[Insight-users] Help with boundary conditions in itkBSplineInterpolateImageFunction

[Monica Hernandez Gimenez]

Dear itk users,

I am trying to use itkBSplineInterpolateImageFunction to perform the
composition of a function in a regular grid deformed by some
transformation. However, mirror boundary conditions are totally wrong
for my application and this is the only option provided by the class.

I have experienced with Matlab interp2 function

fI = interp2( X, Y, f, XI, YI, 'spline' )

where X and Y represent the regular grid,
XI and YI represent the deformed grid
f is the function I am interested in interpolating. In this case,
boundary conditions seem to be really OK for my application.

I have tried very hard to understand how bspline interpolation in
Matlab deals with pixels in the boundary in order to include it in  
itkBSplineInterpolateFunction, regretfuly I was not able to understand
the code. It seems that both interpolation and extrapolation is
performed at the same time in splncore.m file.

Could anybody help me to understand the extrapolation method used
in matlab in order to include it in itkBSplineInterpolateImageFunction?

Does anybody know if splncore.m code is implemented somewhere in C
like language? (I think this also may help a lot)

Thanks a lot!

Monica.