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CMYK skin tone problems/help

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  #1  
Old 01-12-2011, 03:06 PM
nikeskate875 nikeskate875 is offline
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Post CMYK skin tone problems/help

Hi everyone,

I've been having some troubles with getting the skin tones to my liking lately. I just had my monitor color calibrated and I'm trying to get better at improving on fixing skin tones. I've been using the CMYK equation (I used this article for reference), I use this method to do the actual correction, titled "color correcting skin by the numbers"& .

I find my values being so high like C-16 M-36 Y-31 (before correction). But on other tutorials I've seen the values a lot lower.

I'm not really sure what I'm doing wrong. I'm driving myself crazy on this one photo for my "100 strangers project" trying to get the skin tones correct but I just can't get it to look good. Every time I try to fix it, it just looks very off to me even though the numbers make sense. I know the numbers are just a starting point I just cannot get it to look right at all.

I'd like to be able to achieve skin tones these in the examples below where the skin looks healthy and not red and blotchy:

Example 1
Example 2
Example 3
Example 4

I've attached links the before and after screenshots of the 100 strangers photo I was talking about above. The only thing I did in the before was darken the background and fix the over all WB and on after I fixed the CMYK values in curves (didn't mask out for only skin yet)

Any help I could get would be greatly appreciated because at this rate I might drive myself nuts



Thanks
Attached Images
File Type: jpg BEOFRE CMYK SKIN FIX.jpg (96.7 KB, 107 views)
File Type: jpg AFTER CMYK SKIN FIX.jpg (94.1 KB, 109 views)
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Old 01-12-2011, 03:32 PM
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Der_W Der_W is offline
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Re: CMYK skin tone problems/help

The problem with CMYK numbers is, that they don't tell you anything about actual color.
Just in conjunction with a specific profile they're defined colors, so if your CMYK working profile (which Photoshop uses for its info palette) differs from those who created the tutorials, your results will be different.
In my opinion it's better to measure LAB color, which is not influenced by different profiles.

And you're most certainly right in that the numbers are just a starting point. Good skin tones don't necessarily go with "good" numbers and vice versa.
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Old 01-12-2011, 04:43 PM
manius manius is offline
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Re: CMYK skin tone problems/help

And how do you adjust skin with LAB?
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Old 01-12-2011, 07:04 PM
mushmush mushmush is offline
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Re: CMYK skin tone problems/help

Hello Manius,
you can use curves- they're a bit heavy handed in LAB- in my experience- use with caution.
Selective color will not work in that color space but Hue/Saturation does.

If you do use curves- watch your white point values- they can add a distinct color tone to them when the A or B channel curves are adjusted.
This can later be dealt with with a History brush or History fill- just stay in LAB.
best regards
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Old 01-13-2011, 06:03 AM
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Der_W Der_W is offline
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Re: CMYK skin tone problems/help

I did not mean going to LAB mode, but measure LAB values, that's a difference :-).

To do this just click on your color sampler in the info palette and change the readout to "LAB-Color".
Now measure a skin tone that you like, read the a and b values, go to the image that you want to apply this skin tone to and do the same.

The a value is the green/magenta axis, the b value is the blue/yellow axis.
E.g. if in your good sample the b is lower, you'll need to add blue/remove yellow on your image.
If the a is higher, you'll need to add magenta/remove green.
For this I'd just use curves, it's easy.

Btw. I did a video for this once that might clarify this topic: http://www.youtube.com/watch?v=TG9vUeT0eKk
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Old 01-14-2011, 09:21 AM
julianmarsalis julianmarsalis is offline
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Re: CMYK skin tone problems/help

Quote:
Originally Posted by Der_W View Post
I did not mean going to LAB mode, but measure LAB values, that's a difference :-).

To do this just click on your color sampler in the info palette and change the readout to "LAB-Color".
Now measure a skin tone that you like, read the a and b values, go to the image that you want to apply this skin tone to and do the same.

The a value is the green/magenta axis, the b value is the blue/yellow axis.
E.g. if in your good sample the b is lower, you'll need to add blue/remove yellow on your image.
If the a is higher, you'll need to add magenta/remove green.
For this I'd just use curves, it's easy.

Btw. I did a video for this once that might clarify this topic: http://www.youtube.com/watch?v=TG9vUeT0eKk
Nice tutorial +1

How does LAB settings work against other skin colors??? On cmyk we have basic percent based profiles for white black Asian and other skin tones how do they relate to LAB???

Last edited by julianmarsalis; 01-14-2011 at 09:27 AM.
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Old 01-14-2011, 09:45 AM
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Der_W Der_W is offline
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Re: CMYK skin tone problems/help

Thanks Julian!

For other skin colors, I don't know any ratios yet.
However it's pretty easy to find some if you're working on a calibrated monitor and have a nice skin tone available to you that you can use as a reference.

The basic principle is 0<a<b, how far both of the channels differ from 0 (the saturation) depends on the image, but probably the a would become lower the darker the skin color is (if I remember the CMYK ratios correctly that is).
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Old 01-14-2011, 01:17 PM
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Re: CMYK skin tone problems/help

The “use CMYK for skin tones” was discussed at some length here:
http://www.retouchpro.com/forums/pho...-cymk-rgb.html

Anything you can do number wise with a highly device dependent color space like CMYK (its an output space for a specific press/printer/paper combo) you can do in RGB! See post #37.
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Old 01-14-2011, 01:25 PM
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mistermonday mistermonday is offline
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Re: CMYK skin tone problems/help

Julian, I find assessing skin color in LAB to be the most intuitive, reliable, and quickest method. All of the color is defined by the A and B channels with the L channel defining the brightness. The relationship between the A and B channels immediately tell you what the skin color hue should be. Firstly normal skin has values for A and B which are both positive (>0). When the B value is lower than the A value, the skin begins to be magenta / pink looking. When B is higher than A, the skin moves into the yellow range. With both values close to 0 the skin becomes very pale. With both values in the upper 20's, the skin becomes moderately to strongly saturated. Raising or lowering the L value maintains the hue but makes the colors darker or brighter. In a very short time of viewing colors in LAB, you recognizes very quickly what skin will look like and in whcih direction you need to move to change it. You do not need to worry about complex percentages of 3 channels in RGB or CMYK. If you download a standard skin color chart and run your eyedropper around you will see what I mean.
You may also note that in Adobe Camera RAW, 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.
Regards, Murray
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Old 01-14-2011, 01:37 PM
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andrewrodney andrewrodney is offline
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Re: CMYK skin tone problems/help

Yup, you can 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 15 values difference. In Photoshop, this is a good bet. In Lightroom and ACR, you’ll have to use RGB ratio’s (no Lab readouts).

*http://www.roman16.com/en/
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