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Sharp Flier
Sharpen your images with a gentle touch

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The image tool “Unsharp Mask” was used to sharpen the close-up of a butterfly. This tool is a powerful instrument to create images that are laser sharp - or to use excessive sharpening as a creative effect. Comparing the original with the result demonstrates the need to operate with a gentle touch.

As the name “Unsharp Mask” implies, this tool functions by first creating an intentionally softened version of the image. Combining that version with the original will yield a mostly gray mask, but with edges well defined.

The mask is then applied against the original with an algorithm that amplifies the edges, giving the image extra sharpness.

The “Unsharp Mask” tool has three controls: Effect (in Percent), Radius and Threshold. There is also an option to restrict the tool to luminance.




The “Percent” control affects brightness and contrast of the mask. This emphasizes edges in the image. The default value is 120 percent. A value of 500 percent would cause distortions due to excessive sharpness. The result would be graphical “noise” and fringed edges. For our sample picture, a value of 130 percent looks ideal.

The “Radius” controls the number of pixels involved in creating the softened version of the original. This value depends on the overall image size. An image with a large number of pixels might require a larger radius. Too large a radius can result in a halo along the edges.

“Calculate on Luminance only” is set by default and prevents undesirable color hues along the edges.

The “Threshold” defines the difference in brightness between neighboring pixels before an edge is assumed and sharpening is applied. When adding sharpness, one has to be careful about unwanted graininess or “noise”. A higher threshold value will limit this side-effect. The default threshold is set to 0, which means that all pixels of the mask are included in the sharpening.

Portraits often require a higher threshold to maintain the soft skin tones.

This example shows how well the “Unsharp Mask” tool improves the model’s hair and bikini top. The color gradients of the skin remain pleasantly soft.

The result was accomplished with these settings:

Percent: 154
Radius: 4.4
Threshold: 8

With digital photography, some sharpening is almost always warranted. There is no perfect recipe for the “Unsharp Mask” tool; each image will require careful adjustments of the tool’s settings. However, the potential for greatly improving an image more than makes up for the time invested in experimenting with this tool.