When color correcting an image, there are often specific colors within the image that need to be precisely defined; often these are near white, near black, or gray colors, all of which are relatively easy to color correct; but one color that usually needs to be corrected most precisely is skin tone. Skin tones can be fairly subjective to correct, but there are some strategies you can use to precisely match skin colors (this technique is partially based on steps in Katrin Eismann's book, see the Appendix).
1 Examine the image and make some basic evaluation of the color cast.
Select the color sampler tool. Use it to place a sample point on the subject's skin; use a patch of skin that you will want to be perfectly color balances; avoid the shadow side of the skin. Now open the info - note the RGB values.
What are the correct RGB values for skin tones? I have created a skin tone gradient that mimics skin tones fairly well. In general, red is the strongest value for most skin tones; at the lightest and darkest extremes; Green is 90% of Red, and Blue is 80% of Red; for moderate skin tones (including most Caucasians); Green is 76% of Red and Blue is 52% of Red.
This map has worked fairly well for getting my skin tones close.
240 215 194
Another good option for obtaining correct values for skin tone is from other images that appear to have good color. This allows you to select a sample subject that is similar in tone to the subject in the original image. I usually go to an online catalog of stock photography, select the People category and start browsing through the CDs for an appropriate image. Here are some sample skin patches.
Now that you have appropriate values for the skin tone, you can correct to these values in the same way as correcting for white, black, or gray tones.
Create a new Levels Adjustment Layer, name it "Color Correction".
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You just need to set the values for the skin tone point to match the desired values for this skin. In this case, the point is currently at 139/126/118 (too green and too blue); based on my skin tone gradient, this should be changed to 139/107/75.
In the Levels dialog, set the channel to green, and adjust the midtone slider until the green value for the sampled point is shifted to 107. Do the same for the blue channel until the blue value is 75.
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