[ITK] [ITK-users] VariableLengthVector and multiplication

Wed Nov 22 08:38:41 EST 2017

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_1UnaryFunctorImageFilter.html
[2] https://itk.org/Doxygen/html/classitk_1_1BinaryFunctorImageFilter.html
[3] https://itk.org/Doxygen/html/classitk_1_1MultiplyImageFilter.html
[4] https://itk.org/Doxygen/html/WikiExamples_2ImageProcessing_2BinaryFunctorImageFilter_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

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Kitware offers ITK Training Courses, for more information visit:
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