[Insight-developers] SubtractImageFilter strange behavior ?

[Gaetan Lehmann]

I haven't attached the image to the mail because it is rejected by the  
list with it.
You can get it at http://voxel.jouy.inra.fr/gradient.png

On Wed, 16 Nov 2005 18:04:21 +0100, Gaetan Lehmann  
<gaetan.lehmann at jouy.inra.fr> wrote:

>
> Hi,
>
> I have done a morphological gradient image filter in which I use a  
> SubtractImageFilter. Everything seems to work fine, but
> when  I tried to remove the subtract filter and do the subtraction by  
> hand, I don't get the same result.
>
> This part of code:
>
>    // Need to subtract the eroded image from the dialted one
>    typename SubtractImageFilter<TInputImage, TInputImage,  
> TOutputImage>::Pointer
>      subtract=SubtractImageFilter<TInputImage,TInputImage,TOutputImage>::New();
>    subtract->SetInput1( dilate->GetInput() );
>    subtract->SetInput2( erode->GetOutput() );
>
>    // graft our output to the subtract filter to force the proper regions
>    // to be generated
>    subtract->GraftOutput( this->GetOutput() );
>
>    progress->RegisterInternalFilter(subtract,.1f);
>
>    dilate->Update(); // needed to have the right progress values
>    subtract->Update();
>
>    // graft the output of the subtract filter back onto this filter's
>    // output. this is needed to get the appropriate regions passed
>    // back.
>    this->GraftOutput( subtract->GetOutput() );
>
>
> and this one
>
>    dilate->Update();
>    erode->Update();
>
>    const TInputImage* inputPtr1 = dilate->GetOutput();
>    const TInputImage* inputPtr2 = erode->GetOutput();
>    const TInputImage* inputPtr = this->GetInput();
>    TOutputImage* outputPtr = this->GetOutput();
>
>    ImageRegionConstIterator<TInputImage> inputIt1(inputPtr1,  
> inputPtr->GetRequestedRegion());
>    ImageRegionConstIterator<TInputImage> inputIt2(inputPtr2,  
> inputPtr->GetRequestedRegion());
>
>    ImageRegionIterator<TOutputImage> outputIt(outputPtr,  
> inputPtr->GetRequestedRegion());
>
>    inputIt1.GoToBegin();
>    inputIt2.GoToBegin();
>    outputIt.GoToBegin();
>
>    while( !inputIt1.IsAtEnd() )
>      {
>      outputIt.Set( static_cast< typename TOutputImage::PixelType
> ( inputIt1.Get() - inputIt2.Get() ) );
>      ++inputIt2;
>      ++inputIt1;
>      ++outputIt;
>      }
>
>
> does not produce the same output.
>
> Am I doing something wrong ?
> Or is it a problem in SubtractImageFilter ?
>
> Attached gradient.png is the result with the subtract filter.
> http://voxel.jouy.inra.fr/darcs/contrib-itk/gradient/gradient.png is the  
> result without the subtract filter.
> The full code is available at  
> http://voxel.jouy.inra.fr/darcs/contrib-itk/gradient/
>
> Regards,
>
> Gaetan
>



-- 
Gaëtan Lehmann
Biologie du Développement et de la Reproduction
INRA de Jouy-en-Josas (France)
tel: +33 1 34 65 29 66    fax: 01 34 65 29 09
http://voxel.jouy.inra.fr