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<h2 class="title" style="clear: both"><a id="filters-blur"></a>2. Blur filters</h2>
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<div class="sect2" lang="en" xml:lang="en">
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<h3 class="title"><a id="filters-blur-introduction"></a>2.1. Blur filters introduction</h3>
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<div class="informalfigure">
<div class="mediaobject">
<img src="../images/filters/examples/blur-demo-orig.png" />
<div class="caption">
<p>
Original for demo
</p>
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<p>
This is a set of filters that blur images, or parts of them,
in various ways. If there is a selection, only the selected parts
of an image will be blurred. There may, however, be some leakage
of colors from the unblurred area into the blurred area. To help
you pick the one you want, we will illustrate what each does when
applied to the image shown at right. These are, of course, only
examples: most of the filters have parameter settings that allow
you to vary the magnitude or type of blurring.
</p>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/filters/examples/blur-demo-gauss10.png" />
<div class="caption">
<p>
Gaussian blur (radius 10)
</p>
</div>
</div>
</div>
<p>
The most broadly useful of these is the Gaussian blur. (Don't let
the word "Gaussian" throw you: this filter makes an image blurry
in the most basic way.) It has an efficient implementation that
allows it to create a very blurry blur in a relatively short
time.
</p>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/filters/examples/blur-demo-blur.png" />
<div class="caption">
<p>
Simple blur
</p>
</div>
</div>
</div>
<p>
If you only want to blur the image a little bit--to
soften it, as it were--you might use the simple "Blur" filter. In
Gimp 2.2 this runs automatically, without creating a dialog. The
effect is subtle enough that you might not even notice it, but you
can get a stronger effect by repeating it. In Gimp 2.0 the filter
shows a dialog that allows you to set a "repeat count".
If you want a strong blurring effect, this filter
is too slow to be a good choice: use a Gaussian blur instead.
</p>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/filters/examples/blur-demo-selective.png" />
<div class="caption">
<p>
Selective blur
</p>
</div>
</div>
</div>
<p>
The Selective Blur filter allows you to set a threshold so that
only pixels that are similar to each other are blurred together.
It is often useful as a tool for reducing graininess in photos
without blurring sharp edges. (In the example, note that the
graininess of the background has been reduced.) The
implementation is much slower
than a Gaussian blur, though, so you should not use it unless you
really need the selectivity.
</p>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/filters/examples/blur-demo-pixelize.png" />
<div class="caption">
<p>
Pixelize
</p>
</div>
</div>
</div>
<p>
The Pixelize filter produces the well-known "Abraham Lincoln"
effect by turning the image into a set of large square pixels.
(The <a href="ch06s11s07.html" title="11.7. Oilify">Oilify</a> filter, in
the Artistic Filters group, has a similar effect, but with
irregular blobs instead of perfectly square pixels.)
</p>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/filters/examples/blur-demo-mblur.png" />
<div class="caption">
<p>
Motion blur
</p>
</div>
</div>
</div>
<p>
The Motion Blur filter blurs in a specific direction at each
point, which allows you to create a sense of motion: either
linear, radial, or rotational.
</p>
<p>
Finally, the Tileable Blur filter is really the same thing as a
Gaussian blur, except that it wraps around the edges of an image
to help you reduce edge effects when you create a pattern by
tiling multiple copies of the image side by side.
</p>
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<p>
Tileable Blur is actually implemented by a Script-Fu script that
invokes the Gaussian blur plug-in.
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