Smoothing the Skin Reducing Local Contrast Using Layers

In a previous post in my Lightroom series I took advantage of the Clarity tool to smooth the skin of the model. Nevertheless, the Clarity tool is not available either in Photoshop or The Gimp and many people ask how the same effect can be reproduced in these programs.

I answered this question in a previous post (Clarity Adjustment in Photoshop). The answer, however, was pretty theoretical so that in this post we will use the technique we learnt to smooth the skin in an image.

The original image, once more, is the following:

Original Image (Cropped)

The first thing we're going to do is creating a new layer duplicating the original one. Once we've done it, we use the High Pass filter to detect the transitions. The radius you need to use depends on the image (and corresponds to the amount of local contrast we're going to detect). In this image of 16 megapixels I'll use a radius of 3 pixels:

High Pass Filter - Radius: 3 pixels

We end up with a neutral grey layer where transitions are marked by lighter and darker pixels whose intensity will depend on the corresponding (underlying) pixel:

High Pass Layer

We know from our previous post that the information contained therein can be used both to raise or reduce the local contrast of our image. Since, in this case, we want to reduce it, we have to invert the layer end we end up with:

High Pass Layer - Inverted

If we now set the blending mode to this layer to Overlay the result is the following:

Resulting Image: Lowered Local Contrast

What has happened? The neutral gray pixels leave the underlying pixels unaffected. Lighter ones will screen the underlying pixels and dark ones will multiply the underlying pixels. Since pixels aren't neutral gray only at the point of transitions, we would end up with increased local contrast. However, since we've inverted the high pass layer, the local contrast is reduced.

The skin now looks smoother and you can use the high pass radius to fine tune the smoothness. However, eyes aren't sharp any more and this is something we want to avoid. Now, we have to apply this local contrast reduction only locally. How? Using a layer mask.

A layer mask is literally that: a mask, and it behaves as such. Let's imagine you take a sheet of white paper and you print your original layer over it. Now, you take another sheet of paper and you print the high pass layer over it. If you put this sheet over the other in overlay mode (assuming it would be possible), you end up with the result we just achieved. Now: you take scissors and make a couple of holes in the upper sheet just where the eyes of the model are. What would the result be? Well, the eyes from the inferior layer would be visible and wouldn't be affected by the upper layer.

Layer masks work just like that: the only difference is that you make "holes" using the black color. Layer, moreover, are more sophisticated: you can make "semi-transparent" holes using a shade of grey. Funny, isn't it?

Let's add a layer mask to our inverted high pass layer:

Layer Mask

As you can see, the layer mask is white: this means that the entire layer now contributes to the overlay effect with the lower layer. Let's now take a brush and paint over the left eye and its eyebrow. The result is:

Right Eye and Eyebrow Unmasked

As you can see, the right eye and its eyebrow have recovered all of their local contrast: pixels that we painted with black aren't affected by the upper layer any more. Let's finish painting and we end up with this result:

Final Result

You can also notice how the layer mask icon in the layers palette reflects our mask:

Resulting Mask

Conclusion

Although not available as a standalone tool, you've learnt how you can reduce the local contrast (a negative clarity, in Lightroom jargon) of a selected part of your image.

Layer mask are powerful and you can use the same technique to selectively apply any kind of effects. In this case, you could have chosen to use a blurred layer to smooth the skin, instead of going through the steps described above. Or, you could have used a bigger radius to soften the skin even more, as shown in the following picture. The only limit is your imagination.

Result with High Pass Filter, Inverted, Radius: 5 px 

With the same technique, you can enhance the eyes of the model (as described in the Lightroom tutorial), applying the same adjustments in a new layer and masking out the parts of the image you want to leave unaffected.

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Adobe Photoshop Lightroom Tutorial - Part XII - Presence Controls

Part I - Index and Introduction
Part XIII - Using Presence Controls To Enhance The Eyes

Presence Controls

Last but not least, the Basic panel offers a group of control labelled Presence and made up of:

• Clarity.
• Vibrance.
• Saturation.

For the sake of simplicity, let's start from the last one: saturation.

Saturation

To make a long story short, saturation controls the intensity of a color. The Saturation slider in Lightroom lets you uniformly modify the saturation of the colors in an image in a [-100, 100] range:

• A -100 saturation adjustment corresponds to no saturation at all and the result will be a monochrome image.
• A 100 saturation adjustment corresponds to doubling the saturation of the colors.

Beware that when you increase the saturation of an image, colors channels may be clipped and as a result color shifting may occur.

I don't use the saturation tool very often, partly because I'm not so fond of too "punchy" images, and partly because of its own non-selective nature: more often than not, I only need a more selective kind of saturation enhancement:

• I need to boost the saturation of a selected set of colors.
• I don't want skin tones to saturate and have that orange cast.

Truth be told: I almost only use the saturation slider to completely remove the saturation of an image to produce a monochrome one. Why not simply tell Lightroom to convert the image to black and white, then? Well, just because Lightroom, by default, uses a black and white color mix that's not uniform across the spectrum (as we'll see in a future post). Sometimes it's a good starting point, sometimes it's not. Only trying with a specific image can tell.

Lightroom, as we're going to see in the following seections, provides good solutions to many of the aforementioned problems, and that's the reason why I don't use the saturation adjustment so much.

Vibrance

The Vibrance adjustment is a selective and non uniform saturation adjustment with the following characteristics:

• It tries to avoid channel clipping.
• When raising the saturation, it has more effect on lesser saturated colors than on more saturated ones.
• It tries to preserve skin tones.

As a quick example, have a look at the following series of image:

Original Image

Saturation -75

Saturation +75

You can see as Saturation raises and lowers uniformly the saturation of the colors in the image.

However, this is the effect of the same adjustment using the Vibrance tool:

Vibrance -75

Vibrance +75

The Vibrance tool reduces and raises the saturation of the least saturated colors, in this case the background greens, leaving the more saturated colors, in this case the yellow petals and its orange shades toward the center, almost unmodified. In this specific case, you could also use Lightroom to selectively raise the saturation of the green channel (as we'll see in a future post).

However, the Vibrance tools is a handy tool that can help you apply saturation adjustment in a really quick way, especially in portrait photography when things can get really tricky when trying to preserve the skin tones of our models. Had we applied such a saturation adjustment in a portrait, orange shades would probably had popped up in our subject's skin pretty much as they popped up in the petals of this flower. In those cases, only Photoshop would be your friend: you'd use layers and layer masks to preserve the tones in selected image regions. Fortunately, Lightroom gets in the way and provides this quick solution to such a common problem.

Clarity (And Local Contrast)

The Clarity adjustment lets you add depth to an image by modifying local contrast. But what's local contrast, first of all? Here's a really quick introduction about this problem.

The physiology of the human eye is such that, in certain circumstances, a photo cannot be a faithful representation of what we perceive. This is especially true when dynamic range is taken into account. You have surely noticed how a well your eyes can see a scene with a high dynamic range (such as a landscape with both strong lights and deep shadows) and how bad the same scene look when you shoot it, no matter the effort you put into it. When we move our eyes around, they'll quickly adapt to the light conditions of the part of the scene we're focusing on, although you may have the impression of perceiving the entire scene as if no adaptation has occurred. On the other hand, when you take a shot you have to choose an exposure, and if the dynamic range of the scene you're taking is too high, you will simply miss the shot: either you burn the highlight or you lose details in the shadows. If you've heard about HDR (High Dynamic Range) imaging, you'll probably realize what the central idea of that technique is: you take multiple shots of the same imaging bracketing the exposure and blend them together in a single image, preserving the intensities you need across the dynamic range of the picture. This way, you artificially build a visual representation of what our eyes perceive when they move, and compensate, across regions of the image with big luminance differences.

You may think of local contrast as a technique to achieve the opposite goal: you selectively raise the contrast of light-shadow transitions to give more dynamic range to your image. However, instead of raising the overall contrast of the image (where both white and black points are moved and clippings may occur), the adjustment in only performed in smaller regions of the picture, leaving the overall black-white difference unmodified.

Lightroom lets you adjust the local contrast by both positive and negative values, in the [-100, 100] range.  Let's see some examples of how Clarity works.

Original

In this picture, the majority of pixels find themselves on the opposite sides of the range: the background is nearly black and the flower is white. Neither white nor blacks are clipped. Since the maximum luminance difference in the flower's pixels is less than 1 f-stop away, you may want to apply some adjustment to give the flower some more depth. Raising the overall contrast, as we've seen in a previous part, will only make things worse:

Contrast +100

Raising the overall contrast is going to raise the differences between black and white, but doing so means compressing whites even further, and the result will be a flower even flatter than before. You may be tempted to apply the opposite adjustment and bring overall contrast down:

Contrast -50

In fact, reducing the overall contrast expands the histogram in the recovery and in the rightest part of the exposure zone pushing them towards the center of the histogram. The flower will indeed gain depth. Unfortunately, the overall contrast reduction is going to expand the blacks and the shadows as well, pushing them towards the center of the histogram. The final result is not probably what we were looking for since the image is now flatter and duller.

Once again, there's no need to leave Lightroom and open Photoshop. The Clarity adjustment is just what we were looking for:

Clarity +50

Increasing the local contrast has raised the depth of both the flower and the leaves, leaving the overall contrast unmodified. The white and the black points do not move and we introduce no clipping at all.

Clarity adjustments are often subtle, and I suggest you zoom out when you apply it. Nevertheless, it's a very handy adjustment which many pictures can benefit from. Look at the following example (to appreciate the difference you may need to open the liked image):

Original Image

Clarity +60

Original Image

Clarity +75

Negative Clarity

The Clarity tool lets you apply negative clarity adjustment. Why would you want to reduce the local contrast of an image? Reducing local contrast has a softening effect that may be result pleasing in some kind of photos. Some portraits and some nature images, for instance, may benefit from a slight reduction of clarity, if you want to achieve a "dreamy" or "soft" mood without spending much time on applying more complex effects such as the Orton effect. In the following example you can see how a negative clarity affects the image of the two purple flowers that we've previously seen:

Clarity -50

Local Contrast in Photoshop

The Lightroom Clarity tool is a very handy tool: you can brush a negative clarity adjustment on the skin of your model, for example, as a quick and effective way to smooth his skin. I often hear people ask how can local contrast be adjusted in Photoshop. It's not as straightforward as in Lightroom but I described an  easy way to achieve the same effect in another post.

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