[ITK] About pipeline recursion

[Bradley Lowekamp]

Hello,

There is some code in the pipeline architecture to prevent circular execution. I believe it has been used for more complex circular pipelines. But your case is a bit simplified and has a problem.

For your particular case the input image IS same as the output image. This does not surprise me that it breaks things and causes odd behavior.

I am not sure if the below pipeline is close to what you are trying to do in the end or not. But I'll suggest the following:

1) After getting the output, call tmpImage->DisconnectPipeline().
This will explicitly sever the pipeline, and allow you to manual place the output as a input.

2) Turn on InPlace for the AddImageFilter.
 This will copy the buffer of input1 to the output and remove the need to allocate a new output.

Hope that helps,
Brad

On Jun 20, 2014, at 4:35 AM, Nicolas Gallego <nicgallego at gmail.com> wrote:

> Good morning,
> 
> I have been coding a filter that implements an iterative procedure on images. I have tried the straight forward implementation of updating a temporal image on the recursion loop but results are wrong. The correct result is obtained when I explicitly unroll the pipeline although it becomes harder to code for more complex pipelines, and I am concerned about the scalability on the number of recursions.
> 
> Could you give me some ideas to work this point out. Is there a way to implement a straight forward way in itk? Here the code that illustrates the point on recursively adding images:
> 
> ----- code 1 -------------
>         std::cout << "Recursion on image pointer" << std::endl;
>     ImageType::Pointer image1 = ImageType::New();
>     image1->SetRegions( region );
>     image1->Allocate();
>     image1->FillBuffer( 1 );
>     AdderType::Pointer adder = AdderType::New();
>     adder->SetInput1( image1 );
>     adder->SetInput2( image1 );
>     adder->Update();
>     ImageType::Pointer tmpImage = adder->GetOutput();
>     std::cout << "start: " << image1->GetPixel( index ) << std::endl;
>     const unsigned short N = 10;
>     for ( unsigned short k = 0; k < N; k++ ) {
>         adder->Update();
>         tmpImage = adder->GetOutput();
>         std::cout << k << " " << tmpImage->GetPixel( index ) << std::endl;
>         adder->SetInput1( tmpImage );
>         adder->SetInput2( image1 );
>     }
>     std::cout << std::endl;
> --- end of 1 --------------
> 
> Code 1 produces the following output:
> -----------------------------------------------
> Recursion on image pointer
> start: 1
> 0 2
> 1 3
> 2 3
> 3 3
> 4 4
> 5 4
> 6 4
> 7 5
> 8 5
> 9 5
> ---------------------------------------------
> 
> The explicit pipeline unroll is illustrated in code 2
> 
> --- code 2 -----------------------------------------------
> std::cout << "Pipeline explicit unroll recursion" << std::endl;
>     std::vector< AdderType::Pointer > adders( N );
>     adders[0] = AdderType::New();
>     adders[0]->SetInput1( image1 );
>     adders[0]->SetInput2( image1 );
>     std::cout << "start: " << image1->GetPixel( index ) << std::endl;
>     // connections
>     for ( unsigned short k = 1; k < N; k++ ) {
>         adders[k] = AdderType::New();
>         adders[k]->SetInput1( adders[k-1]->GetOutput() );
>         adders[k]->SetInput2( image1 );
>     }
>     // execution
>     adders[N-1]->Update();
>     for ( unsigned short k = 0; k < N; k++ ) {
>         std::cout << k  << " " << adders[k]->GetOutput()->GetPixel( index ) << std::endl;
>     }
> 
> --- end of code 2 --------------------------------------
> 
> Pipeline explicit unroll recursion
> start: 1
> 0 2
> 1 3
> 2 4
> 3 5
> 4 6
> 5 7
> 6 8
> 7 9
> 8 10
> 9 11
> ------------------------------------
> 
> Find attached complete code file, thank you for your help
> 
> ------
> Nicolás Gallego-Ortiz
> Université catholique de Louvain, Belgium
> <recursionTest.cxx>_______________________________________________
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