CMYK and skin-tone editing in C1 5 Pro

[mweiner]

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Over in the M9 forum thread "M9 Color (from a newbie)" , there was some discussion of editing skin tones in C1 5 Pro and also a reference to:

help - How to get pleasing skin tones on prints which gives advice on how to attain pleasing skin tones by CMYK editing. This has led me to several questions involving C1 where I'd appreciate some help.

 

1.) How does one measure and edit the CMYK values in C1. ( I have figured out how to do that in PhotoShop but would rather do it in C1.) So far the best I can do to get C1 to show the CMYK values is to go to VIEW > Proof >Profile and then for where the cursor points, they show up where the RGB values were. However, then I'm stuck about how to edit these. All the sliders I can find (eg in the Color Balance, Color Editing, Advanced, and Skin Tone tools) are in RGB. The 'curves' input/output channels are also all RGB.

 

2.) As a related question, the CMYK proof (monitor) profile I choose seems to change the color representation of the image on my screen from the calibrated profile (from colormunki) that I assume gives the correct representation -- so even if I were able to be editing skin tones using that proof profile, I wouldn't be seeing the colors properly.

 

3.) As another related issue, I have watched the C1 videos about the color-editing>skin-tone tool and also the 'skin tone' tool. However, I don't seem to be making much progress learning to use these effectively for skin tones. Any practical advice would be appreciated.

 

I like using C1 (and hate using PS), and am hoping for some advice about how I can use C1 to edit skin tones -- esp by adjusting CMYK proportions.

 

Thanks for any help.

 

Michael

[erl]

Sorry to 'answer' your question with a question, but why do you want to use CMYK instead of of RGB? Your monitor and printer work in RGB. Maybe you are sending the files out to a pre-press agency who specify CMYK.

 

I don't pretend to be any sort of expert but others here will doubtless tune in with more helpful comments. I will stay tuned as well.

[mweiner]

Erl, thats a good question. The best references I've found on the web discussing how to adjust skin tone all assume working in CMYK. These include:

 

* The thread you started in the M9 forum ("M9 and skin tones"). In that thread the most precise discussion of your skin tones (eg by Jamie Roberts and adan) is in terms of CMYK. sclamb gives a link to this reference -- all in terms of CMYK -- (also suggested by Jamie) and which is very commonly found when looking for skin tone "how to":

 

help - How to get pleasing skin tones on prints

 

* There is a fair PS skin tone how to on peachpit.com which discusses combining RGB and CMYK. The author discourages RGB<>CYMK mode changes and gives some information on using RGB, but still ends up doing the the crucial adjustments in CMYK:

 

Peachpit: Working with Color in Photoshop > The Numbers Don't Lie

 

The best discussion I've found of the pros and cons of using CMYK, RGB, and a combination is here:

 

Skin Tone color corrections, CYMK or RGB? - RetouchPRO

 

That discussion suggests why there may be no CMYK in C1 -- if our experts tell us that is indeed the case. A comment by Jamie Roberts in the recent M9 thread "M9 color (from a newbie)" seems to imply that he goes from C1 > TIFF >PS for these kinds of adjustments, but I would love to know more clearly his workflow for handling skin-tones -- especially in view of the pitfalls discussed in the retouchpro.com link above.

 

Thanks for your interest and keeping this thread alive in hopes we may get more advice.

 

Michael

[pop]

Your monitor and printer work in RGB. Maybe you are sending the files out to a pre-press agency who specify CMYK.

 

I am not an expert, either, but I can see why the question might be more important than it seems at first.

 

Most printers I am familiar with use the CMY or CMYK color spaces. That might be related to the fact that the monitor works with additive colors while the printer works with subtractive ones. In the RGB space, larger number make brighter dots. In the CMYK space, larger number make darker spots.

 

There is no perfect translation of an image from RGB space to CMY(K) space. Where the resolution is best in one color space, it will be worst in the other one.

 

A properly calibrated color management system will certainly help in this conversion, However, I fancy that there might be situations where the last fine tuning of the color rendition has to be done within the color space which is used on the output device.

 

Unfortunately, this is where my knowledge finds its limit.

[mweiner]

Well, as I think I understand it, modern print drivers, such as those for the epson 3800, are designed to expect RBG input and then they do the worrying about converting to printable information. Therefore, ordinarily most of us wouldn't have to worry about CMYK, except that our color experts (and many others) give us their best skin-tone advice in CMYK -- probably for the historical reasons you describe.

 

Maybe the question we should be asking of our color experts is:

"Can you give us in RBC terms advice about values and methods of adjustment that is as specific and replicable as what you have given us in CMYK."

By the 'can you', I am really asking ' _can_ you' (as well as 'would you').

 

Michael

[adan]

As someone who worked in the print industry for 23 years (newspapers), the underlying truth is that there is not a perfect correspondence between CMYK and RGB. Mostly due to the fact that there is a a colorless color (black) in CMYK images.

 

For those who have PhotoShop, this is easy to see for yourself. Go into the Edit menu > Color Settings and select Working Spaces > CMYK > Custom CMYK....

 

This brings up a whole lot of options and graphs to tell Photoshop how to "separate" or convert an RGB image into CMYK for a printing press. What you will see is that these curves are very non-linear, mostly because of techniques called "Undercolor removal" or "Gray component removal." And also because of dot gain settings - the amount the ink spreads in the paper fibers.

 

Those techniques are to save ink - it is a whole lot cheaper (and leaves less ink piled up on the paper to rub off on your fingers) if, say, a dark red is printed as mostly black ink, with just enough magenta and yellow to tint it red (and no cyan ink at all). The curves can be varied to determine how strongly the conversion process reduces the amount of color inks.

 

(BTW these settings, as already mentioned, play no role in printing to an inkjet printer. The printer drivers and the profiles used for printing do their own conversion to CMYK on the fly, without reference to the Color Settings)

 

The CMYK values the Photoshop eyedropper/Info dialogue will give you ARE dependent on what color settings you are using.

 

In addition, inks themselves are not linear. One would expect the purest red (255R/0G/0B) to be printed as 100M/100Y/0C/0K - but in fact that almost always comes out something like 95M/92Y/0C/0K.

____________

 

But - to finally get back to the original question: The basic rule of thumb in CMYK is that "yellow should be 10-15% higher than magenta" - e.g. skin might read 25M/30Y.

 

In RGB, you just take the complementary colors and reverse the relationship - i.e. "Blue (complement of yellow) should be 10-15% LOWER than Green (complement of magenta)".

 

If one takes the Macbeth Colorchecker "Light Skin" color patch as an example - it may not be everyone's ideal for skin tone, but it is a very good match for my skin, as it happens - the RGB values come out something like:

 

Red - Green - Blue

205.....163.....144 or

190.....147.....127

 

red is high, green and blue are lower (or you'd get gray), and blue is lower than green (to increase the yellow) by - in this case - 13%-16%.

 

Of course, that is for caucasian skin (presumably that of a Super-model) - ethnicity, age and a host of other factors will affect the "correct" RGB values for any given person's skin.

[Jamie Roberts]

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{snipped}

 

That discussion suggests why there may be no CMYK in C1 -- if our experts tell us that is indeed the case. A comment by Jamie Roberts in the recent M9 thread "M9 color (from a newbie)" seems to imply that he goes from C1 > TIFF >PS for these kinds of adjustments, but I would love to know more clearly his workflow for handling skin-tones -- especially in view of the pitfalls discussed in the retouchpro.com link above.

{snipped}

 

Of course there's a CMYK in C1 Mine is set to CMYK for precisely the reasons you mention. I do 99% of all skin tone adjustments in CMYK from capture through to PS.

 

In C1, just go to View...Proof Profile and select the CMYK you want to work in. I use the SWOP v2 (US Web Coated) profile because it carries over nicely into PS.

 

Does that answer your question? I can get skin pretty much where I want it in C1 then totally nail it in PS, and it doesn't matter what RGB space I'm going to

 

I know, by the way, this is controversial. But like many things controversial, it works.

 

Are there RGB equivalents? Yes... sort of, as Andy suggests above.... one "set" for every RGB space

 

Note that I'm not advocating you OUTPUT to CMYK as a workflow (unless you know why you're doing that--there are some reasons); only that you measure there (in the proof space) as a consistent way of looking at cyan, magenta, yellow and black content for skin.\

 

Now, if only C1 would let me look at RGB and CMYK profiles at the same time, like I can in PS, then I'd be a happy guy

[mweiner]

Yes, Jamie, that was exactly the information I was looking for.

 

Lots of thanks,

Michael

[mweiner]

adan, your information was interesting and I'll try it, but not as specific to C1 -- which as I recall you are more of a LR/ACR user. Interestingly, it was your useful reference to the smugmug skin-tone article in the "M9 color (by a newbie)" thread that immired me in CMYK in the first place. In general, I have learned a lot from you, Jamie Roberts, erl, and others on this and the M9 forums.

 

Michael

 

Edit: Duh, I just realized that you were in fact giving a detailed answer to my question "_Can_ they" explain the CYMK values in RGB. I'll need to give some more time to pondering your post.