[Insight-users] bug in gradientRecursiveGaussianImageFilter?

[Martin Urschler]

hello,

i was digging into the GradientRecursiveGaussian filter and found 
something that might cause seg faults (actually i wonder why it doesn´t)

I use 3D images, i.e. ImageDimension equals 3

The class creates 2 smoothing Image filters and one derivative filter 
in my case. In the generateData method of this filter there is a while 
loop setting up the directions of these 3 filters.

for (unsigned int dim=0; dim < ImageDimension; ++dim)
{
   unsigned int i=0;
   unsigned int j=0;
   while( i < ImageDimension )
   {
      if (i == dim)
      {
         j++;
      }

      std::cout << "setting smoothing filter[" i <<         "] to 
direction [" << j << "]" << std::endl;

      m_SmoothingFilters[i]->SetDirection( j );
      ++i;
      ++j;
   }

   m_DerivativeFilter->SetDirection( dim );

   .... do the other stuff ....
}

If I introduce the cout message as shown above I get the following 
console output:

dim = 0:
setting smoothing filter [0] to direction [1]
setting smoothing filter [1] to direction [2]
setting smoothing filter [2] to direction [3]

dim = 1:
setting smoothing filter [0] to direction [0]
setting smoothing filter [1] to direction [2]
setting smoothing filter [2] to direction [3]

dim = 2:
setting smoothing filter [0] to direction [0]
setting smoothing filter [1] to direction [1]
setting smoothing filter [2] to direction [3]


However smoothing filter [2] has nowhere been created. I guess this 
should segfault, at least sometimes, but obviously it doesn't which is 
strange since every registration application using a metric derived 
from itkImageToImageMetric uses this class to calculate moving image 
derivatives. so there should be lots of test cases all around the 
world...

regards, Martin