Scanned Slides: Filtering non-uniform edge discolorations

Discussion in 'Digital Photography' started by Acecliffy, Sep 15, 2006.

  1. Acecliffy

    Acecliffy Guest

    MY SITUATION: I am scanning color slides that are 20 years old. They
    have edge discoloration, meaning that the sides are somewhat darker
    (perhaps blueish) than the center of the slide. This is not a problem
    with my slide scanner; rather, it is inherent in the slides. I don't
    know why they have this problem, since I am doing this job for my major
    professor.

    So... here is an example of what I am talking aoubt. There is a link
    to a sample image here:
    http://web.ics.purdue.edu/~racz/images/Image012.jpg

    The concrete on the left should have roughly the same color as the
    concrete in the center, but it has a blue tint (I believe, maybe it is
    a mixture).

    MY QUESTION: Is there a filter to adjust/perform color corrections for
    non-uniformity such as this, where a hue/saturation/balance is
    non-uniform across the image? It may be a linear gradient, or perhaps
    even a circular/eliptical gradient?

    Thanks in advance.
    Acecliffy, Sep 15, 2006
    #1
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  2. Acecliffy

    Rutger Guest

    "Acecliffy" <> schreef in bericht
    news:...
    > MY SITUATION: I am scanning color slides that are 20 years old. They
    > have edge discoloration, meaning that the sides are somewhat darker
    > (perhaps blueish) than the center of the slide. This is not a problem
    > with my slide scanner; rather, it is inherent in the slides. I don't
    > know why they have this problem, since I am doing this job for my major
    > professor.
    >
    > So... here is an example of what I am talking aoubt. There is a link
    > to a sample image here:
    > http://web.ics.purdue.edu/~racz/images/Image012.jpg
    >
    > The concrete on the left should have roughly the same color as the
    > concrete in the center, but it has a blue tint (I believe, maybe it is
    > a mixture).
    >
    > MY QUESTION: Is there a filter to adjust/perform color corrections for
    > non-uniformity such as this, where a hue/saturation/balance is
    > non-uniform across the image? It may be a linear gradient, or perhaps
    > even a circular/eliptical gradient?
    >
    > Thanks in advance.
    >


    No problem: in PS, make a rectengular selection with a big feather, invert
    the selection and correct with curves or any other means you like.

    Rutger


    --
    http://www.flickr.com/photos/zwaarddrager/
    Rutger, Sep 15, 2006
    #2
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  3. Acecliffy

    Guest

    + remember that you are looking at a slide... a transparency...
    color fade in the jpg you posted is almost indiscernible. As
    for the color cast, Gimp has numerous plug-ins which will
    correct this.


    Acecliffy wrote:
    > MY SITUATION: I am scanning color slides that are 20 years old. They
    > have edge discoloration, meaning that the sides are somewhat darker
    > (perhaps blueish) than the center of the slide. This is not a problem
    > with my slide scanner; rather, it is inherent in the slides. I don't
    > know why they have this problem, since I am doing this job for my major
    > professor.
    >
    > So... here is an example of what I am talking aoubt. There is a link
    > to a sample image here:
    > http://web.ics.purdue.edu/~racz/images/Image012.jpg
    >
    > The concrete on the left should have roughly the same color as the
    > concrete in the center, but it has a blue tint (I believe, maybe it is
    > a mixture).
    >
    > MY QUESTION: Is there a filter to adjust/perform color corrections for
    > non-uniformity such as this, where a hue/saturation/balance is
    > non-uniform across the image? It may be a linear gradient, or perhaps
    > even a circular/eliptical gradient?
    >
    > Thanks in advance.
    , Sep 15, 2006
    #3
  4. Acecliffy

    Mike Hyndman Guest

    "Acecliffy" <> wrote in message
    news:...
    > MY SITUATION: I am scanning color slides that are 20 years old. They
    > have edge discoloration, meaning that the sides are somewhat darker
    > (perhaps blueish) than the center of the slide. This is not a problem
    > with my slide scanner; rather, it is inherent in the slides. I don't
    > know why they have this problem, since I am doing this job for my major
    > professor.
    >
    > So... here is an example of what I am talking aoubt. There is a link
    > to a sample image here:
    > http://web.ics.purdue.edu/~racz/images/Image012.jpg
    >
    > The concrete on the left should have roughly the same color as the
    > concrete in the center, but it has a blue tint (I believe, maybe it is
    > a mixture).
    >
    > MY QUESTION: Is there a filter to adjust/perform color corrections for
    > non-uniformity such as this, where a hue/saturation/balance is
    > non-uniform across the image? It may be a linear gradient, or perhaps
    > even a circular/eliptical gradient?

    Try this
    Copy the layer and adjust the saturation of the copied layer to lower the
    blue component, then apply a layer mask to this layer and try a radial
    gradient fill on the mask to mask out the overcorrected centre of the top
    layer.

    MH
    Mike Hyndman, Sep 16, 2006
    #4
  5. Acecliffy

    Joal Heagney Guest

    Acecliffy wrote:
    > MY SITUATION: I am scanning color slides that are 20 years old. They
    > have edge discoloration, meaning that the sides are somewhat darker
    > (perhaps blueish) than the center of the slide. This is not a problem
    > with my slide scanner; rather, it is inherent in the slides. I don't
    > know why they have this problem, since I am doing this job for my major
    > professor.
    >
    > So... here is an example of what I am talking aoubt. There is a link
    > to a sample image here:
    > http://web.ics.purdue.edu/~racz/images/Image012.jpg
    >
    > The concrete on the left should have roughly the same color as the
    > concrete in the center, but it has a blue tint (I believe, maybe it is
    > a mixture).
    >
    > MY QUESTION: Is there a filter to adjust/perform color corrections for
    > non-uniformity such as this, where a hue/saturation/balance is
    > non-uniform across the image? It may be a linear gradient, or perhaps
    > even a circular/eliptical gradient?
    >
    > Thanks in advance.
    >


    The problem here is that you need to remove the shadow on the edges,
    without effecting the rest of the image's structure. We need a layer
    that represents the low-frequency hue/saturation/value information of
    the image.

    Here is my hack.

    1. Duplicate the layer.
    2. Hit the duplicate layer with a large Gaussian Blur. I chose a radius
    of 300, as your image was 600 pixels tall. This will wipe out all higher
    frequency structure, leaving a layer that only contains the non-uniform
    hue/saturation/balance information.
    3. I then set the Mode of the top layer to Grain Extract.

    This results in an image of even hue and value. However the image does
    seem to have become somewhat desaturated, and increased brightness. This
    could be fixed by:
    4. Merging the visible layers, and applying Colour/Contrast, Levels or
    Hue/Saturation adjustments.
    5. Desaturating the top layer before you merge the visible layers,
    except that this doesn't get rid of the blueness in the concrete, and
    still results in an increase in overall brightness.

    A final option would be to decrease the brightness of the image BEFORE
    applying steps 1/2/3, or adjust the top layer's brightness/contrast
    after step 3 but before step 4.

    Hope this helps?

    Joal Heagney
    Joal Heagney, Sep 17, 2006
    #5
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