I am trying to learn more about editing skin for newborn photography in Photoshop. I understand the use of CMYK ratios for evaluating skin. However... The sample images I see online and in books show relatively low C, M and Y %s, but in my images, the CMY %s are all high (e.g. 70% for M and Y vs. 40% in the sample images). Why are my %s all higher across the board than the sample images I find? Does this mean my images are too saturated? underexposed? something else? What should I fix to get the %s lower? Thanks much.
Here is the original article linked in the small WordPress link you provided. Here is another source. I remember these techniques were from an article called "K is the key" but I can not find it anymore.
I must say: All CMYK tutorials fail to explain some fundamental concepts about RGB to CMYK conversion. They never mention that the values change dramatically using different profiles.
A CMYK value changes depending on what type of paper you want to use, the maximum absorption, therefore the color profile used.
It can also change depending on if you are using a chromatic transformation or achromatic one. This means if you want to replace neutral gray combinations of CMK with K.
It also depends on if you want to use some other type of transformation between color models, like "Perceptual" or some "colorimetry" one.
Let me explain some practical problems here.
A neutral gray, for example, it's not an equal combination of CMY inks. You could think c50m50y50 is a neutral gray... wrong.
Cyan needs to have more ink to neutralize the reddish provided by M+Y so a neutral gray needs more cyan ink. Let's say c53m48y47.
That is only one example of the problems using CMYK models to adjust colors.
You can also notice that the article says it is for prepress usage. And the article is pretty old. 2003. These techniques were used before modern color management systems.
II. A modern approach.
Use a color managed workflow, normally it consists in a calibrated monitor using specialized hardware like ColorMunky.
But you can do some basic color calibration using your graphics card.
III. Your question
A high CM+Y value could mean that your sample is too dark.
This could be because you are measuring a dark zone, you have a low key photo, or you are taking an image of a dark-skinned person. We need to see the image or a portion of it.
IV. By the numbers
If you want to try Skin color adjustments, a good approach is to first white balance your images. It is good to do this on the photoshoot.
And then probably use some RGB or LAB numbers instead of CMY ones.
Here is another post using numbers... I really need to update my answer there but can give you some tips.
I was preparing one paper on that... I'll try to work on it and update that and this answer.