[Insight-users] Bug in CastImageFIlter?

[Matthias Schabel]

Taking a quick look at the code, it appears that there is not a do- 
nothing specialization for
CastImageFilter in the case that the input and output image types are  
degenerate; this means
that a bunch of unnecessary work gets done if you call  
CastImageFilter<short,short>, for
example. Why, you ask, would you do something like that? Consider a  
generic class for
reading in DICOM data and, possibly converting it to another type via  
casting:

template<std::size_t R,typename T = short>
class DicomData :
	public itk::Image<T,R>
{
	public:
		DicomData(const std::vector<std::string>& filenames);
};

template<std::size_t R,typename T>
DicomData<R,T>::DicomData(const std::vector<std::string>& filenames)
{
	// use ImageSeriesReader to read DICOM data

	itk::Image<short,R>::Pointer	input_image_ptr = reader->GetOutput();

	typedef itk::CastImageFilter<itk::Image<short,R>,itk::Image<T,R> >	 
cast_image_filter_type;
	typedef typename cast_image_filter_type::Pointer				 
cast_image_filter_pointer_type;
	
	cast_image_filter_pointer_type	caster = cast_image_filter_type::New();

	caster->SetInput(input_image_ptr);
	
	try
	{
		// if T == short, this should do nothing, but it doesn't (do nothing)
		caster->Update();
	}
	catch (itk::ExceptionObject& e)
	{
		std::cerr << "exception in image series reader " << std::endl;
		std::cerr << e << std::endl;
		
		throw;
	}
	
	image_pointer_type::operator=(caster->GetOutput());
}

Really, all that is needed is a template specialization in  
CastImageFilter like this:

template<class TImage>
class CastImageFilter<TImage,TImage>
{
	// don't do anything, just return the input pointer...
}

Is there some reason why this isn't done? Maybe I'm missing some  
subtlety that precludes this...

Matthias
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