Apple Color 1.0 - Manual (Page 199)

Chapter 9 Primary In 199
This operation certainly neutralizes the red in the shadows; unfortunately, because this
one control point is influencing the entire curve, this correction also removes much of
the original red from the midtones as well.
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Tip: If you’re wondering where you should place control points on a curve to make an
alteration to a specific area of the image, you can use the height of the corresponding
graphs in the Waveform monitor set to either Parade (if you’re adjusting color) or Luma
(if you’re adjusting the Luma curve). For example, if you want to adjust the highlights of
the image, you’ll probably need to place a control point in the curve at approximately
the same height at which the highlights appear in the waveform graph.
2 Add another control point near the top of the red curve, and drag it up until some red
“fill” reappears on the side of the woman’s face.
This adds the red back to the woman’s face, but now you’ve added red to the
highlights of the key light source, as well.