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<font size=3>But can't you use it for upsampling the CoefficientImage of
the BSplineDeformableTransform?<br><br>
However, you are right that it will not give exactly the same deformation
field. As I understood from reading the code, the (3rd order)
BSplineDeformableTransform uses a kind of approximating spline. So,
simply upsampling the CoefficientImage will indeed change the deformation
field (it will make it more 'interpolating'). <br><br>
But anyway, wouldn't it be a fair approximation to just upsample the
coefficient image? In fact, I do it like this, and it does work. In
practice the introduced error will be small, i think. <br><br>
Regards,<br>
Stefan.<br><br>
<br>
At 10:25 23/07/04, Miller, James V (Research) wrote:<br>
</font><blockquote type=cite class=cite cite><font face="verdana" size=2 color="#0000FF">I
think the BSplineUpsampleImageFilter upsamples an image via B-spline
interpolation. I think Karl wants to "upsample" his B-spline
not an image.</font><font size=3><br>
<br>
</font><font face="verdana" size=2 color="#0000FF">Jim</font><font size=3><br>
</font>
<dl>
<dd><font face="tahoma" size=2>-----Original Message-----<br>
<dd>From:</b> Stefan Klein
[<a href="mailto:stefan@isi.uu.nl" eudora="autourl">mailto:stefan@isi.uu.nl</a>]<br>
<dd>Sent:</b> Friday, July 23, 2004 9:21 AM<br>
<dd>To:</b> insight-users@itk.org<br>
<dd>Subject:</b> RE: [Insight-users] increasing bspline control point
density<br><br>
</font>
<dd><font size=3>Hi Karl,<br><br>
<dd>You may use the itk::BSplineUpsampleImageFilter.<br>
<dd>Look at the help of itk::BSplineUpsampleImageFilterBase. There it's
explained how it works.<br><br>
<dd>Regards,<br>
<dd>Stefan.<br><br>
<br><br>
<br>
<dd>At 08:46 23/07/04, Miller, James V (Research) wrote:<br>
<blockquote type=cite class=cite cite>
<dd>I do not think ITK provides a mechanism for increasing the number of
<br>
<dd>control points in a B-spline grid. However, the mathematics of
B-splines<br>
<dd>do support this operation. There are formulas for adding a
control point<br>
<dd>to a B-spline that maintain the trace of the B-spline (shape of
the<br>
<dd>B-spline).<br><br>
<dd>Any good book on B-splines will provide the formulas. <br><br>
<dd>Jim<br><br>
<br><br>
<dd>-----Original Message-----<br>
<dd>From: Karl Baum
[<a href="mailto:kgbaum@syr.edu" eudora="autourl">mailto:kgbaum@syr.edu</a>]<br>
<dd>Sent: Thursday, July 22, 2004 5:22 PM<br>
<dd>To: insight-users@itk.org<br>
<dd>Subject: [Insight-users] increasing bspline control point
density<br><br>
<br>
<dd>Hi,<br>
<dd>I am using BSplines to provide the transformations necessary for
my<br>
<dd>registration. I would like to take an iterative approach where
I first do<br>
<dd>registration with a low control point density, and then use the
results as<br>
<dd>input to a registration with a higher control point density.
The issue I am<br>
<dd>facing at this point in time is how to initialize the parameters of
the<br>
<dd>second iteration with the results of the first iteration. In
other words I<br>
<dd>need to take the grid defined by the deformation coefficients of the
first<br>
<dd>iteration, and use it as input into the second. To do this I
need to<br>
<dd>calculate the starting deformation coefficients on the higher density
grid. <br><br>
<dd>Does itk provide anything to do this? I was unable to find
any<br>
<dd>documentation addressing this.<br><br>
<dd>Thanks,<br>
<dd>Karl<br><br>
<br>
<dd>_______________________________________________<br>
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<dd>Insight-users@itk.org<br>
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<dd>_______________________________________________<br>
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<dd>Insight-users@itk.org<br>
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</blockquote></font>
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