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Photo Retouching "Improving" photos, post-production, correction, etc.

Skin Tone color corrections, CYMK or RGB?

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  #21  
Old 04-13-2005, 03:15 PM
McCombs707 McCombs707 is offline
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tried them all, here's what I do now....

First off, Dan Margulis is a genius, and I think his work is incredible. But, wanting to just work in RGB myself (though I work in the commercial printing field, where it's all CMYK) for my own personal photography, which will be printed on Fuji Frontier or similar equipment via sRGB, here's my formula for skin tones, at least for caucasian kids (adults are very similar)....

This is really very simple, just takes a while to 'splain'.....

After adjusting highlights and shadows via Levels, take a reading using the eyedropper with a 5x5 pixel setting of a good area of skin tone, not rosy cheek, middle of forehead works well normally. Set the eyedropper tool to display a reading in the info pallette by clicking it in the toolbar while holding down Alt (PC only, I forget which key to use on a Mac right now).

Using Curves, watch the setpoint you set in the Info Pallette and adjust the individual RGB channels to match what's below.

*** Only adjust from the UPPER RIGHT point in the Curves dialog, NOT from the midpoint or any point between lower left and upper right! Just for now, trust me!

Green - keep this constant
Red = 112.3 % of Green
Blue = 97.7% of Green

After correcting skin tone color doing the above, convert to LAB mode, and adjust contrast in Curves selecting only the Lightness channel, while viewing all channels, and adjust contrast to taste. This allows contrast adjustment without altering color range.

After all the methods I've tried, this works best, especially if you want to stay in the RGB colorspace.
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  #22  
Old 07-01-2005, 02:19 PM
jenjen jenjen is offline
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Quote:
Originally Posted by McCombs707
Using Curves, watch the setpoint you set in the Info Pallette and adjust the individual RGB channels to match what's below.


Green - keep this constant
Red = 112.3 % of Green
Blue = 97.7% of Green

After correcting skin tone color doing the above, convert to LAB mode, and adjust contrast in Curves selecting only the Lightness channel, while viewing all channels, and adjust contrast to taste. This allows contrast adjustment without altering color range.

After all the methods I've tried, this works best, especially if you want to stay in the RGB colorspace.
How exactly do you figure out the percentages? Green keep it the same right? Red 112.3% or green? How is that possible? I guess i'm calulating this all wrong. I've been trying to figure the whole skin color thing for weeks now. Thanks!

Jen
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  #23  
Old 07-01-2005, 05:09 PM
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Stroker Stroker is offline
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Quote:
convert to LAB mode, and adjust contrast in Curves selecting only the Lightness channel
Or...
Stay in RGB mode, Curves Adjustment Layer, and set to Luminosity.
Few other notes about this, but should be good enough for most.
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  #24  
Old 08-01-2005, 05:13 PM
inskip inskip is offline
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Quote:
Originally Posted by McCombs707

*** Only adjust from the UPPER RIGHT point in the Curves dialog, NOT from the midpoint or any point between lower left and upper right! Just for now, trust me!

Green - keep this constant
Red = 112.3 % of Green
Blue = 97.7% of Green
How do you determine where you ned to grab on the curve line? Can someone elaborate a little on the above formula for me? I'm not sure what
Red = 112.3% of Green means??? Keep Green constant??? Does that mean don't change it?
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  #25  
Old 08-02-2005, 10:07 AM
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Duv Duv is offline
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Quote:
Originally Posted by inskip
How do you determine where you ned to grab on the curve line? Can someone elaborate a little on the above formula for me? I'm not sure what
Red = 112.3% of Green means??? Keep Green constant??? Does that mean don't change it?
If I understand his post correctly, on the sample Original I put a sampler marker on her cheek and got readings of 219, 148, 109. Based on his percentages I should take the green value(148) and multiply it by 1.123 which gives me 166 for red. For blue I take .977 of the green value (148) which gives me 144. Therefore, I need to adjust my curves to get 166, 148, 144. He is suggesting pulling the curve from the top right corner only..not from anywhere on the curve.
I posted a Corrected Image based on the percentages and I can assure you it's not a skin tone that I find plausible. Perhaps I don't understand and need further clarification but I honestly can't see how a fixed percentage of colors can give you what you want. It certainly wouldn't work for a dark skinned person.

Cheers
Dave
Attached Images
File Type: jpg Original.jpg (36.2 KB, 115 views)
File Type: jpg Corrected Image.jpg (34.5 KB, 125 views)
File Type: png info pallet.png (7.0 KB, 81 views)
File Type: png Curve.png (8.8 KB, 73 views)
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  #26  
Old 08-02-2005, 11:07 AM
inskip inskip is offline
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Well Dave, it may not be perfect but it's definately improved quite a bit.
He said NOT to sample from the cheek, but rather the forehead which is generally not as rosy. Don't know how much difference that would make...

I'm still unclear as to how you determine where to pull on the curve-in general.
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  #27  
Old 08-02-2005, 11:09 AM
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Cameraken Cameraken is offline
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Duv

I also had a go with McCombs707 method. You have read his steps the same way I did.
His last step is to convert to LAB and adjust the lightness.
My attachment is your picture plus the last step.

I don’t look too bad to me.

Ken
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File Type: jpg Ken_Corrected Image.jpg (84.4 KB, 116 views)
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  #28  
Old 08-02-2005, 11:49 AM
fat0n3s fat0n3s is offline
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I agree with Duv on this one.

The method that is posted above, is really only changing the white point of the image. If there was a color cast, only in the highlights, then this meathod might work. If the color cast was in the midtones and shadows, this really wouldn't do any good.

There is not a magic formula for correcting skin tone. If there were, photoshop's auto color would work everytime.

Here is a good tutorial on curves. Page 3 of this tutorial gets into color correction.

http://www.gurusnetwork.com/tutorial/curves/1/

The tutorial dosen't get into great depth, but it is a good start.
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  #29  
Old 08-02-2005, 12:13 PM
Ken Fournelle Ken Fournelle is offline
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Duv,

I use your method for duplicating the RGB image, converting to CMYK, correcting and then pasting back into the original RGB image.

But don't your convert back into RGB from CMYK before your paste the duplicated image back into the original RGB image?

We discussed this in the past, and I thought that was your methodology.

k
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  #30  
Old 08-02-2005, 03:54 PM
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Duv Duv is offline
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Hate to be an old fuddy duddy here but I think my correction and Ken's are worse than the original. It's impossible for this caucasian woman to have 50% cyan with 50% magenta. Take a reading off the whites of her eyes. They've got more blue and green than red. Does that make sense? The last time I checked I had a whole pile of blood vessels in my whites which would make red the predominate color.
I've posted one here using values of about 9/42/44/0 on the marker. Cheek, forhead, nose..but it should be higlight, no shadow, makeup or natural blush if possible. This isn't suppose to be definitive or anything but using known rough values of CMYK for caucasian skin gets me one heck of a lot closer than this percentage idea. IMHO.
Ken, When you have your corrected CMYK file..flatten it, select all, copy and paste back into the original RGB file. Then change the blend mode to color.
BTW, I've tried the percentage routine on a number of images will equally poor results so maybe the original poster is not explaining something.
Inskip, if you pull from the corners of Curves you'll get more extreme changes to highlights and shadows. If you want you're change to be more transitional, pull down along the curve. For example if you want to change from 196 to 176, run your cursor along the curves line. You will see the numbers change. Locate on the curve where 196 is, click on the curve and bend it up or down to get your 176 number.

Cheers
Dave
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File Type: jpg D-Bara.jpg (97.1 KB, 83 views)
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