westin, Nov 3, 2003
    #9
  10. Thanks for all the useful suggestions!! The problems with some of them is
    that you don't necessarily need the same amount of correction for each
    corner. If you've moved the LF lens for rise fall, shift or tilt even a tiny
    amount, or if the composition is 'just so', you may need slightly different
    corrections for each corner of the image. Here's the best quick and dirty I
    could come up with....

    http://www.sphoto.com/techinfo/wdtech.html#Gradient

    Thanks again for all the helpful suggestions....
     
    Steve Hoffmann, Nov 6, 2003
    #10
  11. Steve Hoffmann

    jjs Guest

    Quick and clean is buying the correct graduated filter for your lens.
    There's no other way. Do it right.
     
    jjs, Nov 6, 2003
    #11
  12. I would if I were positive I'd get perfectly even exposure from center to
    edge. And, I may end up going that route. You said yourself you were still
    looking for the 'proper' ND filter for one of your lenses. At $200+ per
    filter, experimentation would be expensive....:^)
     
    Steve Hoffmann, Nov 6, 2003
    #12
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