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List:       vtkusers
Subject:    [vtkusers] Bug in the 3D version of vtkImageFFT or vtkImageRFFT ?
From:       "Cotin, Stephane M" <SCOTIN () PARTNERS ! ORG>
Date:       2000-08-29 21:36:18
Message-ID: 9E50C8A46320D311B4DC0008C7F4E296024B97F7 () phsexch5 ! mgh ! harvard ! edu
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Hi,

I'd like to report a strange behavior I observed today while trying to use the
3D version of vtkImageFFT and vtkImageRFFT.
I assumed (and I may be wrong here?) that the 3D inverse Fourier transform of
the 3D Fourier transform of a 3D image was the same as the original image. As a
matter of fact, this works perfectly well in 2D, as shown by the example:
TestRFFT.tcl
However, after changing "SetDimensionality 2" into "SetDimensionality 3" I got
very strange results: either a black image, or a noisy image.
I can't explain this behavior but it doesn't seem right...

Any idea?

Thanks,

-Stephane

PS: here is the script I used...

catch {load vtktcl}
if { [catch {set VTK_TCL $env(VTK_TCL)}] != 0} { set VTK_TCL "../../examplesTcl"
}
if { [catch {set VTK_DATA $env(VTK_DATA)}] != 0} { set VTK_DATA
"../../../vtkdata" }

# This scripts the reverse FFT. Pipeline is Reader->FFT->RFFT->Viewer.
# Output should be the same as Reader.


source vtkImageInclude.tcl

# Image pipeline

vtkImageReader reader
reader SetDataByteOrderToLittleEndian
reader SetDataExtent 0 255 0 255 1 93
reader SetFilePrefix "$VTK_DATA/fullHead/headsq"
reader SetDataMask 0x7fff
#reader DebugOn

vtkImageFFT fft
fft SetDimensionality 3
fft SetInput [reader GetOutput]
#fft DebugOn

vtkImageRFFT rfft
rfft SetDimensionality 3
rfft SetInput [fft GetOutput]
rfft ReleaseDataFlagOff
#fft DebugOn


vtkImageViewer viewer
viewer SetInput [rfft GetOutput]
viewer SetZSlice 22
viewer SetColorWindow 2000
viewer SetColorLevel 1000
#viewer DebugOn


# make interface
source WindowLevelInterface.tcl


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