P: Add CMYK values in rollover, plus "skin tone" balancing

[Hard Coder]

These are sort of two different requests but they overlap.

First, for ballpark skin tone balancing, that CMYK value. RGB is useless as I think everyone knows. C/Y/M values are pretty good ballpark ways to assess whether a light-medium skin tone is realistic. For over a decade I've wondered why isn't there a CMYK option for the current RGB value displayed in the histogram area. Yes, I realize that CMYK conversion is not uniquely defined and there are color space mapping issues, but for the purpose of comparing relative values of C/Y/M, not a problem. I'm not asking for Lightroom to run in CMYK, just to do conversions one pixel or patch at a time to display a value.

Then given that, the next possibility is using a skin tone to define a white balance. So the WB dropper gets a "skin tone" checkbox (maybe with light/medium/asian/dark toggles) and you could get a ballpark WB from a skin tone dropper without having to obsess over whether it's one of those days where you will edit everything with too much magenta because there was a lot of green spill.

This SmugMug article covers the basics of using CMY(K) to balance skin tone. 

[TheDigitalDog]

Not likely this will ever happen as LR is 100% RGB in operation; it's also unnecessary.

Every flavor of CMYK is highly device-dependent, unlike RGB Working Spaces.

The idea of using CMYK for anything other than its defined output to a device is ancient thinking too. 

If you have Photoshop, simply open an image in RGB, make three duplicates, convert each to a different CMYK profile and examine the values; all different values and ratio so which is the correct one? Which should LR 'pick', which did SmugMug suggest (they didn't sadly). They are lost here.

Here's a video on correcting skin tones without having to resort to CMYK:

Low Rez (YouTube)
http://www.youtube.com/watch?v=dWaFDKrNrwc

High Rez
http://digitaldog.net/files/SkinToneVideo.mov

Keep the data in RGB and just set the info for Lab. Looking over most of the good skin tone reference files I have, including the Roman 16*, aStar and bStar are often numerically very close and never more than 10-12 values difference. As seen here:

http://digitaldog.net/files/SkinToneLAB.jpg

Work in Lab; LR supports it and it is device independent.

In Lab, the aStar and bStar values are key. Both should be positive values. Both should be within 10-12 values units of each other. If the B value is lower than A, skin starts to appear magenta or pink looking. When B is higher than A the skin appears more yellow. The closer to zero, the more pale.

You may also note that in ACR/LR, the Temperature and Tint sliders are effectively the same as the A & B channels of LAB. The Temp Axis (blue-yellow) equates to LAB B and the Tint axis (Gren- Magenta) equates to the LAB A. 

*https://www.bvdm-online.de/themen/technik-forschung/standardwerke/roman16/

[Hard Coder]

You seem to have missed the point that using a dropper or reticle while looking at some numbers is faster and simpler than opening Photoshop and running photos through different color models and looking up numbers on charts. No, using Photoshop is not an answer to "do it quickly and easily." Checking skin tones slowly and with moderate difficulty is a solved problem. I can do this in Photoshop a dozen different ways and all of them are slow, which is the problem.

Any old generic notional CMYK conversion will work just fine. The huge variety of profiles corresponds to actual output using actual media and actual dyes, which is not even remotely an issue here. "Pick a reasonable profile and go with it" works fine.

[TheDigitalDog]

Didn't miss the point, what products can you tell me that has such an eyedropper for skin tones? That works?
There is no such thing as “Generic CMYK”. 
Everything necessary to do as required can be done in Lab with TWO less numeric values and in a device independent color model in both Lightroom and ACR. And of course Photoshop. KISS.

But I will set back, see how many upvotes result and like you wait for the feature to arrive “some day”. Until then, there is a simple and very effective way to accomplish skin tone correction with only two numbers in three Adobe image processing packages.

[Hard Coder]

Well, you missed the point while pointing out that you were deliberately missing it.

An eyedropper tool for skin tone. That works. In LR. Would be awesome. And doable. And fast.

Author, Effective Perl Programming.

[TheDigitalDog]

An eyedropper tool for skin tone. That works. In LR. Would be awesome. And doable. And fast.

By @Hard Coder

I will ask again: what other image processing product has such a tool that works? 

Then I'll ask, what image processing software products have you created whereby you know such a tool is doable? 

The CMYK stuff, well, as I stated, you are welcome to ask, the likelihood is slim and why.