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Clarifying the Clarity Slider

An entry in my dictionary defines "clarity" as "clearness or lucidity of understanding." In spite of this, it's not at all clear what the slider labeled "Clarity" in Adobe Lightroom and Camera Raw actually does. Let's see if we can clarify things a bit.

First, you can only find the "Clarity" slider in both Lightroom and Camera Raw. Vibrance, the other newfangled slider originally only in Lightroom and ACR got added to Photoshop as of CS4, but so far, Adobe hasn't seen fit to give us Clarity adjustment layers in Photoshop. There are workarounds though as I'll discuss later on.

Next, some readers may be satisfied just by opening an image in either of the two programs that do have a Clarity adjustment, pushing the slider back and forth to see what affect it has and not worry about what's actually going on when they use it. Slide it all the way to the left and the image gets notably softer. All the way to the right and it gets sharper. So in this sense, Clarity appears to be another form of sharpening.

If you look it up in the Adobe documentation, Clarity is listed as adding "depth to an image by increasing local contrast, with greatest effect on the midtones. This setting is like a large-radius unsharp mask." I've described the use of unsharp mask to increase local contrast before. Normally, the radius slider of the Unsharp Mask dialog limits its effect to what it perceives as edges in an image. It accentuates contrast along those edges by darkening one side and lightening the other. But if you increase the radius sufficiently, the effect broadens accordingly. Rather than increasing contrast just along edges, its effect takes on the appearance of increasing local contrast more generally. A low amount and high radius in Unsharp Mask works to give an image more pop, not by adding any additional contrast overall, but by rearranging the contrast the image already has to create a more visually compelling result.

But unlike the method of adding localized contrast with Unsharp Mask, if you look closely at what Clarity does, it doesn't affect everything in an image equally. Just as Vibrance works mainly on portions of an image that aren't yet overly saturated, Clarity adds localized contrast mainly to portions of an image that don't already have lots of contrast. Existing high contrast edges naturally require that one side of that edge be bright and the other dark. If both are relatively the same tone, the edge simply wouldn't look very contrasty. Most of what Clarity does is intentionally limited to the midtones too since the human eye senses contrast mainly in the midtones. Broad areas that are exceptionally dark or bright just never look all that contrasty to us. This is the theory behind the use of S-curves for improving the perception of image contrast. Internally, the Clarity adjustment creates a mask of areas within an image that would benefit most from having greater local contrast and works only on those. Clearly (if you pardon the overuse of that word), Adobe has put some serious thought into making the Clarity slider useful.

Some time back, Mac Holbert of Nash Editions devised a similar technique for improving midtone local contrast. You can try his method out for yourself by duplicating your image layer (or using Edit >> Copy Merged followed by Edit >> Paste if you already have a layered document) and setting the blending mode of the resulting layer to Overlay. Then change the opacity of this new layer to around twenty percent. You won't see much of a change yet, but bear with me. Go to Filter >> Other >> High Pass. The preview in the filter dialog will look like a haloed black and white version of your image. Adjust the slider to a radius of around fifty pixels. Look for the point where the preview image first starts to show any color. Click OK. Finally, right click on this layer in the Layers palette and go to the Blending Options. In the section at the bottom for "Blend If" move the "This Layer" slider black point slider to a 50/70 split. You'll need to hold down the Alt (Option key on Mac OS) to get the black triangle to separate. Then do the same thing with the white point slider to create a 185/205 split. Click on "OK." Raise or lower the opacity of your Overlay layer to fine tune the adjustment.

You can find descriptions of similar techniques with slightly different steps if you Google around a bit. One method uses a similar blending option split to constrain the effects of the large-radius Unsharp Mask technique mentioned above. The Clarity slider obviously is easier than any of these methods and quite likely better since its algorithm is adaptive and automatically adjusts its results to make use of the different qualities of each portion of the image it is being used on. Hopefully Adobe will see fit to add Clarity to the next release of Photoshop.

You might be tempted to use Clarity as a substitute for sharpening in some cases but since it operates over a relatively large radius it really won't sharpen nearly as well as Smart Sharpening or even Unsharp Mask used with an appropriately smaller radius and higher amount. But Clarity is great for adding a touch of, well... "clarity" to an image.

Clarity adjusted to the minimum
Clarity adjusted to the minimum
Clarity set to the midpoint (default setting)
Clarity set to the midpoint (default setting)
Clarity adjusted to the maximum
Clarity adjusted to the maximum

Date posted: March 13, 2011


Copyright © 2011 Bob Johnson, Earthbound Light - all rights reserved.
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Related articles:
Stealing Contrast with Photoshop Curves
Improving Local Contrast with Unsharp Mask

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