by Mike McNamee Published 01/06/2005
Skin Tone Analysis
According to some research, under normal, flat illumination, most Caucasian skin tones lie within the range shown below for mainly un-tanned parts of the body. These are lower than values we experience in "pleasing" portraiture and slightly lower than the average calculated by McCamy for the original Macbeth Chart (66%, 14, 17)
a 2 - 10
b 11 - 22
The latest Macbeth Colour Checker SG has an additional 14 patches of "skin" tones which have a and b values in the range 11-28 (a) and 17-39 (b). These are plotted on the graph along with our original test spread as used in the colour audit process for Paper Chase. Note that the SG tones are more saturated and more yellow (tanned) than any other values. For completeness we have also added the skin tones for new born infants found in a medical research paper. As you might expect
On the Professional Imagemaker we have relatively little trouble in spotting off-colour images and, with prints, we can always resort to dropping them under the spectro for confirmation. Our monitors are calibrated to an average error of less than 1 ÄE overall and, on the main workstation, the errors for Macbeth Flesh tones are 1.39 for dark flesh and 0.62 for light flesh. First of all though here is our test workflow.
1. We always shoot RAW
2. We always use a Macbeth Color Checker (24 Swatch) (and also the new SG variant)
3. We start by neutralising the image with the eyedropper to bring the colour temperature to the correct value for the scene.
4. With the image opened into Photoshop as an Adobe RGB file, we set our Info Palette for Lab and HSB readouts.
5. We scan over the image with the eyedropper set to 5x5 Pixels looking to see if most of the exposed skin lies between 16° and 24° on Hue angle. At this stage we usually ignore the saturation value. We also avoid problem areas of an image eg.
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