I’m trying to get a CYMK output with values for a specific point in an image in order to review skin tones. The navigator only shows RGB, HSV, and Lab*. Is there another information panel for this?
Underlying theory is that a good skin tone is C=value, M=C2, Y=M1.25.
Thanks!
No, and the CMYK color model is not supported, however you could convert your desired skin tone value from CMYK to RGB/HSV/Lab, then soft-proof in RT using a CMYK printer profile and match the RGB/HSV/Lab values.
http://rawpedia.rawtherapee.com/Preferences#Color_Management_Tab
http://rawpedia.rawtherapee.com/The_Image_Editor_Tab#Monitor_Profile_and_Soft-Proofing
Fantastic. Thank you! I was having trouble trying to figure out the conversion.
“CMYK” like “RGB” is a device dependent colorspace. So there can be no general rules such as you show. Typical ranges of skin tones may be specified in terms of device independent colorspace value with some meaning (i.e. L*a*b* or L*C*h* values, i.e. see this etc.), and you can convert to/from such colors using an ICC color profile for the particular CMYK device you are dealing with.
Unfortunately, there is a lot of literature out there that uses device dependent colour spaces…
I think Dan Margulis popularised the CMYK-based colour-correction. SmugMug references him when they explain the correct skin tones formulae.
The thing about skin colour is that it is so diverse that it fills more of the spectrum than we realize. Even our own skin varies with time, age, health, weather, light source, etc.
This subject reminds me of https://www.angelicadass.com/humanae-project/.
That’s old fashioned press operator stuff. Many of them are/were super expert at judging how to tweak the CMYK on their presses. It’s of less use when a CMYK device could be an offset press, a digital press, a color copier, an inkjet etc., where the color of the inks and the tone reproduction curves are quite varied. It’s even less use to mere mortals who don’t have the years of CMYK experience behind them. (And amusingly, ask many of the “CMYK under the fingernails” folk what RGB tweaks to make, and they have even less intuition about it than you or I 
The fun part is that Dan started popularizing LAB just a few years after the 2002 book and never stopped since.
Looking at the ratio of C/M/Y would work. I suppose looking at the ratio of R/G/B will work as well.
L* a* and b* values are more difficult I suppose as it is harder to get a feel for the a* and b* value perhaps. L* might drop out, so that would be easier.
Here is a file that dates back to 2011, which takes the values of skin values Lab (actually Lch) which is used to weight the action when the user wants to change the chromaticity
skin.txt (4.5 KB)