[ITK] [ITK-users] VariableLengthVector and multiplication

Dženan Zukić dzenanz at gmail.com
Wed Nov 22 12:42:44 EST 2017 

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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