Curves: white eyedropper corrects overall contrast - sometimes!

Discussion in 'Digital Photography' started by denis@boisclair.freeserve.co.uk, Feb 4, 2005.

  1. Guest

    I am working hard to familiarise myself with Curves in Photoshop!

    I have found that with some photos, clicking the light eyedropper on a
    white object in the photo makes the whole picture 'spring to life' with
    a nicely brightened picture and overall well adjusted contrast. I wish
    it could always be as easy as that and I don't understand why it only
    works for a minority of photos.

    On most photos I pick 3/4 spots on the graph and have to use trial and
    error to achieve a satisfactory result.Use of the 'Brightness/Contrast'
    controls seems to be frowned on by experts but sometimes I find this
    useful for 'tweaking', when the general contrast balance looks OK but a
    slight boost in contrast is still needed.


    Can anyone explain the strange'eyedropper' behaviour please ?

    Denis Boisclair
    Cheshire,England.
     
    , Feb 4, 2005
    #1
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  2. JC Dill Guest

    On 4 Feb 2005 02:40:45 -0800, wrote:

    >I am working hard to familiarise myself with Curves in Photoshop!
    >
    >I have found that with some photos, clicking the light eyedropper on a
    >white object in the photo makes the whole picture 'spring to life' with
    >a nicely brightened picture and overall well adjusted contrast.


    Before you use curves, try using levels. Create an adjustment layer
    for levels, and move the edge pointers to the edge of the histogram.
    Then move the center pointer (if needed) to bring out the center
    values in your image. Only AFTER you have adjusted the levels should
    you then use curves.

    Another trick is to use a temporary "threshold layer" to find the
    whitest and blackest spots in your image and mark them, and then use
    those points for setting the edges of your curves settings using the
    eyedropper. (I do this *after* setting the levels, YMMV.) See Scott
    Kelby's _Photoshop for Digital Photographers_ for this tip, and many
    others. He has 2 editions of this book for PS7 and for CS so you can
    get the right edition for your program.

    jc
     
    JC Dill, Feb 4, 2005
    #2
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  3. Chris Myers Guest

    Re: Curves: white eyedropper corrects overall contrast -sometimes!

    On 2/4/05 6:07 AM, in article ,
    "JC Dill" <> wrote:

    > On 4 Feb 2005 02:40:45 -0800, wrote:
    >
    >> I am working hard to familiarise myself with Curves in Photoshop!
    >>
    >> I have found that with some photos, clicking the light eyedropper on a
    >> white object in the photo makes the whole picture 'spring to life' with
    >> a nicely brightened picture and overall well adjusted contrast.

    >
    > Before you use curves, try using levels. Create an adjustment layer
    > for levels, and move the edge pointers to the edge of the histogram.
    > Then move the center pointer (if needed) to bring out the center
    > values in your image. Only AFTER you have adjusted the levels should
    > you then use curves.
    >
    > jc
    >

    Another tool to use in levels is to hold down the Option [Mac] or Alt [PC]
    key and move the white and black sliders in and out. Moving the white will
    turn the image completely black but show you the areas that would be blown
    out, the black will turn the image white and the areas of solid black will
    be colored. When you release the keys, you'll be back to the normal
    appearance of the image but with the corrections you made.

    CM
     
    Chris Myers, Feb 4, 2005
    #3
  4. paul Guest

    wrote:
    > I am working hard to familiarise myself with Curves in Photoshop!
    >
    > I have found that with some photos, clicking the light eyedropper on a
    > white object in the photo makes the whole picture 'spring to life' with
    > a nicely brightened picture and overall well adjusted contrast. I wish
    > it could always be as easy as that and I don't understand why it only
    > works for a minority of photos.
    >
    > On most photos I pick 3/4 spots on the graph and have to use trial and
    > error to achieve a satisfactory result.Use of the 'Brightness/Contrast'
    > controls seems to be frowned on by experts but sometimes I find this
    > useful for 'tweaking', when the general contrast balance looks OK but a
    > slight boost in contrast is still needed.
    >
    >
    > Can anyone explain the strange'eyedropper' behaviour please ?



    Here's my understanding. No warranty as to flawless knowledge.

    The eyedropper is used to click on what you know to be neutral gray,
    white or black areas to correct the color balance. After doing that,
    drop the channel:RGB list & see what it has done to the curves of the
    individual colors.

    Click the Options button to have a little more control over the same
    effect as the Auto button & change the highlight shadow numbers for more
    contrast then check the individual channels & note that the lines are
    straight not curved. That means this is more like a levels adjustment
    and is done by discarding highs and lows.

    Curves are a little more subtle about preserving the highs and lows
    while adjusting the range between, more like adjusting the middle slider
    in a levels adjustment but with more control to add multiple points
    along the curve and make custom "s" shapes. You can pull the darkest
    shadows down a bit then hold the eyedropper over the part of the image
    you want to have more contrast & see that on the curve to know where you
    want to steepen the curve then add another point to round it off beyond
    there so the highlights don't go too far.

    Adjusting the high & low ends in the levels tool is more like dragging
    the endpoints on the curves tool and making straight lines discarding
    the ends. The eyedropper in the levels tool does something similar to
    ato correction in the curves tool but the eyedropper in the curves tool
    has a more subtle curved impact.

    But to answer your question, the eyedropper is intended for color
    correction more than contrast. If the color is OK you can make your own
    curve in the RGB composite for contrast or use levels in the RGB composite.
     
    paul, Feb 4, 2005
    #4
  5. Frank ess Guest

    wrote:
    > I am working hard to familiarise myself with Curves in Photoshop!
    >
    > I have found that with some photos, clicking the light eyedropper on a
    > white object in the photo makes the whole picture 'spring to life'
    > with a nicely brightened picture and overall well adjusted contrast.
    > I wish it could always be as easy as that and I don't understand why
    > it only works for a minority of photos.
    >
    > On most photos I pick 3/4 spots on the graph and have to use trial and
    > error to achieve a satisfactory result.Use of the
    > 'Brightness/Contrast' controls seems to be frowned on by experts but
    > sometimes I find this useful for 'tweaking', when the general
    > contrast balance looks OK but a slight boost in contrast is still
    > needed.
    >
    >
    > Can anyone explain the strange'eyedropper' behaviour please ?
    >
    > Denis Boisclair
    > Cheshire,England.


    I understand the resolution on your screen has an effect on the reaction
    of Curves when you select a white (or other) point. At fit-on-screen
    size, your selection is likely to include a range of points, influencing
    what Curves sees as its reference for changes. A small shift of the
    cursor may have a large effect of what your image looks like. At
    really-big size, you can select a (perhaps) narrower range, resulting in
    a different action by Curves.

    Also, selection of a white point is better restricted to
    not-really-completely-whites (white clouds with some shading, as opposed
    to specular reflections, the example I remember).

    As others have mentioned, it seems Levels shouild come first, and may
    eliminate the need to try Curves as a generator of "Pop". One authority
    teaches to set the end-of-histo points and then move the gray indicator
    to taste. He went on to say many, if not most of the images he sees need
    the gray moved to +1.5 to begin ! Mine are more in the neighborhood of
    +1.25 - 1.30. Eyes differ.


    --
    Frank ess
     
    Frank ess, Feb 4, 2005
    #5
  6. Guest

    Curves: white eyedropper corrects overall contrast - sometimes!

    I am again indebted to Forum members for not only a very fast response
    but for some rerally useful advice. I will certainly make surteb that I
    master Levels before moving on to Curves.

    I have printed out your replies for reference!

    My thanks to all concerned.

    Denis Boisclair
    Cheshire, England
     
    , Feb 5, 2005
    #6
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