Most people don’t like seeing themselves having too red, or especially magenta, skin tones.
However, this easily happens, and the typical technical causes are either improper white balance, some sensor hypersensitivity at IR wavelengths, or possibly post processing trying to increase the saturation (”Velvia look”).
When is it not right?
But when is the red or magenta too much? Turns out there are easy rules in the CMYK colour space.
For most caucasian people, there should be more yellow than magenta, and considerable less cyan. You need to read Dan’s books (e.g. Professional Photoshop, 5th Edition) to get all the details, but there is a quick summary of these rules and how to deal with them over at smugmug.
Those key rules are that
- Yellow should be larger than magenta,
- with cyan typically 30% to 50% of the magenta value,
- and magenta never more than 50.
For different types of skin, the key take-aways are (as copied verbatim from the link above, which again is taken from Dan’s excellent book):
- A fair-skinned pinkish baby could be as light as 15% magenta, 16% yellow.
- Most caucasians fall in the range of 5-20% more yellow than magenta.
- A fair-skinned caucasian adult could be as low as 20% magenta, 25% yellow.
- A bronzed caucasian could be as high as 45% magenta, 62% yellow.
- Asians and hispanics have typically 10-20% higher yellow than magenta.
- If magenta is getting towards 50%, beware of the well-done look.
- On pleasing photos, cyan usually falls between 30% to 50% of the magenta value.
- Less than 30% of magenta makes sunburn; more than 50% of magenta makes makes them ghostly blue.
Correcting skin tones
If you have incorrect skintones, how should you then deal with them?
Seldomly is selective adjustments needed; you should be able to get away with global corrections in most cases.
There are multiple ways of doing this, but the simple and the better ways are as follows:
Simple correction (working in RGB mode)
- In Levels, set the gamma (middle adjustment that by default is 1.0) of the blue channel to 0.90 or even down to 0.85 in extreme cases.
- In Hue/Saturation, desaturate the red channel with -7.
Better correction (convert to CMYK mode first)
- Go to the curves adjust dialog
- Ctrl-Shift-click on a representative skin tone to set a point in each channels
- Move the magenta point down (never horizontally!) so that it is less than where you intend the yellow point to be.
- Move the yellow point up (also vertically!) so that it is a bit higher than the yellow.
- Adjust the cyan point (vertically!) to be around 30% to 50% of the magenta value.
You may need to convert back to RGB afterwards. How do you pick the target magenta/yellow values? Pick something that is not too far from the original values, and use your eye to judge the overall picture and the skintones.