Apples are red, grass is green, and the sky is blue. But what colour is skin?
Skin gives us probably the most complex range of colours in photography, ranging from the lightest to the darkest of a varying combination of colours we might identify as red, yellow, orange, pink, brown, and black. All but the very fairest skin even contains a bit of cyan.
Reproducing skin tones in your final photographs and prints can be done by eye, but you will be leaving a great deal to chance. Even when working with a carefully colour managed workflow, our eyes are easily deceived. We see skin in the midst of the colours in the background of the image, the temperature of the lighting used to take the photograph, and the clothes the subject is wearing. To reproduce beautiful, accurate skin tones, we need to learn and use a more precise method of colour management.
Moreover, skin colour varies between people, and not just by ethnic origin but also by individual. To get a grasp of just how much skin colour varies from one person to another, have a look at Angélica Dass’s project, Humanæ. Dass is not creating a technical reference, but her project highlights the technical challenge of photographing and reproducing the staggeringly various colours and shades of human skin.
This tutorial will take you through a two-step process in Adobe Photoshop that will help. First we'll explore how to balance skin colour in photographs consistently and precisely. Second, you'll learn how to make and use references from colour-balanced skin.
Colour Theory and Skin Tones
A review of some basic colour theory will help with the technical process of balancing skin tones:
A Tale of Two Colour Systems
You may recall that there are two colour systems we use in photography. The first, RGB, is the colour system we use with our cameras and computers. Colours in this system are made by combining varying amounts of red, green, and blue. The second colour system, CMYK, is used in printing. Colours in this system are made by combining varying amounts of cyan, magenta, and yellow. Because cyan, magenta, and yellow when combined produce a dark brown and not black, the CMYK system adds a pure black (the “K” in CMYK) as a fourth colour.
Skin tones are usually evaluated using the CMYK system, even when we are working on digital images on our computers. Some people suggest that it’s easier to adjust skin tones using CMYK instead of RGB, but the reason for using CMYK is likely historical. The colour references we use for skin tones were initially developed by printing press operators who work in CMYK. The references have been refined over the years, but still within the CMYK system. There is so much information about skin tones established in that colour system now that it’s easier to use it instead of trying to convert the information to RGB.
But here is something important to know: the two colour systems are not completely different or independent. Rather, they are complements to one another. In fact, understanding how the colour systems complement each other will become important as we begin to adjust skin tone.
To see how the two colour systems work together, open the Colour Balance dialogue in Photoshop (Image > Adjustments > Colour Balance) or look at the Properties in a Colour Balance adjustment layer (Layer > New Adjustment Layer > Colour Balance). Play with the colour adjustment sliders to see how the colour systems work together.
- The opposite of cyan is red. To get more cyan, you take away red, and to get more red, you take away cyan.
- The opposite of magenta is green. To get more magenta, you take away green, and to get more green, you take away magenta.
- And the opposite of yellow is blue. To get more yellow, you take away blue, and to get more blue, you take away yellow.
Colour Systems in Photoshop
It’s also important to know that Photoshop allows us to have information from both colour systems without switching between them. Even though we will be using the CMYK system to evaluate and balance skin tones, we will be working with our image in the usual RGB colour space. We will not be converting our digital files to CMYK.
Skin Tones in CMYK Values
You can find any number of suggested formulas for reproducing skin tones accurately. Image editors each have their favourites. The formulas are usually expressed as relative proportions of cyan, magenta, yellow, and black; for example:
- Find the cyan value; magenta should be double that of cyan, and yellow should be around one-fifth to one-third higher than magenta (20c 40m 50y).
But as we’ve already established, skin tones vary widely among individuals. Therefore, the best any formula can give you is a starting place. The following chart is my rough guide of CMYK values for different skin types.
Balancing Skin Tone
We are going to deal with skin tone in two parts. In this first part, we are going to balance skin tone in an image using Photoshop’s Info panel and a Curves adjustment layer. In the second part, we’ll make a skin tone reference from our image.
1. Prepare Your Image
Choose a properly exposed headshot of a person, ideally without a lot of background in the image. If possible, do a basic white-balance on your image before balancing skin tone. The technique we will be using to balance skin tone will correct overall colour balance in your image, but your work on skin tone will be easier if you are not also adjusting for a white balance skewed by basic lighting. If you are uncertain how to colour-balance your image or what it means, one of these Tuts+ tutorials will guide you: Quick Tips for a Perfect White Balance or Better White Balance with the Kelvin System.
You can do other portrait retouching before or after balancing skin tone. Sometimes, it’s easier to do retouching after skin tone has been balanced. In fact, sometimes balancing skin tone removes the need for some retouching. Other times, balancing skin tone helps to smooth out retouching that has already been done. Experiment to get a feel for what works best for you in different situations.
2. Select Your Sample
To begin balancing the skin tone, open the Info panel (Window > Info or F8) and select the Eyedropper Tool (I). In the tools options bar, set the Sample Size to sample an area of 11 by 11 pixels (“11 by 11 Average”). If your image is low-resolution, you may want to lower your Sample Size to 5 by 5 pixels.
Select a medium-light area on the skin to sample. Avoid bright highlights; the colour saturation will be too low to provide a good sample. Also avoid the cheeks; women typically have makeup there and men often have ruddy cheeks. The chin, forehead or neck are often good points to sample on a woman’s face. For men, try sampling on the forehead or below the pupils at the very top of the cheekbones. Once you’ve chosen your sample area, Shift-Click on the spot with the Eyedropper Tool to set your sample point.
In the Info panel, click on the eyedropper symbol next to the information for your sample point and from the drop-down menu, select CMYK. This will provide you with colour values in CMYK while leaving your image in the usual RGB mode.
3. Evaluate the Colour Information
Evaluate the CMYK numbers for your sample point. For example, in my photograph, the values at my sample point are:
- C - 18
- M - 48
- Y - 48
- K - 1
My CMYK chart for skin tones suggests that for average Caucasian skin, I want about 25% more yellow than magenta. In my photograph, the yellow and magenta values are the same, so I will need to add a bit of yellow.
I also want less cyan than magenta. My chart suggests starting with cyan at about 25% of the magenta. In my photograph, the cyan is about one-third of the magenta, so the cyan may need to be adjusted down.
Caucasian skin typically does not have any black, so I will want to be sure that disappears as I adjust my image. Black (as it’s read in the Info panel) is the result of cyan, magenta, and yellow combined so making adjustments to those colours will change the level of black.
4. Use Curves to Make Adjustments
To make the colour adjustments, add a Curves adjustment layer (Layer > New Adjustment Layer > Curves or select Curves from the Adjustments panel). Select the On-Image Adjustment Tool (the pointing finger) in the Curves property box.
You will be working in the individual Red, Green, and Blue channels of the Curves adjustment, so remember:
- To add yellow, take away blue; or to reduce yellow, add blue.
- To add magenta, take away green; or to reduce magenta, add green.
- To add cyan, take away red; or to reduce cyan, add red.
Working one channel at a time, click and hold on the sample point you set on the skin and move the cursor up or down to adjust the curve, adding or reducing colour as you need. The numbers in the left column in the Info panel will be your starting point. The numbers on the right are your adjusted numbers.
In my photograph, I began by working in the Blue channel to add yellow, then switched to the Red channel to remove cyan. Adjusting one channel will affect another, so you may have to make small adjustments, switching back and forth between channels until you have the colours where you want them.
5. Adjust Saturation and Tweak
Adjusting colours will affect the colour saturation of your image. So, after you’ve made your colour adjustments with Curves, adjust the saturation by adding a Hue/Saturation adjustment layer (Layer > New Adjustment Layer > Hue/Saturation or select Hue/Saturation from the Adjustments panel). Decrease the Saturation as needed.
Don’t be surprised if you find yourself going back and tweaking your Curves adjustment layer after you’ve reduced the saturation. You may also want to adjust the overall density of your image (how dark or light it is) by selecting the RGB channel in the Curves adjustment layer and nudging the overall curve (the white line in the graph) up or down.
Once you are satisfied with the skin tone in your image, save a copy before moving on to the next step.
The Reference Index: Quantifying Skin Tone
Now that you have a skin tone you’re happy with, collect a patch of skin to create a skin tone reference index.
Remove any sample points you set in the first stage by clicking on the drop down menu at the top right of the Info panel. De-select “Colour Samplers.” Flatten the image you’ve been working on (Layer > Flatten Image or select Flatten Image from the Layers panel option menu).
1. Prepare Your Samples
Choose the round Elliptical Marquee Tool (M) and select a small area of light skin (about 250 to 400 pixels in diameter). Copy the selection onto a new layer (Command/Control-J). Select a similar sized area of mid- to dark skin and copy that selection onto a new layer.
Deselect (turn off) the Background layer. You will now have two new layers, each with one patch of skin. Select the two new layers and merge them together (Command/Control-E or Merge Layers from the Layers panel option menu).
Next run a Gaussian Blur filter on the merged layer (Filter > Blur > Gaussian Blur). Choose a setting that removes any sign of grain or skin texture.
2. Create a Gradient
Select the Gradient Tool (G) and in the tools option bar, choose a Foreground to Background gradient, select Dither, and deselect Transparency.
Click on the Gradient picker in the tools option bar to bring up the custom options dialogue box. Click on the colour tag for one end of the gradient and below the tag, in the dropdown options for Colour, select User Colour. Your cursor will change to a pointer. Select one of the two skin tone samples on your layer. At the other end of the gradient, repeat the steps, choosing the other skin tone sample. Name your gradient and save it. Click OK.
Once you have your gradient options set, use the Gradient Tool to draw your gradient from left to right, completely across the layer. You will now have a layer filled with a gradient of the skin tones from your image.
3. Save your Reference File
Delete the Background layer. (Double click the layer to unlock it, then delete it.) Resize your image to something manageable (Image > Image Size). An image 1000 to 1500 pixels wide will be lots. For the Resample option in the Image Size dialogue box, choose Bicubic (smooth gradients) from the dropdown menu.
You may wish to use the Text Tool (T) and include information about the index directly in the file. For example, I added information about the skin tone and its CMYK values to my index.
Save the file as a Photoshop file (.psd) in a folder you’ve created for Skin Tone References. Name the file clearly for its reference. For example, I named my file “Male-Caucasian-Medium.”
Using Skin Tone References
Now you can refer to your skin tone reference files when colour correcting and doing advanced portrait retouching.
Open the reference file for the skin tone closest to the skin in the image you’re retouching. Use the Info panel and Eyedropper Tool as you did in the first part of this exercise to select a sample point in your skin reference file. Make note of the CMYK colour values.
Use the CMYK colour values from your reference file as a starting place to balance the skin tone as we did in stage one of this tutorial.
There are also companies and artists who make their skin tone reference files available on the Internet. Those files that include and are marked with the CMYK values may be helpful, but avoid using .jpg files that come as colour swatches only. Image files saved to the web have been separated from their source colour profile, then compressed and transformed. The CMYK values that you would read off of those colour samples are likely to be considerably off-target.
Balancing skin tone in a photograph is a challenging task but essential for producing a quality portrait. You can balance skin tone by doing a basic white-balance and fine-tuning the colours by eye, but the outcome will be easier and finer if you take the time to assess the colour values in the skin and balance them with Curves. Saving colour samples from photographs with well-balanced skin will give you a reference when colour-balancing other portraits.
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