Download title: GNU Image Manipulation Program subtitle: User Manual

Overview
This filter is found in Image>Filters/Enhance/Sharpen
Most of digitized images need correction of sharpness. This is due to digitizing process
that must chop a color continuum up in points with slightly different colors: elements
thiner than sampling frequency will be averaged into an uniform color. So sharp borders
are rendered a little blurred. The same phenomenon appears when printing color dots on
paper.
The Sharpen filter accentuates edges but also any noise or blemish and it may create
noise in graduated color areas like the sky or a water surface. It competes with the
Unsharp Mask filter, which is more sophisticated and renders more natural results.
Options
Out-of-focus photographs and most digitized images often need a sharpness correction.
This is due to the digitizing process that must chop a color continuum up in points with
slightly different colors: elements thinner than sampling frequency will be averaged into
an uniform color. So sharp borders are rendered a little blurred. The same phenomenon
appears when printing color dots on paper.
The Unsharp Mask filter (what an odd name!) sharpens edges of the elements without
increasing noise or blemish. It is the king of the sharpen filters.
Some scanners apply a sharpen filter while scanning. It's worth disabling it so that you
keep control on your image.
GNU Image Manipulation Program
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This filter is found in Image>Filters/Enhance/Unsharp Mask
G e n e r a t e d
Overview
d o c b o o k 2 o d f
Unsharp Mask