[Insight-users] ConfidenceFilter
Miller, James V (Research)
millerjv@crd.ge.com
Tue, 28 Jan 2003 09:45:20 -0500
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I think it is possible for this to happen. I was actually worried =
about this. If the statistics
after the first iteration no longer include the seed point, then second =
iteration will result in no
segmentation. Multiplier=3D1 is rather small, as it will only include =
63% of the pixels whose
intensities "probably" are the same intensity. Another way to look at =
this is that after the initial
iteration, you have a 37% chance the seed point would not belong to the =
statistics of the segmented
region.
=20
To finesse this, you might try starting with a larger radius and a =
larger multiplier. I usually run
with a multiplier of 2.5 or so. Using the above analogy, there is less =
than a 1% chance the seed
pixel is outside the statistics of the region from the previous =
iteration.
=20
Now the reason for the problem exists: This is a simple segmentation =
filter that illustrates how the
flood fill iterator can be used to construct a simple but powerful =
segmentation filter. The actual
code for this algorithm is very very small. One of the things this =
filter "should" be doing is=20
seeding the second segmentation with the results of the first =
segmentation and continuing segmenting
the image using the refined statistics. At the time this filter was =
written - and I am not sure
whether this has changed - you could not seed the flood fill iterators =
with multiple seed points. So
my only option was to rewind to the initial seed point and start the =
segmentation process again using
the refined statistics. Otherwise, the algorithm would not revisit a =
pixel that was excluded on an
initial iteration in a subsequent iteration.
=20
I just looked at the iterator code and there is now a method that =
allows you to specify a=20
vector of seeds. So the algorithm could be rewritten to allow the =
segmentation from one iteration to
be the seed at another iteration. I would probably put this in as a =
mode as someone may want the
initial behavior.
=20
Other than that, I am not sure of a good way to address the problem if =
the statistics of the segment
stray such they exclude the seed point. I suppose we could search for a =
pixel near the seed point
that is within the statistics of the initial segment and use that =
position as the seed for the next
iteration. This would probably be constrained such that the point was =
near the initial seed AND the
point statisfies the statistics from the previous iteration AND the =
point was in the segmentation
from the previous iteration. Intuitively, that makes sense to me.
=20
=20
=20
-----Original Message-----
From: Samuel Rodr=EDguez Bescos [mailto:srodrigu@gbt.tfo.upm.es]
Sent: Tuesday, January 28, 2003 4:35 AM
To: insight-users@public.kitware.com
Subject: [Insight-users] ConfidenceFilter
Hi!!
=20
I think that the confidence filter has got a strange behaviour. I set =
the next the parameters :
Initial Radious=3D1, Multipler=3D1.0 and iterations 1 and the filter =
works well. But when I increase the
iterations, the filter doesn't select any zone of the image.
=20
is that could be possible?.
=20
Thnks!!
=20
Sam
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<DIV><SPAN class=194052214-28012003><FONT color=#0000ff size=2>I think it is
possible for this to happen. I was actually worried about this. If the
statistics after the first iteration no longer include </FONT></SPAN><SPAN
class=194052214-28012003><FONT color=#0000ff size=2>the seed point, then second
iteration will result in no segmentation. Multiplier=1 is rather small,
</FONT></SPAN><SPAN class=194052214-28012003><FONT color=#0000ff size=2>as it
will only include 63% of the pixels whose intensities "probably" are the same
intensity. Another way to look at this is that after the initial
iteration, you have a 37% chance the seed point would not belong to the
statistics of the segmented region.</FONT></SPAN></DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff size=2>To finesse this,
you might try starting with a larger radius and a larger multiplier. I
usually run </FONT></SPAN><SPAN class=194052214-28012003><FONT color=#0000ff
size=2>with a multiplier of 2.5 or so. Using the above analogy, there is less
than a 1% chance the seed pixel is outside the statistics of the region
from the previous iteration.</FONT></SPAN></DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff size=2>Now the reason
for the problem exists: This is a simple segmentation filter that illustrates
how the flood fill iterator can be used to construct a simple but powerful
segmentation filter. The actual code for this algorithm is very very
small. One of the things this filter "should" be doing is
</FONT></SPAN></DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff size=2>seeding the
second segmentation with the results of the first segmentation and continuing
segmenting the image using the refined statistics. At the time this filter
was written - and I am not sure whether this has changed - you could not seed
the flood fill iterators with multiple seed points. So my only option was
to rewind to the initial seed point and start the segmentation process again
using the refined statistics. Otherwise, the algorithm would not revisit a
pixel that was excluded on an initial iteration in a subsequent
iteration.</FONT></SPAN></DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff size=2>I just looked at
the iterator code and there is now a method that allows you to specify a
</FONT></SPAN></DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff size=2>vector of
seeds. So the algorithm could be rewritten to allow the segmentation from
one iteration to be the seed at another iteration. I would probably put this in
as a mode as someone may want the initial behavior.</FONT></SPAN></DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff size=2>Other than that,
I am not sure of a good way to address the problem if the statistics of the
segment stray such they exclude the seed point. I suppose we could search for a
pixel near the seed point that is within the statistics of the initial segment
and use that position as the seed for the next iteration. This would probably be
constrained such that the point was near the initial seed AND the point
statisfies the statistics from the previous iteration AND the point was in the
segmentation from the previous iteration. Intuitively, that makes sense to
me.</FONT></SPAN><SPAN class=194052214-28012003><FONT color=#0000ff
size=2></FONT></SPAN></DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=194052214-28012003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px solid; MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> Samuel Rodríguez Bescos
[mailto:srodrigu@gbt.tfo.upm.es]<BR><B>Sent:</B> Tuesday, January 28, 2003
4:35 AM<BR><B>To:</B> insight-users@public.kitware.com<BR><B>Subject:</B>
[Insight-users] ConfidenceFilter<BR><BR></FONT></DIV>
<DIV><FONT face=Arial size=2>Hi!!</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I think that the confidence filter has got a
s</FONT><FONT face=Arial size=2>trange behaviour. I set the next the
parameters : Initial Radious=1, Multipler=1.0 and iterations 1 and the filter
works well. But when I increase the iterations, the
filter doesn't select any zone of the image.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>is that could be possible?.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Thnks!!</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Sam</FONT></DIV></BLOCKQUOTE></BODY></HTML>
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