<html><head><meta http-equiv="Content-Type" content="text/html charset=iso-8859-1"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hello,<br><div><br></div><div>Looking at the code:</div><div><br></div><div><a href="https://github.com/Kitware/ITK/blob/master/Modules/Filtering/FFT/include/itkFFTWForwardFFTImageFilter.hxx#L90">https://github.com/Kitware/ITK/blob/master/Modules/Filtering/FFT/include/itkFFTWForwardFFTImageFilter.hxx#L90</a></div><div><br></div><div>It looks like the output image is manually created internally, and the meta data is just not copied.</div><div><br></div><div>It should be a straight forward fix. And the other FFTW filters should be reviewed for a similar bug.</div><div><br></div><div>Cartik, are you volunteering to take care of this particular issue? Or are you talking about another issue?</div><div><br></div><div>Thanks,</div><div>Brad</div><div><br></div><div><div>On Sep 27, 2012, at 10:21 AM, Cartik Sharma <<a href="mailto:cartik.sharma@gmail.com">cartik.sharma@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">In addition to previous post and compiler statements from your message, we might need to introduce<br>filters to "cleanse" the data, reduce noise and then perform the actual FFTw transform. <br><br>This in combination with computing for the coefficients with <i><b>standard</b></i> FFT techniques should help<br>
remove the bug. As mentioned earlier, we also need to check for precision in computing coefficient<br>values.<br><br>-Cartik<br><br><div class="gmail_quote">On Thu, Sep 27, 2012 at 10:15 AM, Cartik Sharma <span dir="ltr"><<a href="mailto:cartik.sharma@gmail.com" target="_blank">cartik.sharma@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dear Kent, <br><br>From previous knowledge of Fourier transforms, this seems like it might have to do with computing<br>
coefficients with extreme precision. <br>Depending on the nature of data, there might also be the added problem with dimensionality reduction, so you might have to have a dimensionality reduction technique to filter out correlations in data components.<br>
<br>Please post the code and we'll correct the pos/space and orientation computation based on above suggestions and then have domain transformation with FFT as well as with reverse transformations<br>with the iFFTs.<br>
<br>Best regards,<br>Cartik <br><div class="HOEnZb"><div class="h5"><br><div class="gmail_quote">On Thu, Sep 27, 2012 at 10:00 AM, Williams, Norman K <span dir="ltr"><<a href="mailto:norman-k-williams@uiowa.edu" target="_blank">norman-k-williams@uiowa.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">This is code I wrote years ago, so I'd have stop what I'm doing and spend<br>
a couple hours reading the code to know what was really going on. But it<br>
sounds like the pos/orientation/spacing isn't being propogated from the<br>
input to the FFT and by the IFFT to the output.<br>
<br>
I would argue that this should always happen -- an image converted to the<br>
frequency domain doesn't transform it spatially; no matter what you do in<br>
the frequency domain, when you transform back to the spatial domain, it<br>
should be oriented and positioned the same.<br>
<br>
--<br>
Kent Williams <a href="mailto:norman-k-williams@uiowa.edu" target="_blank">norman-k-williams@uiowa.edu</a><br>
<div><br>
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<br>
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<br>
On 9/27/12 7:13 AM, "Bradley Lowekamp" <<a href="mailto:blowekamp@mail.nih.gov" target="_blank">blowekamp@mail.nih.gov</a>> wrote:<br>
<br>
>Hello,<br>
><br>
>I have compiled SimpleITK with FFTW and I am getting the following<br>
>regression test failue:<br>
><br>
>81: [ RUN ] BasicFilters.ForwardFFT_defaults<br>
>81: Starting image compare on BasicFilters_ForwardFFT_defaults_<br>
>81: Loading baseline<br>
>/Users/blowekamp/src/SimpleITK/Testing/Data/Baseline/BasicFilters_ForwardF<br>
>FT_defaults.nrrd<br>
>81:<br>
>/scratch/blowekamp/build/SimpleITK/SimpleITK-build/Testing/Unit/sitkForwar<br>
>dFFTImageFilterTest.cxx:128: Failure<br>
>81: Value of: imageCompare.compare( output, "", "" )<br>
>81: Actual: false<br>
>81: Expected: true<br>
>81: ImageCompare: Failed to subtract image<br>
>/Users/blowekamp/src/SimpleITK/Testing/Data/Baseline/BasicFilters_ForwardF<br>
>FT_defaults.nrrd because:<br>
>/scratch/blowekamp/build/SimpleITK/ITK-prefix/include/ITK-4.2/itkImageToIm<br>
>ageFilter.hxx:243:<br>
>81: itk::ERROR: SubtractImageFilter(0x7ffe943009e0): Inputs do not occupy<br>
>the same physical space!<br>
>81: InputImage Origin: [0.0000000e+00, 0.0000000e+00, 0.0000000e+00],<br>
>InputImageIndexedDataObject1 Origin: [2.8345293e-01, 2.8345293e-01,<br>
>2.8345293e-01]<br>
>81: Tolerance: 1.0000000e-06<br>
>81: InputImage Spacing: [1.0000000e+00, 1.0000000e+00, 1.0000000e+00],<br>
>InputImageIndexedDataObject1 Spacing: [7.5587445e-01, 7.5587445e-01,<br>
>7.5587445e-01]<br>
>81: Tolerance: 1.0000000e-06<br>
><br>
><br>
>This is telling me that the vnl and the FFTW implementation of the<br>
>ForwardFFT image filter are handling the spacing different. The second<br>
>input is the baseline originating from the Vnl FFT implementation, while<br>
>the one from FFTW still has the default origin and spacing. However, I am<br>
>uncertain that this actually make sense, as the FFTForward filter does<br>
>converts from the spacial domain to the frequency this physical<br>
>information may not be very logical.<br>
><br>
>What should the correct behavior be?<br>
><br>
>Thanks,<br>
>Brad<br>
><br>
>ps<br>
>Please note that this exception is coming from the cumbersome standard<br>
>check in the ImageToImageFilter during comparison to the baseline. And<br>
>it's revealing a true bug.<br>
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