Figure 16.2. Original for demo
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.
Figure 16.3. Gaussian blur (radius 10)
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
If you only want to blur the image a little bit — to soften it, as it were —
you might use the simple "Blur" filter. This filter 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.
Figure 16.5. Selective blur
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.
The Pixelize filter produces the well-known "Abraham Lincoln"
effect by turning the image into a set of large square pixels.
(The Oilify filter, in
the Artistic Filters group, has a similar effect, but with
irregular blobs instead of perfectly square pixels.)
You can find a nice explanation of the Abraham Lincoln effect
at [BACH04]. You will see the
Salvador Dali's painting “Gala Contemplating the
Mediterranean Sea” turning to an Abraham Lincoln's portrait
when looking at it from a distance.
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
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.
Tileable Blur is actually implemented by a Script-Fu script that invokes
the Gaussian blur plug-in.