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Skin Colour Correction by the Numbers?

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  #1  
Old 06-16-2008, 11:54 AM
morpheus1870 morpheus1870 is offline
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Skin Colour Correction by the Numbers?

Hey all, I have tried for the first time to correct the skin tones of this image by making reference to the actual numbers of CMYK once selected using the sampling tool. However I am unsure as to whether I have done this correctly.

The image looks better and i normally do colour corrections by eye only however as its the first time I have tried this method I was wondering if you guys can see any flaws in my workflow.

My workflow:

Step 1
Curves adjustment to set black and white points
I changed the default values to the ones below so to avoid pure black or white killing detail (is there any need for this or should the default colours be used?)
black point (r:10 g:10 b:10)
white point (r:245 g:245 b:245)

Step 2
Pick sample colour using the sampler with the 3 by 3 average option selected.

Step 3
Sampled the ladies forehead

Step 4
Read the numbers (in cmyk) and adjusted the magenta and yellow in midtones using colour balance adjustment layer so they both read 26%
(is this correct, should we aim to have these values as close to each other as possible?)

Step 5
Did a slight desaturation of the Reds using Hue/Sat layer

Overall i was happy with the improvement in the skin however not se with the green cast left in the hair, should I have sampled more areas or worked differently etc...

I am trying to learn the most accurate method to achieve the best results so your help, advice and prefered methods including your workflow are much appreciated.

I have attached a before and after below.

Thanks in advance.
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File Type: jpg before.jpg (98.1 KB, 183 views)
File Type: jpg after.jpg (98.9 KB, 214 views)
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  #2  
Old 06-16-2008, 12:29 PM
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jam1212 jam1212 is offline
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Re: Skin Colour Correction by the Numbers?

You're mostly right there.

Generally you want the Yellow to be a few points higher than magenta, and the cyan to be 1/3 to 1/4 the amount of yellow. So if magenta is 26, yellow should be somewhere around 28 or so, and cyan should be about 8 or so.

Give that a shot and see where it gets you!
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Old 06-16-2008, 12:33 PM
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Swampy Swampy is offline
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Re: Skin Colour Correction by the Numbers?

Try selecting just the skin (a loose selection with some feather) and do the HSB adjustment layer using that mask.
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Old 06-16-2008, 01:44 PM
madclark madclark is offline
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Re: Skin Colour Correction by the Numbers?

One thing to consider, if you're doing your color adjustment by eye on an uncalibrated monitor, you might as well forget it. Your results are always going to be random. Best to buy a small calibrator to really make your color corrections accurate.

The other thing I'm curious about is why you're doing the correction in CMYK mode. It's a bit unusual and I would think doing it in RGB and then converting at the end is a better work flow.

That being said, I would start out by neutralizing the picture first using a numeric curves adjustment to find your black, white and grey points.

Then generally you would reduce red a bit in Hue/Saturation and you can modify the skin color as well in the same dialogue.
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Old 06-16-2008, 02:30 PM
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snook305 snook305 is offline
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Re: Skin Colour Correction by the Numbers?

Watch the taking the red(magenta) out you have turned the hair green...
You might want to mask that off so that it does not take the skin color change as it looks fine.
Snook
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Old 06-16-2008, 04:26 PM
morpheus1870 morpheus1870 is offline
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Re: Skin Colour Correction by the Numbers?

Quote:
Originally Posted by madclark View Post
One thing to consider, if you're doing your color adjustment by eye on an uncalibrated monitor, you might as well forget it. Your results are always going to be random. Best to buy a small calibrator to really make your color corrections accurate.

The other thing I'm curious about is why you're doing the correction in CMYK mode. It's a bit unusual and I would think doing it in RGB and then converting at the end is a better work flow.

That being said, I would start out by neutralizing the picture first using a numeric curves adjustment to find your black, white and grey points.

Then generally you would reduce red a bit in Hue/Saturation and you can modify the skin color as well in the same dialogue.
Monitor has been calibrated professionally so all colours are true.

How would you suggest I neutralize the picture? what is the procedure?

Thanks
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  #7  
Old 06-16-2008, 06:39 PM
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mistermonday mistermonday is offline
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Re: Skin Colour Correction by the Numbers?

As far as I am concerned, one of the most intuitive and efficient methods of adjusting skin color is to do it in LAB color. You only need to worry about two channels (A and B) - the ratio between the values controls the whole spectrum of skin color. By looking at the color values you can tell exactly which channel needs to be moved and where.

This image is another excellent example. If you try to do a Hue / Sat adjustment, even if you tighten the range, as you lower the magenta you tend to make the hair green and you can't successfully shift the skin color without driving the lips toward yellow or green. This means adding a layer mask and masking off much of the image.

In LAB color just lay a color sampler target on a cheek which is representative of her magenta cast skin. You can see from the curve dialog box, the B channel is almost neutral (value 1). Normal skin is much more yellow. All I did was Ctrl click the sampler point to set a point on the B curve and just nudged it up. You will notice the red lips were not affected. Nor was the hair (at least not negatively).
If you find that the skin is still too green, pull down the A channel and using the same sample point, nudge the curve down between 1 and 5 points.

It is quick and effective. In LAB color you very quickly get the feel of what color skin you get based on the ratio of the A channel to the B channel.
Adjusting the L channel only affects the darkness of the skin but will give you that 3rd dimension to round out the spectrum.

Regards, Murray
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  #8  
Old 06-16-2008, 08:20 PM
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snook305 snook305 is offline
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Re: Skin Colour Correction by the Numbers?

Usually you do not want to take a reading off the cheek b/c many Ladies/girls put Blush there and that can effect your reading for sure..
In both case I find the hair on the greenish side...?
Snook
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  #9  
Old 06-17-2008, 12:26 PM
morpheus1870 morpheus1870 is offline
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Re: Skin Colour Correction by the Numbers?

Quote:
Originally Posted by mistermonday View Post
As far as I am concerned, one of the most intuitive and efficient methods of adjusting skin color is to do it in LAB color. You only need to worry about two channels (A and B) - the ratio between the values controls the whole spectrum of skin color. By looking at the color values you can tell exactly which channel needs to be moved and where.

This image is another excellent example. If you try to do a Hue / Sat adjustment, even if you tighten the range, as you lower the magenta you tend to make the hair green and you can't successfully shift the skin color without driving the lips toward yellow or green. This means adding a layer mask and masking off much of the image.

In LAB color just lay a color sampler target on a cheek which is representative of her magenta cast skin. You can see from the curve dialog box, the B channel is almost neutral (value 1). Normal skin is much more yellow. All I did was Ctrl click the sampler point to set a point on the B curve and just nudged it up. You will notice the red lips were not affected. Nor was the hair (at least not negatively).
If you find that the skin is still too green, pull down the A channel and using the same sample point, nudge the curve down between 1 and 5 points.

It is quick and effective. In LAB color you very quickly get the feel of what color skin you get based on the ratio of the A channel to the B channel.
Adjusting the L channel only affects the darkness of the skin but will give you that 3rd dimension to round out the spectrum.

Regards, Murray
A simpler method for sure, just doesn't seem to give you that fine control between the various colour values and a green tinge is still visible...guesse masking is a must either way.
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  #10  
Old 06-17-2008, 11:38 PM
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Steve Payne Steve Payne is offline
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Re: Skin Colour Correction by the Numbers?

I thought you had to work out mathematically the median value of the sample points in curves in order to adjust them properly, no?
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