[Insight-users] periodic boundary conditions and recursive gaussian filter

[Jan Ehrhardt]

Hi Luis,

thanks for your answer. Enlarging the filter array in the recursive 
filter appears to me the fastest way to solve my problem and I think is 
a good approximation to the correct periodic filtering.

Is there another (more simple) way for a periodic convolution with a 
gaussian derivative? I can use the itkGaussianOperator for smoothing, 
but actual I see no way to convolve an image with a gaussian derivative 
using periodic boundary conditions, without writing my own filter class.

I found the classes itkGaussianDerivativeImageFunction 
<cid:part1.07090305.03050509 at uke.uni-hamburg.de> and 
itkGaussianDerivativeSpatialFunction 
<cid:part2.03010205.09020608 at uke.uni-hamburg.de> but I don't know how to 
use these classes for filtering. Can you give me a short hint?

Thanks and regards,

Jan

Luis Ibanez wrote:

>
> Hi Jan,
>
>
>
>    Yes, It is possible   :-)
>
>
>    But, It is not implemented.
>
>
>
> This is a non-trivial task. In order to implement periodic
> boundary conditions you will have to get familiar with the
> computation of the coefficients for the IIR filters that are
> used in the Recursive Gaussian Filter.
>
> Note that it is not as simple as enlarging the array and
> tricking the filter by suffing the replicated values, because
> this filter is not using a finite support for a convolution
> kernel. This filter actually approximates an infinite support
> kernel.
>
>
> This can well be a semester project for a student
> in a signal processing class.
>
>
> ---
>
> About the Doxygen question, what happens is the our use of
> Generic Programming makes harder for Doxygen to figure out
> all the inheritance relationships.
>
>
> One way of getting a full list of derived classes is by using
> SourceNavigator
>
>          http://sourcenav.sourceforge.net/
>
> This nice application builds a full database of a software
> project and helps you browse the code by finding all the
> variables, types, functions, classes and header relationships.
>
>
>
>
>     Regards,
>
>
>
>       Luis
>
>
>
>
> -------------------
> Jan Ehrhardt wrote:
>
>> Hi,
>>
>> is it possible to get periodic boundary conditions for the 
>> RecursiveGaussianImageFilter (or more general for
>> RecursiveSeparableImageFilters) ?
>> Specifically, I want to calculate the gradient (with a gaussian 
>> derivative) of an image with periodic boundary conditions in 
>> z-direction and neumann conditions in x/y-direction. In the next 
>> step, I want to apply gaussian smoothing to a N-dimensional 
>> vector-field with periodic boundary conditions in z-direction and 
>> neumann conditions in x/y-direction.
>>
>> One idea is to reimplement RecursiveSeparableImageFilters and to 
>> enlarge the array given to FilterDataArray (..). But how many values 
>> I have to add?
>>
>> Another small problem: the doxygen documentation don't lists all  
>> subclasses in the inheritance diagramm. How can I get a list of _all_ 
>> subclasses e.g. of the ImageToImageFilter ?
>>
>> Thanks,
>>
>> Jan
>>
>>
>>
>>
>> _______________________________________________
>> Insight-users mailing list
>> Insight-users at itk.org
>> http://www.itk.org/mailman/listinfo/insight-users
>>
>>
>
>