[Insight-users] CastImageFilter BUG???

[Lars Friedrich Lars]

Hello,

as can be retrieved from itk::CastImageFilter's Doxygen-entry, this filter can obviously be used for casting a 3D-volume to a 2D-slice (dimension-reduction).

"... If you attempt to cast an image to a lower dimension, the first "slice" (or line or volume) will be extracted. ..."

I've been using this functionality for a while in an application. However, today I changed something in the code (at completely different code-fragment) and from this point my application started to throw segfaults when executing it.
I traced the bug (in current ITK-CVS-version) and found out that casting from a 3D-slice to a 2D-image causes the segfault. Inspecting the code of itk::CastImageFilter and its superclass itk::UnaryFunctorImageFilter showed me that the code lines 97-112 of itkUnaryFunctorImageFilter.txx seem to cause the segfault:

  for (i=0; i < Superclass::InputImageDimension; ++i)
      {
      outputSpacing[i] = inputSpacing[i];
      outputOrigin[i] = inputOrigin[i];
      for (j=0; j < Superclass::OutputImageDimension; j++)
        {
        if (j < Superclass::InputImageDimension)
          {
          outputDirection[j][i] = inputDirection[j][i];
          }
        else
          {
          outputDirection[j][i] = 0.0;
          }
        }
      }

When casting from 3D to 2D the InputImageDimension=3, but the OutputImageDimension=2. Writing to the 3rd elements of outputSpacing, outputOrigin and outputDirection causes the memory-violation.

Please correct me if I am wrong.

However, it is scary and funny at the same time that my application has worked without throwing segfaults and without any obvious errors for a few weeks ...

The example program below shows the bug (if it is a bug).

regards,

lars


// TestReductionCasting.cxx

#include <iostream>
#include <stdlib.h>
#include <time.h>

#include <itkCastImageFilter.h>
#include <itkImage.h>
#include <itkImageRegionIterator.h>

int main(int argc, char *argv[])
{
  std::cerr << "Constructing 3D image ...";
  typedef itk::Image<float, 3> Image3DType;
  typedef itk::ImageRegionIterator<Image3DType> IteratorType;

  Image3DType::RegionType region;
  Image3DType::SizeType size;
  Image3DType::IndexType start;
  Image3DType::SpacingType spacing;
  Image3DType::PointType origin;
  Image3DType::DirectionType orientation;

  size[0] = 100; size[1] = 200; size[2] = 1;
  start.Fill(0);
  region.SetIndex(start);
  region.SetSize(size);
  spacing[0] = 0.25; spacing[1] = 0.5; spacing[2] = 1;
  origin[0] = 100; origin[1] = 200; origin[2] = -50;
  orientation.SetIdentity();
  Image3DType::Pointer image = Image3DType::New();
  image->SetRegions(region);
  image->SetSpacing(spacing);
  image->SetOrigin(origin);
  image->SetDirection(orientation);
  image->Allocate();

  srand(time(NULL));
  IteratorType it(image, region);
  for (it.GoToBegin(); !it.IsAtEnd(); ++it)
  {
    it.Set(static_cast<float>(rand() % 100));
  }
  std::cerr << " DONE\n";

  std::cerr << "Casting to 2D image (cast image filter) ...";
  typedef itk::Image<unsigned char, 2> Image2DType;
  typedef itk::CastImageFilter<Image3DType, Image2DType> CasterType;

  CasterType::Pointer caster = CasterType::New();
  caster->SetInput(image);
  try
  {
    caster->Update(); // CAUSES SEGFAULT!!!
    std::cerr << " DONE\n";
  }
  catch (itk::ExceptionObject &e)
  {
    std::cerr << " ERROR\n";
  }

  return EXIT_SUCCESS;
}

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