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Skin tones: adjusting WB & RAW calibration

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  #1  
Old 01-05-2008, 02:52 PM
switters switters is offline
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Skin tones: adjusting WB & RAW calibration

I recently bought a Canon 5D. I love it for the most part, but I'm having trouble getting pleasing skin tones in tungsten/mixed light. Obviously WB has a lot to do with that, but even after correcting for that the numbers are still off. When I say numbers, I'm referring to the CMYK guidelines (yellow should be a few points higher than magenta, cyan should be 1/4 - 1/2 the value of magenta).

I am consistently getting too much cyan, and occasionally too much yellow. I'd like to find a way to change the color calibration sliders in ACR to shift this, so I have a good starting place to work from. I have calibrated my 5D to ACR using a Gretag MacBeth ColorChecker and a script from Rags Gardner, and I've also used the process Lee Varis describes in his book to calibrate for skin. Nevertheless, I'm still not quite satisfied with the skin tones.

I know how to correct it in Photoshop, but I don't want to open every single image in PS to do this. I think it's probably possible with the right settings to do it in ACR.

Any ideas?
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  #2  
Old 01-05-2008, 06:03 PM
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mistermonday mistermonday is offline
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Re: Skin tones: adjusting WB & RAW calibration

Hello Switters,
Are you shooting in RAW or JPEG? It sounds like your combination of lighting may call for a custom WB setting. The 1st thing I would recommend is that you post a sample image or 2 for us to look at.
Regards, Murray
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Old 01-05-2008, 08:12 PM
Wolfman Wolfman is offline
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Re: Skin tones: adjusting WB & RAW calibration

Yes...... the suggestion of custom white balance is important in your case and there is something in ACR that may aid you further. It's the HSL/Grayscale section of ACR. You can fine tune many colors individually and save those setting for the particular situation you applied them to and load them later in a similar situation.
Please excuse the poor quality of image.
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File Type: jpg HSL-Grayscale.jpg (74.2 KB, 155 views)
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Old 01-05-2008, 08:55 PM
switters switters is offline
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Re: Skin tones: adjusting WB & RAW calibration

Thanks for your replies. I shoot exclusively RAW, and you're right that a custom WB would be appropriate. I have a Gretag ColorChecker, and I've determined that the correct setting for the room in question is 2400 with -2 tint (the tungsten light is very warm). Unfortunately, I can't set that manually on my 5D as 2800 is the lower limit when setting Kelvin in the camera.

Of course it would be very easy to create a preset in Lightroom with a 2400/-2 WB, which I will do now. I will also try playing with the HSL sliders a bit to see what I can come up with. Here are three examples of very different skin tones in different tungsten/mixed lighting conditions:

http://farm3.static.flickr.com/2398/...fd578515_o.jpg

http://farm3.static.flickr.com/2200/...964e0004_o.jpg

http://farm3.static.flickr.com/2293/...25e8b2b3_o.jpg
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Old 01-05-2008, 11:54 PM
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Re: Skin tones: adjusting WB & RAW calibration

Well, you are probably not going to like the answer, but here goes. What the camera computes for light balance is an assimilation of reflections, ambient light color, light levels, and the type of metering being used (spot, center, avg weighted, etc). It takes very little to shift the balance and make the resultant image look "off" especially with skin. I opened your images in ACR and moved the temperature slider to balance for the whites (eye balls and obvious background items. The pretty young women in image 1 was too yellow but it took only a very small movement to the left to normalize the cast. The 2nd image of the boy was too magenta and just needed a the temperature moved a touch to toward green. The 3rd image of the young girl was too blue and the cast was uneven (face very blue but midtones closer to neutral). This was an appropriate time to use the White balance eyedropper in Bridge. I applied it to her eyeball. This normalized the face and it may have made the background too warm but it was a tradeoff between reasonably good results in a short time.
The bottom line is that there is nothing wrong with you or your camera. Unless you have a very controllled environment (like a studio), your WB will vary form image to image. Uncorrected they still look good or at least acceptable. If you want them to look great, then you will probably need to spend the few seconds required to adjust the temperature in Bridge.
Regards, Murray
Attached Images
File Type: jpg Switters 1 MM BrTemp.jpg (192.9 KB, 118 views)
File Type: jpg Switters 2 MM BrTemp Gr.jpg (147.9 KB, 95 views)
File Type: jpg Switters 3 MM WB Eyedroppert.jpg (159.6 KB, 92 views)
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  #6  
Old 01-06-2008, 08:24 AM
switters switters is offline
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Re: Skin tones: adjusting WB & RAW calibration

I love the answer! That's exactly why I posted here. The skin tones look MUCH better. I've just purchased a WhiBal card to set a custom WB before each shoot in Tungsten light. Hopefully that will get me closer to begin with. And then it's easy to use the WB eyedropper as you suggest on the eyeballs or a white wall to double-check.

One thing I'm not totally clear on is when to use the "tint" slider. Would I use that if the image has a slight green or magenta cast?

If it's not too much trouble for you to tell me the temperature and tint numbers you used for each image, I'd like to compare them with the changes I just made. Yours still look a bit better for some reason.
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  #7  
Old 01-06-2008, 09:20 AM
switters switters is offline
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Re: Skin tones: adjusting WB & RAW calibration

Murray,

I noticed in your conversions and my updated conversions with new balance that the levels of cyan are still much higher than what is normally suggested. The images look pretty good to me, but I've learned that my eyes can sometimes deceive me - especially when I'm looking at an image or group of images for an extended length of time.

I've tried correcting for this in Photoshop by selecting a point on the red channel in curves and boosting the output (thus removing cyan). I can get the numbers to be "correct", but I often find I prefer the "greyer" version with more cyan. I guess that's not surprising because I do tend to like a less saturated look.

However, it would be good to know exactly what's happening with WB or calibration that is causing this excess of cyan. Is it possible to correct simply using WB, RAW calibration and/or the HSL sliders in ACR, or is it necessary to use curves in Photoshop?

Last edited by switters; 01-06-2008 at 09:32 AM.
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Old 01-06-2008, 11:06 AM
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Re: Skin tones: adjusting WB & RAW calibration

They eyes can play tricks on us which is why I rely heavily on the numbers. So here is the way I approached these images beginning from the simplest to the more challenging.

1. This image is clearly too yellow. I placed two color samples on neutral points (the eyeball and the wall on the viewers right). The numbers show the blue values too low; red & green are in good proportion. Simply drag the Blue - Yellow slider to the left and watch the numbers (circled in red) until the blue approaches the R/G values. That will usually do it. If you want to have a warmer or cooler look just bias it to taste. The other option is to open it in PS and add a Photo Filter adj layer after you do any other editing. I found the small shift in blue did the job. All those background neutral colors looked more natural.

2. Looking at the 2nd image, it appear to me to be slightly biased toward Magenta. Sure enough looking at the color sampler I placed on the eyeball, the Green value looked a bit low. Moving the Tint slider slightly toward Green pulled the numbers in line. When I was done it appeared a bit too yellow so I moved the temperature slider back 4 points to cool it just a tad. This is just my taste and it may not reflect the boy's true skin color but it is probably a little better because I am sure he does not have magenta skin.
BTW, after a while you get to be able to twiddle those sliders very effortlessly to make your corrections very quickly.

3. Image 3 is more challenging because the cast is not even. The light incident on the girl's face has made her skin very blue. As the light dropped off with distance (its exponential), the background was less affected and so it does not any color cast. Moreover, because the tones are not far apart it becomes difficult to affect the foreground positively without affecting the background adversely. Its a trade off and only a different lighting set up at the orig shoot would have prevent the problem. To complicate things the image is slightly underexposed.
For these types of non linear problems, the WB eyedropper in ACR is a bit out of its league on its own. In making the correction it tens to go overboard because the channels have to be moved quite far and the tool was designed for small shifts. After applying the tool to the girls eyeball, you will find the image is too bright and the cheek is getting a bit blown out. All I did here was move the Recovery slider to the right to pull down the highlights. All of the rest of the adjustment values were done automatically by the WB eyedropper tool.
4. An alternate approach to images like the 3rd one is to use another tool in PS. There is a plugin called iCorrect 1Click by a company called PictoColor. It works just like the WB tool in ACR but seems to do a better job on severe color casts. The 4th image I attached was made by clicking once on the image after I opened it in PS with no adjustments. I got basically the same result as ACR without any twiddling. But I would be interested in knowing which method you feel is closer to the real scene.
Regards, Murray
Attached Images
File Type: jpg Switters 1 ACR Settings.jpg (181.3 KB, 101 views)
File Type: jpg Switters 2 ACR Settings.jpg (171.2 KB, 71 views)
File Type: jpg Switters 3 ACR Settings.jpg (196.7 KB, 78 views)
File Type: jpg Switters 3 Picto 1Click.jpg (164.3 KB, 60 views)
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  #9  
Old 01-06-2008, 11:20 AM
switters switters is offline
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Re: Skin tones: adjusting WB & RAW calibration

Murray,

Thank you VERY much for your thorough reply. I can't tell you how helpful it is. I hope you don't mind a few more questions:

1. Is it better to place the color samplers on a neutral/white area rather than skin to make the temperature adjustments?

2. Here you're making the color judgments using RGB numbers in ACR. I am familiar with guidelines for skin tones in CMYK, but do not know what they are for RGB. How do you evaluate skin tones using RGB numbers?

3. To clarify: if the image has too much yellow or blue, I use the WB temperature slider? If the image has too much green or magenta, I use the tint slider? As simple as this seems now, I'd never heard it explained that way.

4. Do you ever use the HSL sliders in ACR, or do you rely mostly on the temperature & tint in WB to get the correct color?

5. Regarding image 3, the iCorrect version is "truer" to the actual color of the scene.

THANK YOU again! Your help is much appreciated, as this has been driving me crazy lately.

Chris

Quote:
Originally Posted by mistermonday View Post
They eyes can play tricks on us which is why I rely heavily on the numbers. So here is the way I approached these images beginning from the simplest to the more challenging.

1. This image is clearly too yellow. I placed two color samples on neutral points (the eyeball and the wall on the viewers right). The numbers show the blue values too low; red & green are in good proportion. Simply drag the Blue - Yellow slider to the left and watch the numbers (circled in red) until the blue approaches the R/G values. That will usually do it. If you want to have a warmer or cooler look just bias it to taste. The other option is to open it in Photoshop and add a Photo Filter adj layer after you do any other editing. I found the small shift in blue did the job. All those background neutral colors looked more natural.

2. Looking at the 2nd image, it appear to me to be slightly biased toward Magenta. Sure enough looking at the color sampler I placed on the eyeball, the Green value looked a bit low. Moving the Tint slider slightly toward Green pulled the numbers in line. When I was done it appeared a bit too yellow so I moved the temperature slider back 4 points to cool it just a tad. This is just my taste and it may not reflect the boy's true skin color but it is probably a little better because I am sure he does not have magenta skin.
BTW, after a while you get to be able to twiddle those sliders very effortlessly to make your corrections very quickly.

3. Image 3 is more challenging because the cast is not even. The light incident on the girl's face has made her skin very blue. As the light dropped off with distance (its exponential), the background was less affected and so it does not any color cast. Moreover, because the tones are not far apart it becomes difficult to affect the foreground positively without affecting the background adversely. Its a trade off and only a different lighting set up at the orig shoot would have prevent the problem. To complicate things the image is slightly underexposed.
For these types of non linear problems, the WB eyedropper in ACR is a bit out of its league on its own. In making the correction it tens to go overboard because the channels have to be moved quite far and the tool was designed for small shifts. After applying the tool to the girls eyeball, you will find the image is too bright and the cheek is getting a bit blown out. All I did here was move the Recovery slider to the right to pull down the highlights. All of the rest of the adjustment values were done automatically by the WB eyedropper tool.
4. An alternate approach to images like the 3rd one is to use another tool in Photoshop. There is a plugin called iCorrect 1Click by a company called PictoColor. It works just like the WB tool in ACR but seems to do a better job on severe color casts. The 4th image I attached was made by clicking once on the image after I opened it in Photoshop with no adjustments. I got basically the same result as ACR without any twiddling. But I would be interested in knowing which method you feel is closer to the real scene.
Regards, Murray
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Old 01-06-2008, 12:08 PM
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Re: Skin tones: adjusting WB & RAW calibration

Hi Chris,
1. Usually when you correct the neutral colors in an image (Black, white, Gray (gray has the greatest effect), the rest of the colors in the image tend to fall in line. Sometimes there are no neutrals in an image and you need to wing it or use the skin color.
2. I have always used RGB for skin adjustments. If you do a google search you will find free skin color charts. They have color swatches of all people's skin (Caucasian, Asian, African, etc) along with the color values. These can be used as a guide when making corrections. The other color space I use a lot of is LAB where correcting skin is a piece of cake because you mostly need to only worry about 2 value (the A and B channels).
3. Basically yes. The sliders follow a LAB color like model where you use the Yellow - Blue slider if you want to shift the color toward more Blue or more Yellow. The other slider shifts the color toward Green or Magenta. Depending on your color cast, you may need to move the combination of both sliders. The key is to watch the numbers and see how they change as you move the sliders. If the one slider can not get you into the range you want, then usually the other slider or combination of the two will move the color to where you need them to be.
4. I the temp and tint doesn't do it then I usually do a curve adj layer in PS. If the cast is not severe these sliders will almost always correct the problem for you.
5. Yes, I prefer the iCoorect myself. Not sure what algorithms they use but it seems to always do a better job on the images with severe or uneven casts. This plugin was a good investment (I think it was about $20).
Regards, Murray
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