[Insight-users] How to multiply a vector image by a constant

[Glen Lehmann]

Once again, thank you Luis.  I wanted to confirm that I wasn't  
overlooking an existing filter.

Thanks for the example,
Glen

On Thursday, January 22, 2004, at 02:20  PM, Luis Ibanez wrote:

> Hi Glen,
>
> ITK currently doesn't have a simple filter for
> multiplying a vector image by a constant,..
> but you can fabricate one in 10 minutes from the
> itkCastVectorImageFilter. Actually, here is one
> filter attached that should do the job.
>
> In general, for any pixel-wise operation you can
> simply look at using the UnaryFunctorFilter and
> define your own Functor as template parameter.
>
> ---
>
> An alternative option is to use ImageAdaptors.
> You will find examples of ImageAdaptors in the
> SoftwareGuide
>
>    http://www.itk.org/ItkSoftwareGuide.pdf
>
> Chapter 12, pdf-page 521. In particular, look
> at the vectorial examples in Section 12.3 and
> the computation example in section 12.4.
>
> The great advantage of image adaptors is that
> you don't pay for the memory overhead of storing
> a new vector image, just because you multiply the
> values by a constant.
>
> The PixelAccessor will look like:
>
>
> class VectorScalePixelAccessor
> {
> public:
>   typedef itk::Vector<float,3>   InternalType;
>   typedef itk::Vector<float,3>   ExternalType;
>
>   void operator=( const VectorPixelAccessor & vpa )
>     {
>       m_Factor = vpa.m_Factor;
>     }
>   ExternalType Get( const InternalType & input ) const
>     {
>       return ( input * m_Factor );
>     }
>   void SetFactor( double factor )
>     {
>       m_Factor = factor;
>     }
> private:
>   double  m_Factor;
> };
>
>
>
> Then, as shown in the software guide you create
> the ImageAdaptor by using the PixelAccessor as
> template argument.
>
>
>   typedef itk::ImageAdaptor<
>                       VectorImageType,
>                       VectorPixelAccessor
>                                > ImageAdaptorType;
>
>
> Then you create the accessor,
> set the factor value
> and pass it to the adaptor
>
>
>   VectorScalePixelAccessor  accessor;
>   accessor.SetFactor( 12345.0 );
>   adaptor->SetPixelAccessor( accessor );
>
>
> and simply plug the adaptor as input to the
> next filter in the pipeline.
>
>
> Note that adaptors look like images, not like
> filters, so there is no need for GetOutput() when
> you connect the adaptor to the next filter in the
> pipeline.
>
>
>
> Regards,
>
>
>   Luis
>
>
> ---------------------
> Glen Lehmann wrote:
>
>> Hello,
>> Sorry, I couldn't find an answer for this one in the archives.
>> I have a VectorImageType defined as;
>> typedef   double  PixelType;
>> typedef   itk::Vector< PixelType, 2 > VectorType;
>> typedef   itk::Image< PixelType, 2 >  ImageType;
>> typedef   itk::Image< VectorType, 2 >  VectorImageType;
>> I need to multiply my VectorImage by a constant.  If I were using  
>> ImageType I chould use the ShiftScaleImageFilter and set Scale as my  
>> constant.  I have tried the following with the VectorImageType;
>> typedef   itk::ShiftScaleImageFilter < VectorImageType,  
>> VectorImageType  > ShiftScaleFilterType;
>> The following line causes the compilere to complain that RealType is  
>> not defined;
>> ShiftScaleFilterType::Pointer NegativeVectorImage =  
>> ShiftScaleFilterType::New();
>> Any suggestions as to how to multiply my VectorImageType by a  
>> constant would be appreciated.
>> Thank you,
>> Glen
>> _______________________________________________
>> Insight-users mailing list
>> Insight-users at itk.org
>> http://www.itk.org/mailman/listinfo/insight-users
> --------------------------------------------------------
>
>
>
>
>
>
> / 
> *====================================================================== 
> ===
>
>   Program:   Insight Segmentation & Registration Toolkit
>   Module:    $RCSfile: itkVectorScaleImageFilter.h,v $
>   Language:  C++
>   Date:      $Date: 2003/09/10 14:28:59 $
>   Version:   $Revision: 1.10 $
>
>   Copyright (c) Insight Software Consortium. All rights reserved.
>   See ITKCopyright.txt or http://www.itk.org/HTML/Copyright.htm for  
> details.
>
>      This software is distributed WITHOUT ANY WARRANTY; without even
>      the implied warranty of MERCHANTABILITY or FITNESS FOR A  
> PARTICULAR
>      PURPOSE.  See the above copyright notices for more information.
>
> ======================================================================= 
> ==*/
> #ifndef __itkVectorScaleImageFilter_h
> #define __itkVectorScaleImageFilter_h
>
> #include "itkUnaryFunctorImageFilter.h"
>
> namespace itk
> {
>
> /** \class VectorScaleImageFilter
>  *
>  * \brief Multiplies input vector pixels by a constant factor and  
> produces
>  * as output an image of vector pixel type.
>  *
>  * The filter expect both images to have the same number of dimensions,
>  * and that both the input and output have itk::Vector pixel types
>  * of the same VectorDimension.
>  *
>  * \sa Vector
>  *
>  * \ingroup IntensityImageFilters  Multithreaded
>  */
> namespace Functor {
>
> template< class TInput, class TOutput>
> class VectorScale
> {
> public:
>   VectorScale() {}
>   ~VectorScale() {}
>   inline TOutput operator()( const TInput & A ) const
>   {
>     typedef typename TOutput::ValueType OutputValueType;
>
>     TOutput value;
>     for( unsigned int k = 0; k < TOutput::Dimension; k++ )
>       { value[k] = static_cast<OutputValueType>( A[k] * m_Factor ); }
>     return value;
>   }
>   void SetFactor( double factor )
>     {
>     m_Factor = factor;
>     }
>
> private:
>   double m_Factor;
> };
> }
>
> template <class TInputImage, class TOutputImage>
> class ITK_EXPORT VectorScaleImageFilter :
>     public
> UnaryFunctorImageFilter<TInputImage,TOutputImage,
>                         Functor::VectorScale< typename  
> TInputImage::PixelType,
>                                              typename  
> TOutputImage::PixelType>   >
> {
> public:
>   /** Standard class typedefs. */
>   typedef VectorScaleImageFilter  Self;
>   typedef UnaryFunctorImageFilter<TInputImage,TOutputImage,
>                                   Functor::VectorScale< typename  
> TInputImage::PixelType,
>                                                        typename  
> TOutputImage::PixelType> >  Superclass;
>   typedef SmartPointer<Self>   Pointer;
>   typedef SmartPointer<const Self>  ConstPointer;
>
>   /** Method for creation through the object factory. */
>   itkNewMacro(Self);
>
>   /** factor to use for multiplying the vectors */
>   void SetFactor( double factor )
>    {
>    this->GetFunctor().SetFactor( factor );
>    }
>
> protected:
>   VectorScaleImageFilter() {}
>   virtual ~VectorScaleImageFilter() {}
>
> private:
>   VectorScaleImageFilter(const Self&); //purposely not implemented
>   void operator=(const Self&); //purposely not implemented
>
> };
>
> } // end namespace itk
>
>
> #endif