[Insight-developers] ImageIterators : Suggested Patch: Exception

[Bradley Lowekamp]

I ran into this issue with trying to improve the ShrinkImageFilter. I  
think this is a good check to make. In my case we only had test  
failing on one or two systems, even through the buffer was being  
accessed outside the buffered region.

However, this seems like an assertion of preconditions. In this case  
the precondition is that the region parameter must be with in the  
buffered region. There are a variety of ways to verify preconditions.  
One way is to use an assert type macro that is only implemented in  
Debug versions. Do we have any guidelines for asserts or verification  
of preconditions in ITK?

Brad


On May 5, 2009, at 11:07 AM, Luis Ibanez wrote:

> With Michel Audette we have been tracking the issues related to
> aligning physical point coordinates with index coordinates.
>
> In the process we noticed that the ITK image iterators do not
> verify at construction time whether the region given as argument
> to the iterator constructor,  is inside of the image or not.
>
> The consequence is that a user can provide a region outside
> of the image, we compute the offset (that will turn out to be
> outside of the image buffer) and then we (incorrectly) provide
> access to the pixel location.
>
> This has now been reported as Bug #8960:
>
>     http://public.kitware.com/Bug/view.php?id=8960
>
>
> We are suggesting the following fix to this problem:
>
> Namely, to check the region argument of the iterator constructor
> against the BufferedRegion of the image, and throw an exception
> if the region is not fully inside of the image buffered region.
>
>
> Index: itkImageConstIterator.h
> ===================================================================
> RCS file: /cvsroot/Insight/Insight/Code/Common/ 
> itkImageConstIterator.h,v
> retrieving revision 1.23
> diff -r1.23 itkImageConstIterator.h
> 175a176,183
>>    const RegionType & bufferedRegion = m_Image->GetBufferedRegion();
>>
>>    if( ! bufferedRegion.IsInside( m_Region ) )
>>      {
>>      itkGenericExceptionMacro("Region " << m_Region
>>        << " is outside of buffered region " << bufferedRegion );
>>      }
>>
> Index: itkImageConstIteratorWithIndex.txx
> ===================================================================
> RCS file: /cvsroot/Insight/Insight/Code/Common/ 
> itkImageConstIteratorWithIndex.txx,v
> retrieving revision 1.27
> diff -r1.27 itkImageConstIteratorWithIndex.txx
> 84a85,92
>>  const RegionType & bufferedRegion = m_Image->GetBufferedRegion();
>>
>>  if( ! bufferedRegion.IsInside( m_Region ) )
>>    {
>>    itkGenericExceptionMacro("Region " << m_Region
>>      << " is outside of buffered region " << bufferedRegion );
>>    }
>>
>
>
> Does anyone see a problem with this patch ?
>
> Any objections ?
>
>
>   Thanks
>
>
>        Luis
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========================================================
Bradley Lowekamp
Lockheed Martin Contractor for
Office of High Performance Computing and Communications
National Library of Medicine
blowekamp at mail.nih.gov

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