Unsharp Mask Sharpening Tips

When looking at photographs, the first thing your eyes notice is sharpness, followed by brightness and then warmth. But there are degrees of sharpness and depending on how images are captured some may be sharper than others.

sharpen.ssOne of the biggest advantages digital imaging has over film photography is the many ways that you can sharpen images. Most image editing programs, contain a Sharpen command that typically works by raising the contrast of adjacent or edge pixels but sometimes this technique increases sharpness at the expense of contrast. Some photographs can handle additional contrast before loosing highlight detail, while others can’t.

Instead of using the Sharpen command a better way to increase an image file’s sharpness might be using the unlikely named and wonderfully practical Unsharp Mask (Filter > Sharpen > Unsharp Mask) command in Adobe Photoshop and other image-enhancement software.

Trivia: Unsharp Masking was a traditional darkroom technique where a blurred film negative is combined with the original to highlight the photograph’s edges. In digital form, it’s a controllable method for sharpening an image than using the typical Sharpen commands.

Photoshop’s Unsharp Mask dialog box offers three sliders let you control the amount of sharpness:

  • The Amount slider controls the percentage of sharpening that will be applied to your photograph. Don’t be afraid to apply more than 100 percent to higher resolution files but lower resolution images fall apart if larger amounts are used.
  • The Radius value can vary depending on subject matter, final reproduction size, and output method. For high-res images, a Radius value between 1 and 2 is typical. A lower value sharpens only the edge pixels, whereas a higher value sharpens a wide band of pixels.
  • The Threshold slider lets you determine how different the sharpened pixels are from the surrounding area before being considered edge pixels and sharpened by the filter. On a scale of 0 to 255, using a threshold of 4 affects all pixels with tonal values that differ by 4 or more. If adjacent pixels have tonal values of 128 and 129, they’re not affected.

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Tip: Here’s a useful technique for dealing with color fringing that might occur when applying Unsharp Mask to some image files. After applying sharpening to the image , go to Photoshop’s Fade command (Edit > Fade Unsharp Mask) that appears only after a filter is applied. Don’t change the Opacity setting—leave it at 100%—but select Luminosity from the pop-up menu. Any glaring color artifacts should then be gone.

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Author: Joe Farace

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