[vtkusers] Is there a bug in vtkImageFFT?

[Bernard Chiu]

Hi,

I am trying to understand how vtkImageFFT works before using a similar
method to process my image. I found that there is a run-time error. I wrote
the following:

-----------------------------------------------------------------------------------------------------------
vtkXMLImageDataReader* vtkxmlreader = vtkXMLImageDataReader::New();
vtkxmlreader->SetFileName((LPCSTR) inputfile);

vtkImageFFT* fft = vtkImageFFT::New();
fft->SetInputConnection(vtkxmlreader->GetOutputPort());

vtkXMLImageDataWriter* vtkxmlwriter = vtkXMLImageDataWriter::New();
vtkxmlwriter->SetInputConnection(fft->GetOutputPort());
vtkxmlwriter->SetFileName("C:\\testfft.vti");
vtkxmlwriter->Write();

vtkxmlreader->Delete();
fft->Delete();
vtkxmlwriter->Delete();
--------------------------------------------------------------------------------------------------------------

I understand why the error occurred, but didn't know what is the best
approach to make it work. I found that in the vtkImageFFT::ThreadedExecute
method, there is a line

outPtr = outData->GetScalarPointerForExtent(outExt);

This statement always return NULL, because vtkImageData::GetArrayPointer has
an if-statement that does the following:

  if (idx < 0 || idx > array->GetMaxId())
    {
    vtkErrorMacro("Coordinate (" << coordinate[0] << ", " << coordinate[1]
                  << ", " << coordinate[2] << ") out side of array (max = "
                  << array->GetMaxId());
    return NULL;
    }

Since the scalar array of the output image has not been initialized, MaxId
is always -1 and NULL is always returned.

Run-time error therefore must occur at vtkImageFFT::vtkImageFFTExecute.

Could anyone tell me whether there is anything a user can do? I don't want
to change the vtk code.

Thanks,
Bernard
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