Color Correction (theory question?)

Discussion in 'Photoshop Tutorials' started by jjs, Dec 19, 2003.

  1. jjs

    jjs Guest

    I could use a jump-start here. Call me in dire need of a clue. It has been
    mentioned a few times that one should use curves to correct color, but I
    don't recall the details. How, exactly, does changing a curve change
    color? Yep, I'm stuck in the misconception that curves changes contrast.

    tia
     
    jjs, Dec 19, 2003
    #1
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  2. jjs

    Bill Hilton Guest

    From: (jjs)
    Run the curve on one of the channels instead of on the composite. Then you'll
    see a color change, and if you're watching the RGB values (set up a color
    measurement point in the Info palette) you can change it with a great deal of
    precision.

    Some really smart guys do ALL their color correction with curves, to the point
    they feel us mere mortals who sometimes go slumming and use Levels or Hue/Sat
    or some other wimpy tool must be girly-men when it comes to Photoshop. Dan
    Margulis comes to mind ...

    Bill
     
    Bill Hilton, Dec 19, 2003
    #2
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  3. jjs

    Tacit Guest

    How, exactly, does changing a curve change
    Open your Curves dialog. At the top, you will see a popup menu that says "CMYK"
    or "RGB" (depending on which color mode your image is using). Changing the
    curve at this point will change the overall contrast, or change the overall
    lightness or darkness, or change lightness, darkness, or contrast in localized
    tonal areas, depending on what you do.

    Now, click on the popup menu. You will have the choice to select each color
    channel individually. This is how you perform color correction.

    By changing the curve in each channel, you can change the color balance of the
    entire image, or change the color balance of localized tonal areas.

    For example, let us suppose you have a CMYK image which was shot under
    flourescent light. It's greenish. To change the colorbalance, you would open
    the Curves dialog, then in the Magenta channel, add magenta to the midtones and
    shadows. Depending on the nature of the color cast,y ou might also remove Cyan
    selectively from the hilights and midtones.

    If you have an RGB image that is too red in the shadows, you would open the
    Curves dialog, go to the Red channel, and subtract red from the shadows; it
    might also be beneficial to boost density in the shadows by adding green and
    blue.

    Curves is your best first line of approach for color correction; it allows you
    to make both obvious and subtle changes to the color of all or part of your
    image. It does far, far more than just change contrast.
     
    Tacit, Dec 19, 2003
    #3
  4. jjs

    jjs Guest

    Tacit said in part.
    You read my mind. Yep, I've got a shot with corrupted color due to the
    fact that some of the flourescents were not daylight. They were _supposed_
    to be daylight, but the maintenance crew had their way, didn't follow the
    book. A friggin shame of thing to do to a gallery. (I'm going to have to
    buy a color meter.)

    [... snipped the most excellent post - see it ...]

    Thank you Bill and Tacit. Tacit, your explanation was particularly
    generous and perfectly clear. I owe you one.
     
    jjs, Dec 19, 2003
    #4
  5. jjs

    jjs Guest

    Channels! Of course. (slapping my dim brain)
    Girly-men? LOL! I hear that pink frilly panties are included with
    Elements. True?
     
    jjs, Dec 19, 2003
    #5
  6. jjs

    Flycaster Guest

    Jeez, "slumming girly-men", eh? Well, I've been called worse...
     
    Flycaster, Dec 19, 2003
    #6
  7. jjs

    Farlo Guest

    I've BEEN worse ... =;>
     
    Farlo, Dec 19, 2003
    #7
  8. jjs

    Mike Russell Guest

    Here's a new PS plugin that takes a new look at curves, including shadow,
    highlight, and neutrals, as well as color spaces that you may find
    interesting: www.curvemeister.com
     
    Mike Russell, Dec 21, 2003
    #8
  9. jjs

    jjs Guest

    Many thanks, Master Russell!
     
    jjs, Dec 21, 2003
    #9
  10. jjs

    Warren Sarle Guest

    How does this differ from using the black, gray, and white eyedroppers
    in the Levels and Curves commands?
     
    Warren Sarle, Dec 21, 2003
    #10
  11. jjs

    Mike Russell Guest

    In several ways. Two important ones are that the shadow, highlight, and
    neutral points are carried over to the other color spaces, so the work you
    do in RGB modifies the Lab, wg-CMYK, and HSB curves as well. You can also
    drag around the highlight and shadow points after the fact to fine tune
    them.

    The curvemeister demo is fully functional, so you can check out all these
    features, and run through the tutorials.
     
    Mike Russell, Dec 21, 2003
    #11
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