Clarity Adjustment (Local Contrast) in Adobe Photoshop

In a post of my Lightroom tutorial series, we've seen how the Clarity tool lets you apply both positive and negative local contrast adjustments. The Clarity tool comes from Adobe Camera RAW, used by Lightroom under the hood, and it provides a really quick and easy way to perform a task that, otherwise, would require much more time to achieve.

Adobe Photoshop, for example, does not provide such a simple way to modify a picture local contrast and by its own nature, this kind of adjustment cannot be achieved with tools that modify the overall image, no matter how complex they are: you are not going to raise only the local contrast using the Contrast, the Levels or the Curves adjustment.

Even if you're a Lightroom user, there are times when you're going to use Photoshop (or similar programs) in your workflow: I deem necessary to know how you can achieve the same result when you cannot rely either on Camera RAW or Lightroom. The good news is that you can achieve the result both in Photoshop and in Photoshop Elements, the stripped down version of Photoshop aimed at beginners and amateurs.

The Unsharp Mask

The Unsharp mask is a tool that's best known to Photoshop users to sharpen an image. It's funny how names can be so misleading at times, isn't it? If you're interested about the history of the technique this name comes from, you can have a look at the Wikipedia article about it.

However, as far as we're concerned, the important thing is the following: the unsharp mask can be used to raise the local contrast of an image in a very simple way.

You can see the Unsharp mask window in Photoshop Express in the following picture:

Photoshop Elements - Unshard Mask Window

Unsharp mask adjustments are applied according on three parameters:

• Amount.
• Radius.
• Threshold.

Usually, when you use the Unsharp mask tool to sharpen an image you select a relatively small radius and a large amount. On the other hand, if you use a relatively large radius and a small amount, the effect will be a local contrast enhancement. If you read the Wikipedia article about this technique, the radius is used to tell how much the image should be blurred during the process of detecting transitions.

In the following example, you can see the effect on the same image we used as an example of the Clarity adjustment in the aforementioned post:

Original Image

Unsharp Mask - Amount 20%, Radius 50, Threshold 0

What About Negative Clarity (a.k.a., Reducing Local Contrast)?

The Unsharp mask is an easy way to enhance the local contrast of an image: so far so good. But if you've used the Lightroom Clarity tool, you're probably missing negative clarity adjustments as well! There's no way to reduce the local contrast using the technique seen so far and you must rely on other tools.

To understand how you can achieve negative clarity, we will first look at how positive clarity can be achieved manually (reproducing the steps that are performed by the Unsharp mask tool).

The first steps is detecting transitions. In film photography, the process was pretty complex. Photoshop makes it easy: that's what the High pass filter is meant for. If we use a radius of 1.5 pixels, this is the result:

High Pass Filter - Radius 1.5 pixels

The result is:

• Neutral grey pixels where no transitions were detected.
• Colored pixels where transitions were detected.

This new layer will be superimposed to the original using the Overlay blending mode. The neutral grey pixels won't affect the underlaying pixels while pixels marking transactions will enhance the local contrast. This happens because the Overlay blending mode multiplies (darkens) dark areas and screens (lightens) light ones. The final result is the following:

High Pass Filtered Layer Overlaid on the Original Image

There's no doubt that using the Unsharp mask tool is much quicker when we need to enhance local contrast. What about negative clarity, then? Simply invert the layer generated by the high pass filter:

High Pass Filtered Layer Inverted and Overlaid on the Original Image

Pretty much the same effect you'd get in Lightroom using negative clarity, only a bit more difficult.

Adobe Photoshop Lightroom Tutorial - Part XII - Presence Controls

Part I - Introduction
Part II - Lightroom Workflow
Part III - Organizing the Library
Part IV - Keywording and Metadata
Part V - Using Filters
Part VI - Importing Your Images
Part VII - Basic Editing Tools
Part VIII - Developing Your Images, The Basics
Part IX - Reading and Interpreting the Histogram - Basic Adjustments
Part X - White Balance
Part XI - The Tonal Scale
Part XII - Presence Controls
Part XIII - Coming Soon!

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

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