Ah, skin. It plagues us, doesn’t it? Here’s a few random thoughts to keep in mind when you’re tackling your portraits.
You can’t edit it globally
Don’t fall into the trap of trying to manipulate white balance to make skin look good. White balance is for the overall photo. Sometimes the skin will fall into place beautifully, but other times it won’t. Don’t ruin the rest of the photo in pursuit of an easy skin fix.
Get your overall photo right first, then concentrate on tweaking the skin.
Skin can’t have a red cast
Skin is red. Therefore, it can’t have a red cast. Do you ever complain that your sky has a blue cast, or your grass has a green cast? Of course not. If your skin looks wrong, it’s because it’s either too magenta, or too yellow. Trust me.
The role of each channel in skin
Green and Blue
The Green and Blue channels combine to provide the colour. If the Green is too high, the skin appears yellow; if the Blue is too high, the skin appears pink.
If I may be permitted a broad generalisation, a regular skintone will have the Green value about 30 points higher than the Blue channel in the info palette.
The Red channel provides shape, shadow and detail in skin. Where light is striking the skin directly, the red value is high; in areas of shadow (eg under a chin) the red values are lower.
So, take somebody’s forehead as an example. You might see the Green and Blue values stay pretty much the same all the way across, from temple to temple, because the colour of the person’s skin doesn’t vary. But you’ll see the Red value go from (for example) 210 at one temple, to 250 in the middle of the forehead, back to 210 at the other temple. Because the light caught the skin most brightly at the front of the face, and fell away at the sides. Does that make sense?
There’s a common misconception that the Red channel controls the colour of skin. It does to a degree, but only incidentally. Its main role is shape.
So, you can see how any areas of skin where the Red channel is clipped can no longer have shape, shadow or detail. They’re just flat featureless areas of colour. Therein lies the importance of the Red channel.
A myth about underexposure
There seems to be a school of thought that says "if you underexpose you can’t achieve good skin". That’s nonsense, forget about it. If underexposure is necessary to avoid a sky blowout, or whatever, then so be it.
Of course, it would be terrific if every photo were perfectly exposed, but that doesn’t just doesn’t happen, right? You can make great skin from an underexposed pic, I assure you.
To you Jpeg shooters, take note – underexposed skin is easy to fix … but overexposed skin is damn near impossible. So, if you can’t hit perfect exposure, go a little under, not over.
Adjusting skin by numbers
Many people refer to the numbers in their Info Panel while correcting skin, and I am one of those people.
Numeric reference is handy when (a) you’re just learning to edit skin; (b) you’re dealing with a difficult photo; or (c) you’re editing a whole batch of photos that need to look the same.
Remember, don’t be a slave to the numbers. No matter what they say, the photo has to look right – that’s the most important thing.
The "safe zone" for skin
From my own background in the printing industry, I can tell you that we like to adhere pretty strictly to the "Yellow 5% higher than Magenta" rule. This is considered a "safe" skintone – no matter if the printing press prints the yellow ink a bit weak, or the magenta ink a bit strong, or whatever, the skin will still look acceptable. Whereas if we leave a bit too much yellow in the skin, then the pressman runs the yellow ink too heavily on the press as well, then suddenly you’ve got a hideous yellow person.
In photographic printing, we are largely immune from these kind of printing errors, as digital printing is much more controlled. But the principle is still sound.
Furthermore, you can’t always control the lighting under which people will view your photos. If you’ve erred slightly yellow in your editing, then your customer hangs your print in their yellow-lit living room, there’s a risk that it will seem overly yellow. (Of course, the human eye adapts to ambient lighting conditions to a large extent). Again, we see the benefit of "safe" skintones.
Method 1: CMYK numbers
Using CMYK values is the most common method. As already mentioned, look for the Yellow value to be a little bit higher than the Magenta value – about 3-5% is a good guide.
(There are exceptions to every rule, and I think newborn babies and alcoholic men are exceptions to this one. Don’t be afraid to let magenta go higher if it looks right.)
I’ve seen it advised for Cyan to be one third of Magenta, or something like that, but that’s absolute bunkum. If you try to uniformly match the Cyan Value to the other values, you’ll drive yourself mad.
Cyan represents the Red channel, and as I discussed above, the Red channel varies depending on how much light is on the skin. The Cyan value will operate completely independently of the other values.
The advantage of working to CMYK numbers
It works no matter what RGB space your image is in. You can edit in sRGB, Adobe RGB or ProPhotoRGB, and the resulting skintones will be the same. This is particularly handy for folk like me, working on other people’s images.
However, don’t mess with your CMYK Working Space in Photoshop’s Color Settings, or you’ll get different numbers, and that could be disastrous. Leave your Color Settings on North America General Purpose 2 unless you have very good reason to change it.
Some people mistakenly believe they need to convert to CMYK mode to edit by CMYK numbers.
Not so. Unnecessary conversions should be avoided, and conversion to a small colour space like CMYK most of all. If your photo has very vivid colours (eg flowers), those colours can die a horrible death in an instant.
It’s much better to manipulate the RGB colours, but watch the CMYK values in the Info palette. Selective Color is a handy tool, because it gives quasi-CMYK control in RGB mode.
Method 2: RGB numbers
This is less common, but RGB numbers can be used in the same way as CMYK numbers. As a general guide, look for the Green value to be 20-30 points higher than the Blue value in sRGB skintones.
People with Photoshop Elements, who don’t have CMYK figures in their Info Palette, should learn to use RGB numbers. Actually, this should be of benefit, because you’ll really learn how the three channels interact in skintones.
It’s fair to say that a lot of people who use CMYK numbers don’t fully understand the RGB colours they’re dealing with.
If you have a question about this article, please feel free to post it in Ask Damien.