[Insight-developers] RequestedRegion are modified when calling itk filters

[Karthik Krishnan]

Arnaud Garcia wrote:

> Hi itk developers,
>
> It seems that most itk filters change the RequestedRegion when calling 
> them ...
> Some filters overide  the GenerateInputRequestedRegion with  something 
> like:
>
> SetRequestedRegion( input->GetLargestPossibleRegion() );
>
>
>
> => So if you set your requested region and call such filters you have 
> to set it again after calling theses filters ...
>
> is it right ?
>
Yes. This is the expected behaviour since if you use such a filter in a 
pipeline and the filter needs the whole input to process, it must make 
such a request to those filters on its upstream. That said, such a 
request will not be propagated downstream. For instance if you use

A --> B --> C
and B needs the whole input to process.

C->SetRequestedRegion( ... )
C->Update();

This should set the requested regions of A's input and B's input to the 
whole image, but C's input's requested region should stay unchanged.

That said, there are a good number of filters that require the whole 
input to process, either because they do, or in some cases the filter is 
not well written to handle them.

For instance RecursiveSeparableGaussianFilter: I am not sure why the 
filter must make an assumption that it requires the entire input. It 
doesn't sound reasonable. Maybe the others have something to say about it.

-karthik

> thanks for answer,
>
> Arnaud
>
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