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<h3 class="title"><a id="plug-in-dog"></a>5.3. Difference of Gaussians</h3>
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<p>
This filter is located at
<span class="guimenu">Filters</span>-><span class="guisubmenu">Edge detect</span>-><span class="guimenuitem">Difference of Gaussians</span>
</p>
<p>
Le filtre se trouve à
<span class="guimenu">Filtres</span>-><span class="guisubmenu">Détection de bord</span>-><span class="guimenuitem">Différence gaussienne</span>
</p>
<p>
This filter is new in GIMP 2.2. It does edge detection using
the so-called "Difference of Gaussians" algorithm, which works
by performing two different Gaussian blurs on the image, with a
different blurring radius for each, and subtracting them to
yield the result. This algorithm is very widely used in
artificial vision (maybe in biological vision as well!), and is
pretty fast because there are very efficient methods for doing
Gaussian blurs. The most important parameters are the blurring
radii for the two Gaussian blurs. It is probably easiest to set
them using the preview, but it may help to know that increasing
the smaller radius tends to give thicker-appearing edges, and
decreasing the larger radius tends to increase the "threshold"
for recognizing something as an edge. In most cases you will
get nicer results if Radius 2 is smaller than Radius 1, but
nothing prevents you from reversing them, and in
situations where you have a light figure on the dark background,
reversing them may actually improve the result.
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<h4 class="title"><a id="id3362178"></a>Options</h4>
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<dt>
<span class="term">Smoothing parameters</span>
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<dd>
<p>
Radius 1 and Radius 2 are the blurring radii for the two
Gaussian blurs. The only constraints on them is that they
cannot be equal, or else the result will be a blank
image. If you want to produce something that looks like a
sketch, in most cases setting Radius 2 smaller than
Radius 1 will give better results.
</p>
</dd>
<dt>
<span class="term">Normalize</span>
</dt>
<dd>
<p>
Checking this box causes the brightness range in the
result to be stretched as much as possible. Note that in
the preview, only the part of the image that is shown is
taken into account, so with "Normalize" checked the
preview is not completely accurate. (It is accurate
except in terms of global contrast, though.)
</p>
</dd>
<dt>
<span class="term">Invert</span>
</dt>
<dd>
<p>
Checking this box inverts the result, so that you see dark
edges on a white background, giving something that looks
more like a drawing.
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