[Insight-users] Problem with Multiplying Two Complex Images, and a big thanks to ITK community for this extensive body of work!

[Luis Ibanez]

Hi Saurabh,

Please look at the example:

      Insight/Examples/Filtering/
          FFTImageFilterFourierDomainFiltering.cxx


It illustrates how to multiply the FFT of two images
in order to achieve in the frequency domain the
equivalent of convolution in the spatial domain.


    Regareds,


        Luis



---------------------
Saurabh Sethi wrote:
> Hi All,
> 
> I recently started using the ITK after a lot of word of mouth publicity 
> from peer groups :)
> 
> And I must say that im very impressed by it.
> 
> Have been going through all of the Software guide and Message Archives 
> since some time now.
> 
> I have a bit of problem with the FFT / IFFT implementation. There is 
> some "Access Violation" that I'm unable to fix since some time.
> 
> Maybe I have used the Complex Image in a wrong ( read Silly) way which 
> I'm unable to debug now.
> 
> It would be great if someone could help ->
> 
>  
> 
> I need to convolve two images (one is the test image, and other is my 
> data image)
> 
> For this, I had thought of first doing the FFT, then Multiplying both 
> the images and taking the IFFT in the end.
> 
>  
> 
> Here is my pseudo code:
> 
>  
> 
> read image 1 (im1)
> 
> Padd the image to nearest power of 2.
> 
> compute its FFT. (I'm using FFTRealToComplexConjugateImageFilter)
> 
>  
> 
> read image 2. (im2)
> 
> Padd the image to the same power of 2.
> 
> compute its FFT.
> 
>  
> 
> Multiply both the images
> 
> MultiplyImageFilter->SetInput1(fft_input);
> 
> MultiplyImageFilter->SetInput2(fft_weight);
> 
> MultiplyImageFilter->Update();
> 
>  
> 
> IT is here that this strange error occurs:
> 
>  
> 
> Unhandled exception at 0x0046193a in ItkScatter.exe: 0xC0000005: Access 
> violation reading location 0x61371000.
> 
>  
> 
> And the code breaks in at this place  in file 
> itkDefaultPixelAccessorFunctor.h:
> 
> inline const ExternalPixelType Get( const InternalPixelType & input ) const
> 
> {
> 
>    return m_PixelAccessor.Get( input );
> 
> }
> 
>  
> 
>  
> 
> Below is the relevant part of the code:
> 
>  
> 
> typedef itk::FFTRealToComplexConjugateImageFilter<pixelTypeC, dim2D> 
> FFTFilterType;
> 
> typedef itk::FFTComplexConjugateToRealImageFilter<pixelTypeC, dim2D> 
> IFFTFilterType;
> 
> typedef FFTFilterType::OutputImageType ComplexImageType;
> 
> typedef itk::MultiplyImageFilter<ComplexImageType, ComplexImageType, 
> ComplexImageType>MultiplyImageFilterType;//> 
> 
>  
> 
> constPadImage->SetPadLowerBound(paddin);// specifying padding options
> 
> constPadImage->SetPadUpperBound(paddin); 
> 
> constPadImage->SetInput(inputImage_C); // set padding filter input.
> 
> fftFilter->SetInput(constPadImage->GetOutput()); //set the fft.
> 
> ComplexImageType::Pointer fft_input = fftFilter->GetOutput(); // fft 
> filter done on image.
> 
> fftFilter->Update();
> 
>  
> 
> constPadImage2->SetPadUpperBound(paddin_wt_upper);   
> 
> constPadImage2->SetInput(inputImage2); // set padding filter input.
> 
> fft_wtFilter->SetInput(constPadImage2->GetOutput()); //set the fft.
> 
> ComplexImageType::Pointer fft_weight= fft_wtFilter->GetOutput();// fft 
> filter done on image.
> 
> fft_wtFilter->Update();
> 
>  
> 
> MultiplyImageFilter->SetInput1(fft_input);
> 
> MultiplyImageFilter->SetInput2(fft_weight);
> 
> MultiplyImageFilter->Update() // Error occurs here.
> 
> ifftFilter->SetInput(MultiplyImageFilter->GetOutput());
> 
> ifftFilter->Update();
> 
>  
> 
> Hi,Many thanks 
> 
> Saurabh
> 
> New ITKer..
> 
>  
> 
>  
> 
> 
> 
> 2008/11/21 chensiqi <pidanchen at hotmail.com <mailto:pidanchen at hotmail.com>>
> 
>      
>     Hi, ITKers,
>      
>     Does anybody know how to load sequence items using ITK? Such as "ROI
>     Contour Sequence".
>     Or if you know how to do it in GDCM, and integrate into ITK, that
>     will also be very helpful.
>      
>     Thanks
>     Siqi
> 
> 
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