[Insight-users] how to ensure multi threading and best iterators

[Bill Lorensen]

If it were only that easy...

Multi-threading in itk is done within filters by breaking up an image
into multiple regions. Each thread will operate on a region. Your
operation looks similar to the BinaryFunctorImageFilter subclasses,
e.g. AddImageFilter.

Try creating your own filter by modifying AddImageFilter. The "meat"
of the filer is in operator().

Bill

On Tue, Sep 14, 2010 at 3:06 AM,  <devieill at irit.fr> wrote:
> Hi all,
> I am trying to issue some trivial bench between blitz++ and itk since
> I wrote some code (optimization stuff : deconvolution RL-TV with non
> linear Conjugate Gradient method) and that my program is rather slow for
> 26M 3D images..
> So my question is  : assuming i have the following declarations and
> directives in a main.cxx file (see after), how can I be sure that what is
> inside the for statement will be executed with all the cores my computer
> have ?
> Although some cryptic compile options (e.g. -fununroll-loop
> -ftreevectorize) exist on gcc 4.4 I wonder if itk uses directly the
> multi-threading or if there exist a specific directive to enable it.
>
> On the other side I wonder if what I wrote is the fastest way to achieve a
> it3 = it1*log(1 + it2) computation, but to my knowledge there is no "array
> operations" in itk (maybe I am wrong or they are disguised).
>
> I would appreciate any comments/help regarding the multi-threading problem
> and the fast traversal of the 3D images.
>
> with kind regards,
> de Vieilleville François
>
>
> main.cxx
> ..
> typedef itk::Image<double, 3> WorkingImageType;
> typedef itk::ImageRegionIterator< WorkingImageType > ImageIteratorType;
> ..
> int main () {
> ..
> WorkingImageType::Pointer img1;
> WorkingImageType::Pointer img2;
> WorkingImageType::Pointer img3;
> ..
> // initialisation & fill of the 3 3D images
> ..
> ImageIteratorType it1( img1, img1->GetLargestPossibleRegion());
> ImageIteratorType it2( img2, img2->GetLargestPossibleRegion());
> ImageIteratorType it3( img3, img3->GetLargestPossibleRegion());
> ..
> for ( it1.GoToBegin(), it2.GoToBegin(), it3.GoToBegin(); !it3.IsAtEnd();
> ++it1, ++it2, ++it3)
> {
>      it3.Set( it1.Get()*log(1.0+it2.Get()));
> }
> ..
> }
>
>
>
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