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<h3 class="title"><a id="id3314809"></a>6.5. Removing Unwanted Objects from an Image</h3>
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<p>
There are two kinds of objects you might want to remove from an
image: first, artifacts caused by junk such as dust or hair on the
lens; second, things that were really present but impair the
quality of the image, such as a telephone wire running across the
edge of a beautiful mountain landscape.
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<h4 class="title"><a id="id3314510"></a>Despeckling</h4>
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<p>
A good tool for removing dust and other types of lens grunge
is the <a href="ch06s06s03.html" title="6.3. Despeckle">Despeckle</a>
filter, accessed as Filters->Enhance->Despeckle from the image
menu. Very important: to use this filter effectively, you
must begin by making a small selection containing the artifact
and a small area around it. The selection must be small
enough so that the artifact pixels are statistically
distinguishable from the other pixels inside the selection.
If you try to run despeckle on the whole image, you will
hardly ever get anything useful. Once you have created a
reasonable selection, activate Despeckle, and watch the
preview as you adjust the parameters. If you are lucky, you
will be able to find a setting that removes the junk while
minimally affecting the area around it. The more the junk
stands out from the area around it, the better your results
are likely to be. If it isn't working for you, it might be
worthwhile to cancel the filter, create a different selection,
and then try again.
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<p>
If you have more than one artifact in the image, it is
necessary to use Despeckle on each individually.
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<h4 class="title"><a id="id3315087"></a>Garbage Removal</h4>
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<p>
The most useful method for removing unwanted "clutter" from an
image is the <a href="ch03s03s08.html" title="3.8. Clone Tool">Clone</a>
tool, which allows you to paint over one part of an image
using pixel data taken from another part (or even from a
different image). The trick to using the clone tool
effectively is to be able to find a different part of the
image that can be used to "copy over" the unwanted part: if
the area surrounding the unwanted object is very different
from the rest of the image, you won't have much luck. For
example, if you have a lovely beach scene, with a nasty human
walking across the beach who you would like to teleport away,
you will probably be able to find an empty part of the beach
that looks similar to the part he is walking across, and use
it to clone over him. It is quite astonishing how natural the
results can look when this technique works well.
</p>
<p>
Consult the <a href="ch03s03s08.html" title="3.8. Clone Tool">Clone Tool
Help</a> for more detailed instructions. Cloning is as
much an art as a science, and the more you practice at it, the
better you will get. At first it may seem impossible to
produce anything except ugly blotches, but persistence will
pay off.
</p>
<p>
In some cases you may be able to get good results by simply
cutting out the offending object from the image, and then
using a plug-in called "Resynthesizer" to fill in the void.
This plug-in is not included with the main Gimp distribution,
but it can be obtained from the author's <a href="http://www.logarithmic.net/pfh/resynthesizer" target="_top">Resynthesizer</a>
web site. As with many things, your mileage may vary.
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<h4 class="title"><a id="id3315148"></a>Removing Red-eye</h4>
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<p>
When you take a flash picture of somebody who is looking
directly toward the camera, the iris of the eye can bounce the
light of the flash back toward the camera in such a way as to
make the eye appear bright red: this effect is called "red
eye", and looks very bizarre. Many modern cameras have special
flash modes that minimize red-eye, but they only work if you
use them, and even then they don't always work perfectly.
Interestingly, the same effect occurs with animals, but the
eyes may show up as other colors, such as green.
</p>
<p>
Gimp does not include a special tool for removing red-eye, but it
isn't all that hard to do. Basically the idea is to zoom the
area around the eye so that it is nice and large and easy to
work with; then make a selection of the red part of the eye
and a bit of the area around it; feather the selection so that
you don't create sharp-looking edges; and finally desaturate
the red channel inside the selection using one of the color
tools---Levels, Curves, or Hue/Saturation. It takes a little
practice the first few times, but once you have the technique
mastered, you should be able to quickly and easily create
quite a natural looking eye color.
</p>
<p>
If you would like a more automated approach, you can try
downloading a recently created <a href="http://registry.gimp.org/plugin?id=4212" target="_top">redeye</a>
plug-in from the Gimp Plug-in Registry. We have not received
any feedback so far about how well it works. It comes in
source code form, so you will need to be able compile it in
order to use it. (See <a href="ch02s08s03.html" title="8.3. Installing New Plugins">Installing New
Plug-ins</a> for information on how to do this.)
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