Super Skin Mask: The Magic of the Red Channel

Posted: June 23rd, 2009 | Author: admin | Filed under: Uncategorized | Tags: masking, retouching, skin, skin color, skintones | 7 Comments »

Last week, Jodi Friedman reviewed the basics of masking. I find that, more often than not, some masking is necessary over the course of the skin correction process. It’s critical that you understand the fundamentals of masking, but I’m also all for any technique that can make masking (and post processing in general) more efficient / less painstaking. Today I want to share with you a quick automatic masking technique that I use with virtually all of my skin corrections.

Let’s start with a basic skin correction. This week’s image comes from Vermont-based photographer Lisa Harrison, and she was kind enough provide this beautiful SOOC image:

I took a sample from the middle of the girl’s forehead, and it yielded the following CMYK values:

C: 22%

M: 19%

Y: 15%

K: 0%

The first thing that you should notice is that the cyan is way too high. The magenta is pretty high, too (or the yellow is too low), but we’ll get to that in a minute. Let’s focus on the cyan. The most straightforward way to correct an excess of cyan is to pull up the red curve:

… which resulted in this:

Now the cyan (4%) to yellow (12%) ratio looks fine, but the magenta is still much too high, so let’s bring that down by pulling up the green curve:

And the result:

This looks pretty good, but there have been a few unintended consequences of the color correction that you may or may not like

1) The eyes are less vibrant (because we warmed up the blues)

2) The grass is more yellow

3) The shirt has a faint red tint

4) The hair has taken on a reddish hue

I don’t think any of this is particularly objectionable, but oftentimes you want to correct the skin without dramatically affecting the rest of the image. So, what to do? Well, you could do regular masking like we learned about last week ….  I’m going to mask off the grass, shirt, hair, and eyes:

Okay, that just looks TERRIBLE (I was horribly sloppy on purpose, because I’m trying to make a point)….

With a little more time, care, and brushes of varying opacity, you could actually make that look pretty good.  The grass color looks fine, and the irises look fine; the whites of her eyes, on the other hand, look ridiculously blue, the shirt is also unrealistically cool compared to the skin, and the transition along the hairline is pretty clearly atrocious.  My point, however, is that sometimes it’s really difficult – particularly along the hairline and where the hair touches the clothes or background – to get a clean mask. There’s an easier way. Stay with me …

I’m deleting the horrible mask I just did. Now I have an empty mask again. Here comes the magic …

Select the mask.  Go to Image>Apply Image. Use the following settings:

Layer: Merged

Channel: Red

Blending: Normal or Multiply (it doesn’t matter)

Click OK.

Revel in the awesomeness of your mask. Here’s the result:

Here’s what the mask looks like:

This mask works just like any other mask: white reveals, black conceals.  Therefore, your curves adjustments are being applied wherever you are seeing white or very light gray above (THE SKIN, the shirt, the highlights of the hair); the curves adjustments are not being applied to the grass or the eyes and are applied minimally to the hair. Don’t want the adjustments applied to the shirt (for example)? Just paint black over it!

Sometimes a little more tweaking is still required. The mask can change the skin values by 1-2 points (rarely more), so sometimes you need to adjust your curves a little more after applying the mask, or you may want to just reduce the opacity of the mask a little bit.  Sometimes I also increase the contrast to the mask itself to make the light grays whiter and dark gray darker (with the mask selected, go to Image>Adjustments>Curves/Levels/etc).  As I alluded to above (when I suggested painting the shirt black on the mask), I also may use a brush to fine tune the mask by hand.  Overall, I use this Apply Image method on almost every skin correction that I do, and it accomplishes at least 90% of the masking for me automatically.

In this case, I might go in with a soft black brush (about 30% opacity) and bring some of the grass back in (I like the warmer color that came with the correction). Right now, however, I just want you to see the difference that the mask alone creates. Here’s the difference between the basic correction and the corrected version + Red Channel mask:

And here’s the original compared to the corrected/masked version:

One more example of the mask in action:

Original:

Corrected:

Red Channel Mask Applied:

Go try it out! That’s it for skin this week!

A PDF version of this tutorial is available here.

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