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An Unsharp Mask is essentially a Blur in reverse. A Gaussian Blur
is applied to a copy of the original image to produce an image with
no fine detail. The blurred image is subtracted from the original
to extract the fine detail. This fine detail is then added to the
original image to highlight complex areas.
The radius parameter determines the radius of the Gaussian Blur
in pixels and lets you choose the level of scale of detail that
should be enhanced. The difference between color levels on the blurred
and original image is determined at each point on the image. If
the difference is greater than the Threshold parameter then the
Amount percentage of the difference is added back to the original
image.
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