[ITK] [ITK-users] VariableLengthVector and multiplication

Dženan Zukić dzenanz at gmail.com
Fri Nov 24 08:46:05 EST 2017 

That looks about right. Thanks for sharing your solution.

Regards,
Dženan

On Fri, Nov 24, 2017 at 6:54 AM, Cyril Mory <cyril.mory at creatis.insa-lyon.fr
> wrote:

> Thanks.
>
> Here is the solution I used, which works but may be sub-optimal:
>
> namespace Functor
> {
>   template< class TPixel, class TInternal>
>   class DotProduct
>   {
>   public:
>     DotProduct() {}
>     ~DotProduct() {}
>     bool operator!=(const DotProduct &) const
>     {
>       return false;
>     }
>
>     bool operator==(const DotProduct & other) const
>     {
>       return !( *this != other );
>     }
>
>   template<typename T = TPixel>
>   inline
>   typename itk::mpl::EnableIf<itk::mpl::IsSame<T, TInternal>,
> TInternal>::Type
>   operator()(const TInternal & A, const TInternal & B) const
>   { return static_cast<TInternal>( A * B ); }
>
>   template<typename T = TPixel>
>   typename itk::mpl::DisableIf<itk::mpl::IsSame<T, TInternal>,
> TInternal>::Type
>   operator()(const TPixel & A, const TPixel & B) const
>     {
>     TInternal out = 0;
>     for (unsigned int component=0; component < itk::NumericTraits<TPixel>::GetLength(A);
> component++)
>       {
>       out += A[component] * B[component];
>       }
>     return out;
>     }
>   };
> } // end namespace functor
>
>
> On 22/11/2017 18:42, Dženan Zukić wrote:
>
> I found it. Construct is called *EnableIf*, and you can see how it is
> used in *ITK\Modules\Core\Common\test\itkEnableIfTest.cxx*
>
> Regards
>
> On Wed, Nov 22, 2017 at 10:17 AM, Dženan Zukić <dzenanz at gmail.com> wrote:
>
>> Hi Cyril,
>>
>> Francois has recently used compileif construct. That might help you. But
>> I can't find an instance of it right now.
>>
>> Also, we are moving to discourse <https://discourse.itk.org/>. Please
>> post follow-ups there.
>>
>> Regards,
>> Dženan
>>
>> On Wed, Nov 22, 2017 at 9:54 AM, Cyril Mory <
>> cyril.mory at creatis.insa-lyon.fr> wrote:
>>
>>> Thanks for this answer.
>>>
>>> I am trying the approach you suggested, and would like to write a dot
>>> product functor that would work either on scalars (in which case it would
>>> perform a simple product) or on itk::VariableLengthVector of scalars (in
>>> which case it would perform a dot product).
>>>
>>> I found the "itk::NumericTraits<TPixel>::GetLength()" method, which
>>> works in both cases, and so I tried this:
>>>
>>>
>>> namespace Functor
>>> {
>>>   template< class TPixel, class TInternal>
>>>   class DotProduct
>>>   {
>>>   public:
>>>     DotProduct() {}
>>>     ~DotProduct() {}
>>>     bool operator!=(const DotProduct &) const
>>>     {
>>>       return false;
>>>     }
>>>
>>>     bool operator==(const DotProduct & other) const
>>>     {
>>>       return !( *this != other );
>>>     }
>>>
>>>     inline TInternal operator()(const TPixel & A, const TPixel & B) const
>>>     {
>>>     TInternal out = 0;
>>>     for (unsigned int component=0; component <
>>> itk::NumericTraits<TPixel>::GetLength(); component++)
>>>       {
>>>       out += A[component] * B[component];
>>>       }
>>>     return out;
>>>     }
>>>   };
>>> } // end namespace functor
>>>
>>>
>>> But it does not compile with itk::Image inputs, since the pixels A and B
>>> have no [ ] operator. Is there a standard way around this problem ?
>>>
>>> Regards,
>>> Cyril
>>>
>>>
>>> On 22/11/2017 14:38, Lowekamp, Bradley (NIH/NLM/LHC) [C] wrote:
>>>
>>>> Hello,
>>>>
>>>> There are an incredible number of different per-pixel operations that
>>>> could be implemented as ITK filters. We cannot provide them all. Many of
>>>> the basic operations are implemented as ITK filters these include
>>>> performing the basic C++ operators, such as +, -, * and /, on a per-pixel
>>>> basis.
>>>>
>>>> As you indicate there are many possible meanings for multiplication of
>>>> vector images, which can lead to confusion.
>>>>
>>>> ITK has a flexible set of Unary[1], Binary[2] functor filters. Classes
>>>> like the MultiplyImageFilter[3], are implemented by deriving from the base
>>>> functor classes. However it is easier to just use the base functor filter
>>>> and set the proper or custom functor, as in this example [4].
>>>>
>>>> It is fairly easy to write a functor for your specific purposes by
>>>> following the existing set [5]. It is common for filters to internally
>>>> define a private functor to perform one step in a large filter. Moving from
>>>> writing for loops on pixels to writing custom functors is part of good
>>>> usage of ITK.
>>>>
>>>>
>>>> Brad
>>>>
>>>>
>>>> [1] https://itk.org/Doxygen/html/classitk_1_1UnaryFunctorImageFi
>>>> lter.html
>>>> [2] https://itk.org/Doxygen/html/classitk_1_1BinaryFunctorImageF
>>>> ilter.html
>>>> [3] https://itk.org/Doxygen/html/classitk_1_1MultiplyImageFilter.html
>>>> [4] https://itk.org/Doxygen/html/WikiExamples_2ImageProcessing_2
>>>> BinaryFunctorImageFilter_8cxx-example.html#_a1
>>>>
>>>> On 11/22/17, 5:15 AM, "Cyril Mory" <cyril.mory at creatis.insa-lyon.fr>
>>>> wrote:
>>>>
>>>>      Dear ITK users,
>>>>           I am using itk::VectorImage in some of my code, which uses
>>>>      itk::VariableLengthVector as pixel type. And I am wondering why
>>>>      itk::VariableLengthVector has so little support for multiplication.
>>>>      Currently, the * operator only supports multiplication by a scalar.
>>>>           It probably isn't simple, but I would need three additional
>>>> kinds of
>>>>      multiplication:
>>>>           - dot product with another VariableLengthVector (that has the
>>>> same
>>>>      length, although it is probably a waste of time to perform the
>>>> check
>>>>      every time), returning a scalar
>>>>           - component-wise multiplication, returning a
>>>> VariableLengthVector of the
>>>>      same length
>>>>           - left or right multiplication with a matrix (possibly an
>>>>      itk::VariableSizeMatrix) that has the correct size, but I
>>>> understand
>>>>      that this is probably the most complex one, and since it only
>>>> occurs
>>>>      rarely in my code, I can handle it with conversions to vnl::vector
>>>> and
>>>>      vnl::matrix
>>>>           Are there constraints that prevent at least the dot product
>>>> and
>>>>      component-wise multiplication operators from being implemented ?
>>>> If not,
>>>>      then I'd be happy to give it a try. Since both differ only by the
>>>> return
>>>>      type, two different operators would have to be used (I guess). Do
>>>> you
>>>>      have suggestions (which one should use *, and what should be the
>>>> other
>>>>      operator) ? In itk::Vector and itk::CovariantVector, the *
>>>> operator is
>>>>      used for dot product.
>>>>           Regards,
>>>>           Cyril
>>>>                The ITK community is transitioning from this mailing
>>>> list to discourse.itk.org. Please join us there!
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>>>>
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>>
>>
>
>
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