[Insight-developers] RecursiveGaussianImageFilter

[Luis Ibanez]

Hi Gunnar,

Thanks for posting the solution to this problem.

We are running an experimental build on Linux in order to
test your changes, and if everything goes well, they will
get commited into CVS.

Your suggestion of adding a method for managing the boundary
condition sounds like a good idea.

We may want to start with a simple option for Zero padding,
although you may want to take a look at how boundary conditions
are managed by the neighbor iterators, maybe we can reuse the
same approach.


   Thanks again for posting your code,



     Regards,


        Luis



-----------------------------------------
Gunnar Farneback wrote:

> I have made some changes to the recursive Gaussian filter, described
> at http://lmi.bwh.harvard.edu/~gunnar/itk_recursive_gaussian.html.
> 
> This changes the filter responses in two important respects:
> 
> 1. The derivative filters become exactly (down to machine precision)
>    invariant to addition of constants, solving bug #584.
> 2. The scaling of the filter responses is modified so that the
>    derivative of n is exactly 1 and the second derivative of n^2 is
>    exactly 2. (See also the figure on the referenced web page.)
> 
> The computational structure and complexity are unchanged, as is the
> interface to the class.
> 
> I have changed the behavior of the filters in one place. Currently the
> filter results are negated if the image spacing is negative. This
> seems reasonable for the first derivative filter but it doesn't make
> any sense to me for the smoothing filter and the second derivative
> filter. Am I correct in assuming that this is a bug and not intended
> behavior?
> 
> A second observation is that the recursive Gaussian filter is
> hardcoded with the edge extension boundary condition. In some
> situations it is necessary to have the zero padding boundary
> condition, in order for the filter results to be useful. Would it be
> an acceptable solution to add a method to choose between these
> boundary conditions? Implementing support for zero padding is not
> difficult but other boundary conditions may be quite tricky.
> 
> /Gunnar
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