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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<h1 id="firstHeading" class="firstHeading">Dust Removal with Flatfield</h1>
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<p>Dust can get into camera optics. In panorama images created from such photos the repetitive pattern can be particulary irritating, as a dust speck or a dust speck pattern tends to show up multiple times.
</p>
<div class="thumb tright"><div class="thumbinner" style="width:602px;"><img alt="" src="600px-Tuebingen_Neckarfront_withdustspots_small15_2006-06-11.jpg" width="600" height="166" border="0" class="thumbimage" /><a class="external" href="http://wiki.panotools.org/File:Tuebingen_Neckarfront_withdustspots_small15_2006-06-11.jpg">[*]</a> <div class="thumbcaption"><div class="magnify"><img src="http://wiki.panotools.org/wiki/skins/common/images/magnify-clip.png" width="15" height="11" alt="" /><a class="external" href="http://wiki.panotools.org/File:Tuebingen_Neckarfront_withdustspots_small15_2006-06-11.jpg">[*]</a></div>Image with dust specks</div></div></div>
<p>One can prepare a flatfield for correction. While one may correct the input files prior to stitching precessing each with the <i>gimp</i> for example, a much smoother workflow results if the stitching software itself provides for the use of a flatfield.
</p>
<div class="thumb tright"><div class="thumbinner" style="width:602px;"><img alt="" src="600px-Tuebingen_Neckarfront_small15_2006-06-11.jpg" width="600" height="186" border="0" class="thumbimage" /><a class="external" href="http://wiki.panotools.org/File:Tuebingen_Neckarfront_small15_2006-06-11.jpg">[*]</a> <div class="thumbcaption"><div class="magnify"><img src="http://wiki.panotools.org/wiki/skins/common/images/magnify-clip.png" width="15" height="11" alt="" /><a class="external" href="http://wiki.panotools.org/File:Tuebingen_Neckarfront_small15_2006-06-11.jpg">[*]</a></div>Image without dust specks</div></div></div>
<p>Flatfields may also be used to correct <a href="Vignetting.html" title="Vignetting">vignetting</a>, or vignetting correction and dust removal combined. But even with hugin 0.7 using a parametrisation approach for vignetting, a suitably prepared flatfield is useful for dust removal.<br style="clear:both;" />
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<a name="Example_of_flatfield_performance" id="Example_of_flatfield_performance"></a><h2> <span class="mw-headline"> Example of flatfield performance </span></h2>
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<div class="thumb" style="padding: 28px 0; width: 150px;"><div style="margin-left: auto; margin-right: auto; width: 120px;"><img alt="" src="120px-Flatfield3_Munich.jpg" width="120" height="90" border="0" /><a class="external" href="http://wiki.panotools.org/File:Flatfield3_Munich.jpg">[*]</a></div></div>
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<p>Original image
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<p>Snapped raw flatfield
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<p>Flatfield
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<p>Corrected image
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<p>Leftmost in the gallery a photo with dust in the lense. Here it is rather visible,
as my camera sometimes had the habit of showing a focussed image
of the dust specks as well. I have downscaled the images.
</p><p>Shortly later the camera fell into that habit again, and I had a
whiteboard nearby, so I set the lense aperture to the same value
and took a photo of the featureless whiteboard.
It is rather dark, but it shows the same dust specks
as the photo I want to correct.
</p><p>After some brightness adjustment and blurring (details on request)
with the gimp the thrid images is now the flatfield as used in the layer
with the mode set to "divide".
</p><p>Rightmost the corrected photo. If one looks closely I did not get
the flatfield completely right in the upper half of the image,
as the white in the flatfield is blown the dust specks in the sky are under-corrected.
See in particular the top left corner. with a little more time
I probably could produce a better flatfield version. But the specks
on the runway are pretty much gone.
</p><p>This example is shown with a view towards hugin, where in hugin 0.6beta
flatfield image was available but hugin 0.7beta5 does no longer have it in the GUI.
In particular within a panorama stitch the dust specks have the nasty habit of showing up
several times and forming a repetitive pattern which your eye
is faster to spot than a single spot positioned at random.
</p>
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