Cast removal in small areas

Discussion in 'Photoshop' started by JME3372, Aug 13, 2003.

  1. JME3372

    JME3372 Guest

    After editing a complete image, there are a few small areas left that
    have unwanted casts in them. Without making a selection, are there ways
    to turn these areas into neutral? Thanks.
    JME3372, Aug 13, 2003
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  2. No.
    See my tip on removing the bluish cast in shadows taken under open sky for one
    technique. It would work for any color cast problems.
    Robert Feinman, Aug 13, 2003
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  3. JME3372

    Warren Sarle Guest

    It depends on how the color variation within these small areas overlaps
    with the color variation in the rest of the image. If you're lucky, you
    might be able to use curves, HSB, blending, etc. By far the best
    reference for this sort of thing is Dan Margulis's book, Professional
    Warren Sarle, Aug 13, 2003
  4. JME3372

    Mike Russell Guest

    It is certainly possible, and is done all the time.

    For example, in Lab mode you may be able to zero out the color and reduce or
    eliminate the cast.

    You may be able to convert to CMYK mode, with a heavy or max GCR setting,
    remove the particular cast, and then convert back to RGB. Or selective
    color might get the job done.

    Although you specified no use of masks, which is good. Another related
    approach, similar to masking, would be to dup the layer, correct only areas
    affected by the color cast, and then use the layer blending options to
    select only part of the image.

    At the end of the day, there are some mixed lighting situations that may
    require masking, though the mask may be derived from the image, for example
    by sharply curving the a or b channel, rather than created by hand.

    We love a challenge, why not post your image and see if anyone takes a crack
    at fixing it?


    Mike Russell
    Mike Russell, Aug 14, 2003
  5. JME3372

    JME3372 Guest

    The color variation within these small areas do overlap with the color
    variation in the rest of the image. Without making a selection, I can't
    remove the cast without also influencing the rest of the image.
    Margulis' book is very helpful in many situations, and I reference it
    often. However, without a more detailed step by step tutorial, I find
    his suggestions on how to use curves and blending rather difficult to
    apply in some situations and at my level.

    For example. He chooses and edits the black channel as the blending
    source for a lemon. But the black channel is hardly the obvious choice
    at first sight. How did he make that choice?

    I also have difficulties with images that should end up with no neutral
    white or black points, or with a certain cast. How do I maximize the
    highlights and shadows without pushing them to neutrals?

    I'll see if I can post an example as suggested by Mike.
    JME3372, Aug 14, 2003
  6. JME3372

    JME3372 Guest

    Can I do this blending without making a selection?
    I'm OK when making selections that are rather distinct, but shaky with
    those with a more murky edges.
    See my response to Warren. I'll see if I can post an example. TIA.
    JME3372, Aug 14, 2003
  7. JME3372

    Mike Russell Guest

    Mike Russell wrote:
    [re removing a cast from part of an image]
    yes - double click on the layer name in the layers palette and there will be
    sliders that allow you to determine when the upper layer preempts the lower

    You are right on track, though, in trying to do this without using a
    selection, and I would not resort to layer blending until you had already
    tried normal curve manipulations.


    Mike Russell
    Mike Russell, Aug 14, 2003
  8. JME3372

    Warren Sarle Guest

    Mike should have said, "post your image on your web site, or in an
    alt.binaries.* newsgroup." People who have to pay according to the
    size of stuff they download don't appreciate such large posts.

    I take it the main thing you are trying to do is make the background
    cyan, to contrast with all parts of the flowers. There are, of course,
    many ways to do this. Perhaps the simplest would be to lower the
    shadow part of the curve for the red channel. You can do this without
    altering the flowers by putting 3 or 4 knots in the middle of the red
    curve to nail it down. This gives you a dark cyan background.

    A more flexible way would be to select the background using the
    red channel, which has good contrast between the background and
    the flowers. Open the channels palette and duplicate the red
    channel. Click on the red copy, then use curves to increase the
    contrast until the flowers are solid white and the background is
    very dark (it does't have to be solid black). Then go to the selection
    menu, choose "Load Selection", and load the red copy, inverted.
    This gave me a good selection when I did it on your raw image.
    The little green branch might be a problem, in which case you
    use a different channel to select the branch and subtract that from
    the selection of the background.

    Once you have the background selected, I would say the easiest
    way to change it to cyan would be an adjustment layer using
    color balance.
    Warren Sarle, Aug 15, 2003
  9. JME3372

    nemo Guest

    Sponge tool set to Desaturate.
    nemo, Aug 15, 2003
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