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Sharpen faces, not the skin! The magic of the Threshold slider

(Editor’s note: This guest article is by professional retoucher Dennis Dunbar. He has been adding the Photoshop magic to images for movie posters and ad campaigns for over 28 years. He loves working on cool images with cool creatives. Learn more and see his work on his website, Facebook and Instagram.)

After working on crafting your image to be the best, just the right amount of sharpening can add the final touch that really makes the image perfect. The trick with sharpening faces is that you usually want to sharpen the features of the face but not the texture of the skin.

The image below, taken by Charles Bush, shows a close up crop of the woman’s face that has been sharpened with Photoshop’s Unsharp Masking filter. I’ve applied a heavier dose of sharpening here to make it easier to see the issue we’re talking about.

See how the eyes and hairs on the eyebrows look really nice and sharp, but we’re making it look like the poor girl has old, leathery skin?

The sharpening filter looks for any ‘edges’ or differences in values between areas of pixels and exaggerates them giving the image a sharper look. The problem is while we might like that look for some parts of the image it’s definitely not helping in other parts of the image.

I could fix this issue by masking out the parts where I don’t want the sharpening effect. In this case I’d carefully mask out the skin leaving the effect on the eyes and other parts I want to sharpen. But that can mean a lot of work.

An easier way is to use the Threshold slider in the Unsharp Mask filter. The Unsharp Mask filter gives you three sliders: Amount, Radius and Threshold. If sharpening works by exaggerating the edges in the image, the Amount slider controls how much exaggeration will be applied, while the Radius slider controls how wide that exaggeration will be. Commonly used values for these sliders range between 100-200% for the Amount and 1-2 pixels for the Radius.

But the Threshold slider is where a lot of the hidden power lies. Basically, this lets you tell Photoshop how much of a difference there needs to be between the various areas of pixels in the image. For instance, the differences between the eyebrows and the skin are larger than the differences between values in the texture of the skin. By adjusting the Threshold slider I can tell Photoshop to sharpen the difference between the eyebrows and the skin, but leave the texture of the skin alone.

The first image below I sharpened with the Unsharp Mask filter using 400% for the Amount, 2 Pixels for the Radius and 0 levels for the Threshold. The second image uses the same settings for the Amount and Radius, but 20 levels for the Threshold.

As you can see the eyes, eyebrows and even some of the hair have similar levels of sharpening applied while the skin looks a lot smoother in the one where the Threshold was set to 20 levels.

While the values used in these examples have been exaggerated to make it easier for you see what’s happening the same idea applies when using more conventional settings. Below is the same image that has been sharpened using 200% Amount, 2 Pixels Radius and 8 levels for Threshold.

Face sharpened with USM filter using 200% Amount, 2.0 Pixels Radius and 8 levels Threshold.

The bottom line is making smart use of the Threshold slider in the Unsharp Mask filter can be a powerful way to sharpen your while protecting the areas that should stay nice and smooth.

Photos copyright Charles Bush.

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