[Insight-users] increasing bspline control point density

[Stefan Klein]

But can't you use it for upsampling the CoefficientImage of the 
BSplineDeformableTransform?

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').

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.

Regards,
Stefan.


At 10:25 23/07/04, Miller, James V (Research) wrote:
>I think the BSplineUpsampleImageFilter upsamples an image via B-spline 
>interpolation. I think Karl wants to "upsample" his B-spline not an image.
>
>Jim
>-----Original Message-----
>From: Stefan Klein [mailto:stefan at isi.uu.nl]
>Sent: Friday, July 23, 2004 9:21 AM
>To: insight-users at itk.org
>Subject: RE: [Insight-users] increasing bspline control point density
>
>Hi Karl,
>
>You may use the itk::BSplineUpsampleImageFilter.
>Look at the help of itk::BSplineUpsampleImageFilterBase. There it's 
>explained how it works.
>
>Regards,
>Stefan.
>
>
>
>
>At 08:46 23/07/04, Miller, James V (Research) wrote:
>>I do not think ITK provides a mechanism for increasing the number of
>>control points in a B-spline grid.  However, the mathematics of B-splines
>>do support this operation.  There are formulas for adding a control point
>>to a B-spline that maintain the trace of the B-spline (shape of the
>>B-spline).
>>
>>Any good book on B-splines will provide the formulas.
>>
>>Jim
>>
>>
>>
>>-----Original Message-----
>>From: Karl Baum [mailto:kgbaum at syr.edu]
>>Sent: Thursday, July 22, 2004 5:22 PM
>>To: insight-users at itk.org
>>Subject: [Insight-users] increasing bspline control point density
>>
>>
>>Hi,
>>I am using BSplines to provide the transformations necessary for my
>>registration.  I would like to take an iterative approach where I first do
>>registration with a low control point density, and then use the results as
>>input to a registration with a higher control point density.  The issue I am
>>facing at this point in time is how to initialize the parameters of the
>>second iteration with the results of the first iteration.  In other words I
>>need to take the grid defined by the deformation coefficients of the first
>>iteration, and use it as input into the second.  To do this I need to
>>calculate the starting deformation coefficients on the higher density grid.
>>
>>Does itk provide anything to do this?  I was unable to find any
>>documentation addressing this.
>>
>>Thanks,
>>Karl
>>
>>
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