[Insight-developers] ITK v4: Why is NeighborhoodOperatorImageType restricted to signed types?

[Jim Miller]

I would guess it is because the filter was used to compute derivatives.

The exception is probably too restrictive. I am not sure that we can devise
a suitable test. Whether the output pixel type is signed is a function of
the sign of the elements of the kernel and the sign of the pixels in the
image. The inner product can take on different signs as a function of the
signs and magnitude of the elements of the kernel and the pixels in the
image.



On Fri, Jun 10, 2011 at 3:26 PM, Bill Lorensen <bill.lorensen at gmail.com>wrote:

> 2004 is a long time ago. I can't recall. I'll have to look at the code.
>
> Also I cc'ed the list in case someone else remembers.
>
> Bill
>
> On Fri, Jun 10, 2011 at 3:21 PM, Cory Quammen <cquammen at cs.unc.edu> wrote:
> > Hi Bill,
> >
> > I'm working with the NeighborhoodOperatorImageType and ran into a
> > problem with a exception that is thrown if the output pixel type is
> > not signed. Can you recall why you added that exception?
> >
> > A specific use case for allowing this filter to operate on unsigned
> > types would be the convolution of an unsigned char image with an
> > unsigned char kernel.
> >
> > Thanks,
> > Cory
> >
> > patronum:include cquammen$ git show
> ca27839eaa8a6f39326142d9de1302c1430e70b5
> > commit ca27839eaa8a6f39326142d9de1302c1430e70b5
> > Author: Bill Lorensen <bill.lorensen at gmail.com>
> > Date:   Sat Jun 5 08:27:00 2004 -0400
> >
> >    ENH: throw an exception if output pixel type is not signed.
> >
> > diff --git a/Code/BasicFilters/itkNeighborhoodOperatorImageFilter.txx
> > b/Code/BasicFilters/itkNeighborhoodOperatorImageFilter.txx
> > index 6573c1c..9ac807e 100644
> > --- a/Code/BasicFilters/itkNeighborhoodOperatorImageFilter.txx
> > +++ b/Code/BasicFilters/itkNeighborhoodOperatorImageFilter.txx
> > @@ -93,6 +93,11 @@ NeighborhoodOperatorImageFilter<TInputImage,
> TOutputImage>
> >   BFC faceCalculator;
> >   FaceListType faceList;
> >
> > +  // This filter can only operate on data types that are signed.
> > +  if (!NumericTraits<OutputPixelType>::is_signed)
> > +    {
> > +    itkExceptionMacro( << "This filter can only create images of
> > signed data type.");
> > +    }
> >   // Allocate output
> >   OutputImageType *output = this->GetOutput();
> >
> >
> >
> > --
> > Cory Quammen
> > Computer Integrated Systems for Microscopy and Manipulation (CISMM)
> > Department of Computer Science
> > University of North Carolina at Chapel Hill
> > http://www.cs.unc.edu/~cquammen
> >
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