#include <itkHessian3DToVesselnessMeasureImageFilter.h>

Inheritance diagram for itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >:

Collaboration diagram for itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >:

Public Types
using	ConstPointer = SmartPointer< const Self >

using	EigenAnalysisFilterType = SymmetricEigenAnalysisFixedDimensionImageFilter< ImageDimension, InputImageType, EigenValueImageType >

using	EigenValueArrayType = FixedArray< double, Self::InputPixelDimension >

using	EigenValueImageType = Image< EigenValueArrayType, Self::ImageDimension >

using	InputImageType = typename Superclass::InputImageType

using	InputPixelType = typename InputImageType::PixelType

using	OutputImageType = typename Superclass::OutputImageType

using	OutputPixelType = TPixel

using	Pointer = SmartPointer< Self >

using	Self = Hessian3DToVesselnessMeasureImageFilter

using	Superclass = ImageToImageFilter< Image< SymmetricSecondRankTensor< double, 3 >, 3 >, Image< TPixel, 3 > >

Public Types inherited from itk::ImageToImageFilter< Image< SymmetricSecondRankTensor< double, 3 >, 3 >, Image< TPixel, 3 > >
using	ConstPointer = SmartPointer< const Self >

using	InputImageConstPointer = typename InputImageType::ConstPointer

using	InputImagePixelType = typename InputImageType::PixelType

using	InputImagePointer = typename InputImageType::Pointer

using	InputImageRegionType = typename InputImageType::RegionType

using	InputImageType = Image< SymmetricSecondRankTensor< double, 3 >, 3 >

using	OutputImagePixelType = typename Superclass::OutputImagePixelType

using	OutputImageRegionType = typename Superclass::OutputImageRegionType

using	Pointer = SmartPointer< Self >

using	Self = ImageToImageFilter

using	Superclass = ImageSource< Image< TPixel, 3 > >

Public Types inherited from itk::ImageSource< Image< TPixel, 3 > >
using	ConstPointer = SmartPointer< const Self >

using	DataObjectIdentifierType = Superclass::DataObjectIdentifierType

using	DataObjectPointer = DataObject::Pointer

using	DataObjectPointerArraySizeType = Superclass::DataObjectPointerArraySizeType

using	OutputImagePixelType = typename OutputImageType::PixelType

using	OutputImagePointer = typename OutputImageType::Pointer

using	OutputImageRegionType = typename OutputImageType::RegionType

using	OutputImageType = Image< TPixel, 3 >

using	Pointer = SmartPointer< Self >

using	Self = ImageSource

using	Superclass = ProcessObject

Public Types inherited from itk::ProcessObject
using	ConstPointer = SmartPointer< const Self >

using	DataObjectIdentifierType = DataObject::DataObjectIdentifierType

using	DataObjectPointer = DataObject::Pointer

using	DataObjectPointerArray = std::vector< DataObjectPointer >

using	DataObjectPointerArraySizeType = DataObjectPointerArray::size_type

using	MultiThreaderType = MultiThreaderBase

using	NameArray = std::vector< DataObjectIdentifierType >

using	Pointer = SmartPointer< Self >

using	Self = ProcessObject

using	Superclass = Object

Public Types inherited from itk::Object
using	ConstPointer = SmartPointer< const Self >

using	Pointer = SmartPointer< Self >

using	Self = Object

using	Superclass = LightObject

Public Types inherited from itk::LightObject
using	ConstPointer = SmartPointer< const Self >

using	Pointer = SmartPointer< Self >

using	Self = LightObject

Public Member Functions
virtual ::itk::LightObject::Pointer	CreateAnother () const

virtual const char *	GetNameOfClass () const

Public Member Functions inherited from itk::ImageToImageFilter< Image< SymmetricSecondRankTensor< double, 3 >, 3 >, Image< TPixel, 3 > >
const InputImageType *	GetInput () const

const InputImageType *	GetInput (unsigned int idx) const

void	PopBackInput () override

void	PopFrontInput () override

virtual void	PushBackInput (const InputImageType *input)

virtual void	PushFrontInput (const InputImageType *input)

virtual void	SetInput (const DataObjectIdentifierType &key, DataObject *input)

virtual void	SetInput (const InputImageType *input)

virtual void	SetInput (unsigned int, const Image< SymmetricSecondRankTensor< double, 3 >, 3 > *image)

virtual void	SetCoordinateTolerance (double _arg)

virtual double	GetCoordinateTolerance () const

virtual void	SetDirectionTolerance (double _arg)

virtual double	GetDirectionTolerance () const

Public Member Functions inherited from itk::ImageSource< Image< TPixel, 3 > >
OutputImageType *	GetOutput ()

const OutputImageType *	GetOutput () const

OutputImageType *	GetOutput (unsigned int idx)

virtual void	GraftOutput (DataObject *graft)

virtual void	GraftOutput (const DataObjectIdentifierType &key, DataObject *graft)

virtual void	GraftNthOutput (unsigned int idx, DataObject *graft)

ProcessObject::DataObjectPointer	MakeOutput (ProcessObject::DataObjectPointerArraySizeType idx) override

ProcessObject::DataObjectPointer	MakeOutput (const ProcessObject::DataObjectIdentifierType &) override

Public Member Functions inherited from itk::ProcessObject
virtual void	AbortGenerateDataOff ()

virtual void	AbortGenerateDataOn ()

virtual void	EnlargeOutputRequestedRegion (DataObject *)

virtual const bool &	GetAbortGenerateData () const

DataObjectPointerArray	GetIndexedInputs ()

DataObjectPointerArray	GetIndexedOutputs ()

NameArray	GetInputNames () const

DataObjectPointerArray	GetInputs ()

DataObjectPointerArraySizeType	GetNumberOfIndexedInputs () const

DataObjectPointerArraySizeType	GetNumberOfIndexedOutputs () const

DataObjectPointerArraySizeType	GetNumberOfInputs () const

DataObjectPointerArraySizeType	GetNumberOfOutputs () const

virtual DataObjectPointerArraySizeType	GetNumberOfValidRequiredInputs () const

NameArray	GetOutputNames () const

DataObjectPointerArray	GetOutputs ()

virtual float	GetProgress () const

NameArray	GetRequiredInputNames () const

bool	HasInput (const DataObjectIdentifierType &key) const

bool	HasOutput (const DataObjectIdentifierType &key) const

void	IncrementProgress (float increment)

virtual void	PropagateRequestedRegion (DataObject *output)

virtual void	ResetPipeline ()

virtual void	SetAbortGenerateData (bool _arg)

virtual void	Update ()

virtual void	UpdateLargestPossibleRegion ()

virtual void	UpdateOutputData (DataObject *output)

virtual void	UpdateOutputInformation ()

void	UpdateProgress (float progress)

virtual void	SetReleaseDataFlag (bool val)

virtual bool	GetReleaseDataFlag () const

void	ReleaseDataFlagOn ()

void	ReleaseDataFlagOff ()

virtual void	SetReleaseDataBeforeUpdateFlag (bool _arg)

virtual const bool &	GetReleaseDataBeforeUpdateFlag () const

virtual void	ReleaseDataBeforeUpdateFlagOn ()

virtual void	ReleaseDataBeforeUpdateFlagOff ()

virtual void	SetNumberOfWorkUnits (ThreadIdType _arg)

virtual const ThreadIdType &	GetNumberOfWorkUnits () const

MultiThreaderType *	GetMultiThreader () const

void	SetMultiThreader (MultiThreaderType *threader)

virtual void	PrepareOutputs ()

Public Member Functions inherited from itk::Object
unsigned long	AddObserver (const EventObject &event, Command *)

unsigned long	AddObserver (const EventObject &event, Command *) const

unsigned long	AddObserver (const EventObject &event, std::function< void(const EventObject &)> function) const

virtual void	DebugOff () const

virtual void	DebugOn () const

Command *	GetCommand (unsigned long tag)

bool	GetDebug () const

MetaDataDictionary &	GetMetaDataDictionary ()

const MetaDataDictionary &	GetMetaDataDictionary () const

virtual ModifiedTimeType	GetMTime () const

virtual const TimeStamp &	GetTimeStamp () const

bool	HasObserver (const EventObject &event) const

void	InvokeEvent (const EventObject &)

void	InvokeEvent (const EventObject &) const

virtual void	Modified () const

void	Register () const override

void	RemoveAllObservers ()

void	RemoveObserver (unsigned long tag)

void	SetDebug (bool debugFlag) const

void	SetReferenceCount (int) override

void	UnRegister () const noexcept override

void	SetMetaDataDictionary (const MetaDataDictionary &rhs)

void	SetMetaDataDictionary (MetaDataDictionary &&rrhs)

virtual void	SetObjectName (std::string _arg)

virtual const std::string &	GetObjectName () const

Public Member Functions inherited from itk::LightObject
Pointer	Clone () const

virtual void	Delete ()

virtual int	GetReferenceCount () const

void	Print (std::ostream &os, Indent indent=0) const

Static Public Member Functions
static Pointer	New ()

Static Public Member Functions inherited from itk::ImageToImageFilter< Image< SymmetricSecondRankTensor< double, 3 >, 3 >, Image< TPixel, 3 > >
static void	SetGlobalDefaultDirectionTolerance (double)

static double	GetGlobalDefaultDirectionTolerance ()

static void	SetGlobalDefaultCoordinateTolerance (double)

static double	GetGlobalDefaultCoordinateTolerance ()

Static Public Member Functions inherited from itk::Object
static bool	GetGlobalWarningDisplay ()

static void	GlobalWarningDisplayOff ()

static void	GlobalWarningDisplayOn ()

static Pointer	New ()

static void	SetGlobalWarningDisplay (bool val)

Static Public Member Functions inherited from itk::LightObject
static void	BreakOnError ()

static Pointer	New ()

Static Public Attributes
static constexpr unsigned int	ImageDimension = InputImageType::ImageDimension

static constexpr unsigned int	InputPixelDimension = InputPixelType::Dimension

Static Public Attributes inherited from itk::ImageToImageFilter< Image< SymmetricSecondRankTensor< double, 3 >, 3 >, Image< TPixel, 3 > >
static constexpr unsigned int	InputImageDimension

static constexpr unsigned int	OutputImageDimension

Static Public Attributes inherited from itk::ImageSource< Image< TPixel, 3 > >
static constexpr unsigned int	OutputImageDimension

EigenAnalysisFilterType::Pointer	m_SymmetricEigenValueFilter

double	m_Alpha1

double	m_Alpha2

virtual void	SetAlpha1 (double _arg)

virtual double	GetAlpha1 () const

virtual void	SetAlpha2 (double _arg)

virtual double	GetAlpha2 () const

	Hessian3DToVesselnessMeasureImageFilter ()

	~Hessian3DToVesselnessMeasureImageFilter () override=default

void	PrintSelf (std::ostream &os, Indent indent) const override

void	GenerateData () override

Additional Inherited Members
Protected Types inherited from itk::ImageToImageFilter< Image< SymmetricSecondRankTensor< double, 3 >, 3 >, Image< TPixel, 3 > >
using	InputToOutputRegionCopierType = ImageToImageFilterDetail::ImageRegionCopier< Self::OutputImageDimension, Self::InputImageDimension >

using	OutputToInputRegionCopierType = ImageToImageFilterDetail::ImageRegionCopier< Self::InputImageDimension, Self::OutputImageDimension >

Protected Member Functions inherited from itk::ImageToImageFilter< Image< SymmetricSecondRankTensor< double, 3 >, 3 >, Image< TPixel, 3 > >
void	PushBackInput (const DataObject *input) override

void	PushFrontInput (const DataObject *input) override

	ImageToImageFilter ()

	~ImageToImageFilter () override=default

void	PrintSelf (std::ostream &os, Indent indent) const override

void	VerifyInputInformation () ITKv5_CONST override

void	GenerateInputRequestedRegion () override

virtual void	CallCopyOutputRegionToInputRegion (InputImageRegionType &destRegion, const OutputImageRegionType &srcRegion)

virtual void	CallCopyInputRegionToOutputRegion (OutputImageRegionType &destRegion, const InputImageRegionType &srcRegion)

Protected Member Functions inherited from itk::ImageSource< Image< TPixel, 3 > >
	ImageSource ()

	~ImageSource () override=default

void	GenerateData () override

void	ClassicMultiThread (ThreadFunctionType callbackFunction)

virtual void	ThreadedGenerateData (const OutputImageRegionType &region, ThreadIdType threadId)

virtual void	DynamicThreadedGenerateData (const OutputImageRegionType &outputRegionForThread)

virtual void	AllocateOutputs ()

virtual void	BeforeThreadedGenerateData ()

virtual void	AfterThreadedGenerateData ()

virtual const ImageRegionSplitterBase *	GetImageRegionSplitter () const

virtual unsigned int	SplitRequestedRegion (unsigned int i, unsigned int pieces, OutputImageRegionType &splitRegion)

virtual bool	GetDynamicMultiThreading () const

virtual void	SetDynamicMultiThreading (bool _arg)

virtual void	DynamicMultiThreadingOn ()

virtual void	DynamicMultiThreadingOff ()

Protected Member Functions inherited from itk::ProcessObject
	ProcessObject ()

	~ProcessObject () override

DataObject *	GetInput (const DataObjectIdentifierType &key)

const DataObject *	GetInput (const DataObjectIdentifierType &key) const

DataObject *	GetInput (DataObjectPointerArraySizeType idx)

const DataObject *	GetInput (DataObjectPointerArraySizeType idx) const

virtual void	SetInput (const DataObjectIdentifierType &key, DataObject *input)

virtual void	SetNthInput (DataObjectPointerArraySizeType idx, DataObject *input)

virtual void	AddInput (DataObject *input)

virtual void	RemoveInput (const DataObjectIdentifierType &key)

virtual void	RemoveInput (DataObjectPointerArraySizeType)

DataObject *	GetPrimaryInput ()

const DataObject *	GetPrimaryInput () const

virtual void	SetPrimaryInputName (const DataObjectIdentifierType &key)

virtual const char *	GetPrimaryInputName () const

virtual void	SetPrimaryInput (DataObject *object)

void	SetNumberOfIndexedInputs (DataObjectPointerArraySizeType num)

virtual void	SetNumberOfRequiredInputs (DataObjectPointerArraySizeType)

virtual const DataObjectPointerArraySizeType &	GetNumberOfRequiredInputs () const

bool	RemoveRequiredInputName (const DataObjectIdentifierType &)

bool	IsRequiredInputName (const DataObjectIdentifierType &) const

void	SetRequiredInputNames (const NameArray &)

bool	AddRequiredInputName (const DataObjectIdentifierType &)

bool	AddRequiredInputName (const DataObjectIdentifierType &, DataObjectPointerArraySizeType idx)

void	AddOptionalInputName (const DataObjectIdentifierType &)

void	AddOptionalInputName (const DataObjectIdentifierType &, DataObjectPointerArraySizeType idx)

DataObject *	GetOutput (const DataObjectIdentifierType &key)

const DataObject *	GetOutput (const DataObjectIdentifierType &key) const

virtual void	SetPrimaryOutputName (const DataObjectIdentifierType &key)

virtual const char *	GetPrimaryOutputName () const

DataObject *	GetOutput (DataObjectPointerArraySizeType i)

const DataObject *	GetOutput (DataObjectPointerArraySizeType i) const

virtual void	SetOutput (const DataObjectIdentifierType &name, DataObject *output)

virtual void	RemoveOutput (const DataObjectIdentifierType &key)

DataObject *	GetPrimaryOutput ()

const DataObject *	GetPrimaryOutput () const

virtual void	SetPrimaryOutput (DataObject *object)

virtual void	SetNthOutput (DataObjectPointerArraySizeType idx, DataObject *output)

virtual void	AddOutput (DataObject *output)

virtual void	RemoveOutput (DataObjectPointerArraySizeType idx)

virtual void	SetNumberOfRequiredOutputs (DataObjectPointerArraySizeType _arg)

virtual const DataObjectPointerArraySizeType &	GetNumberOfRequiredOutputs () const

void	SetNumberOfIndexedOutputs (DataObjectPointerArraySizeType num)

DataObjectIdentifierType	MakeNameFromInputIndex (DataObjectPointerArraySizeType idx) const

DataObjectIdentifierType	MakeNameFromOutputIndex (DataObjectPointerArraySizeType idx) const

DataObjectPointerArraySizeType	MakeIndexFromInputName (const DataObjectIdentifierType &name) const

DataObjectPointerArraySizeType	MakeIndexFromOutputName (const DataObjectIdentifierType &name) const

bool	IsIndexedInputName (const DataObjectIdentifierType &) const

bool	IsIndexedOutputName (const DataObjectIdentifierType &) const

virtual void	VerifyPreconditions () ITKv5_CONST

virtual void	GenerateOutputRequestedRegion (DataObject *output)

virtual void	GenerateOutputInformation ()

virtual void	PropagateResetPipeline ()

virtual void	ReleaseInputs ()

virtual void	CacheInputReleaseDataFlags ()

virtual void	RestoreInputReleaseDataFlags ()

virtual bool	GetThreaderUpdateProgress () const

virtual void	ThreaderUpdateProgressOn ()

virtual void	ThreaderUpdateProgressOff ()

virtual void	SetThreaderUpdateProgress (bool arg)

Protected Member Functions inherited from itk::Object
	Object ()

	~Object () override

bool	PrintObservers (std::ostream &os, Indent indent) const

virtual void	SetTimeStamp (const TimeStamp &timeStamp)

Protected Member Functions inherited from itk::LightObject
virtual LightObject::Pointer	InternalClone () const

	LightObject ()

virtual void	PrintHeader (std::ostream &os, Indent indent) const

virtual void	PrintTrailer (std::ostream &os, Indent indent) const

virtual	~LightObject ()

Static Protected Member Functions inherited from itk::ImageSource< Image< TPixel, 3 > >
static const ImageRegionSplitterBase *	GetGlobalDefaultSplitter ()

static ITK_THREAD_RETURN_FUNCTION_CALL_CONVENTION	ThreaderCallback (void *arg)

Static Protected Member Functions inherited from itk::ProcessObject
static constexpr float	progressFixedToFloat (uint32_t fixed)

static uint32_t	progressFloatToFixed (float f)

Protected Attributes inherited from itk::ImageSource< Image< TPixel, 3 > >
bool	m_DynamicMultiThreading

Protected Attributes inherited from itk::ProcessObject
bool	m_Updating

TimeStamp	m_OutputInformationMTime

Protected Attributes inherited from itk::LightObject
std::atomic< int >	m_ReferenceCount

Detailed Description

template<typename TPixel>
class itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >

Line filter to provide a vesselness measure for tubular objects from the hessian matrix.

The filter takes as input an image of hessian pixels (SymmetricSecondRankTensor pixels) and preserves pixels that have eigen values $\lambda_3$ close to 0 and $\lambda_2$ and $\lambda_1$ as large negative values (for bright tubular structures).

$| \lambda_1 | < | \lambda_2 | < | \lambda_3 |$

Notes:: The filter takes into account that the eigen values play a crucial role in discriminating shape and orientation of structures.

Bright tubular structures will have low $\lambda_1$ and large negative values of $\lambda_2$ and $\lambda_3$ .
Conversely dark tubular structures will have a low value of $\lambda_1$ and large positive values of $\lambda_2$ and $\lambda_3$ .
Bright plate like structures have low values of $\lambda_1$ and $\lambda_2$ and large negative values of $\lambda_3$
Dark plate like structures have low values of $\lambda_1$ and $\lambda_2$ and large positive values of $\lambda_3$
Bright spherical (blob) like structures have all three eigen values as large negative numbers
Dark spherical (blob) like structures have all three eigen values as large positive numbers

This filter is used to discriminate the Bright tubular structures.

References:: "3D Multi-scale line filter for segmentation and visualization of curvilinear structures in medical images", Yoshinobu Sato, Shin Nakajima, Hideki Atsumi, Thomas Koller, Guido Gerig, Shigeyuki Yoshida, Ron Kikinis.

http://www.image.med.osaka-u.ac.jp/member/yoshi/paper/linefilter.pdf

See also: HessianRecursiveGaussianImageFilter; SymmetricEigenAnalysisImageFilter; SymmetricSecondRankTensor

Examples: Examples/Filtering/VesselnessMeasureImageFilter.cxx, and SphinxExamples/src/Filtering/ImageFeature/SegmentBloodVessels/Code.cxx.

Definition at line 77 of file itkHessian3DToVesselnessMeasureImageFilter.h.

Member Typedef Documentation

◆ ConstPointer

template<typename TPixel >

using itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::ConstPointer = SmartPointer<const Self>

Definition at line 88 of file itkHessian3DToVesselnessMeasureImageFilter.h.

◆ EigenAnalysisFilterType

template<typename TPixel >

using itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::EigenAnalysisFilterType = SymmetricEigenAnalysisFixedDimensionImageFilter<ImageDimension, InputImageType, EigenValueImageType>

Definition at line 102 of file itkHessian3DToVesselnessMeasureImageFilter.h.

◆ EigenValueArrayType

template<typename TPixel >

using itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::EigenValueArrayType = FixedArray<double, Self::InputPixelDimension>

Definition at line 99 of file itkHessian3DToVesselnessMeasureImageFilter.h.

◆ EigenValueImageType

template<typename TPixel >

using itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::EigenValueImageType = Image<EigenValueArrayType, Self::ImageDimension>

Definition at line 100 of file itkHessian3DToVesselnessMeasureImageFilter.h.

◆ InputImageType

template<typename TPixel >

using itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::InputImageType = typename Superclass::InputImageType

Definition at line 90 of file itkHessian3DToVesselnessMeasureImageFilter.h.

◆ InputPixelType

template<typename TPixel >

using itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::InputPixelType = typename InputImageType::PixelType

Definition at line 92 of file itkHessian3DToVesselnessMeasureImageFilter.h.

◆ OutputImageType

template<typename TPixel >

using itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::OutputImageType = typename Superclass::OutputImageType

Definition at line 91 of file itkHessian3DToVesselnessMeasureImageFilter.h.

◆ OutputPixelType

template<typename TPixel >

using itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::OutputPixelType = TPixel

Definition at line 93 of file itkHessian3DToVesselnessMeasureImageFilter.h.

◆ Pointer

template<typename TPixel >

using itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::Pointer = SmartPointer<Self>

Definition at line 87 of file itkHessian3DToVesselnessMeasureImageFilter.h.

◆ Self

template<typename TPixel >

using itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::Self = Hessian3DToVesselnessMeasureImageFilter

Standard class type aliases.

Definition at line 84 of file itkHessian3DToVesselnessMeasureImageFilter.h.

◆ Superclass

template<typename TPixel >

using itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::Superclass = ImageToImageFilter<Image<SymmetricSecondRankTensor<double, 3>, 3>, Image<TPixel, 3> >

Definition at line 85 of file itkHessian3DToVesselnessMeasureImageFilter.h.

Constructor & Destructor Documentation

◆ Hessian3DToVesselnessMeasureImageFilter()

template<typename TPixel >

itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::Hessian3DToVesselnessMeasureImageFilter ( )

protected

Set/Get macros for alpha_1. Please refer to http://www.image.med.osaka-u.ac.jp/member/yoshi/paper/linefilter.pdf

◆ ~Hessian3DToVesselnessMeasureImageFilter()

template<typename TPixel >

itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::~Hessian3DToVesselnessMeasureImageFilter ( )

overrideprotecteddefault

Set/Get macros for alpha_1. Please refer to http://www.image.med.osaka-u.ac.jp/member/yoshi/paper/linefilter.pdf

Member Function Documentation

◆ CreateAnother()

template<typename TPixel >

virtual::itk::LightObject::Pointer itk::Hessian3DToVesselnessMeasureImageFilter< TPixel >::CreateAnother ( ) const

virtual

Create an object from an instance, potentially deferring to a factory. This method allows you to create an instance of an object that is exactly the same type as the referring object. This is useful in cases where an object has been cast back to a base class.

Reimplemented from itk::Object.