[Insight-users] slow itkConnectedComponentImageFilter and input RequestedRegion

[Richard Beare]

Hi,

Connected component labelling is one of those operations that needs
the entire image to be done correctly. The requested region idea in
ITK is for optimizing filters which can operate on small regions
independently, glue the results back together and end up with the same
result as if they'd processed the entire image at once - this is an
over simplified summary, but you get the idea. It makes certain types
of multithreading really easy. Pixel wise operations are the prime
candidate. Connectivity based operations, like flooding and labelling
don't work this way.

So if you really want to operate on only a small part of the image
then your safest option is to extract it explicitly and feed it
through you pipeline.

On Tue, Jul 7, 2009 at 11:15 AM, asamwm<asamwm at gmail.com> wrote:
> Hi all,
> I noticed the above filter is slow, and when I call relabel,
> it is even slower although I am setting the requested region
> to a small 3D block at the input image before attaching
> it to  the connectedcomponentsfilter.
> So I looked at the itkConnectedComponentsImageFilter.txx
> and found what looks like it is getting LargestPossibleRegion
> and setting it back as the RequestedRegion
> from the input.
> Would someone please confirm that this is a bug?
>
> If it is not, please point me to what I am missing.
>
> Thanks
>
>
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