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<p>Thanks. <br>
</p>
<p>Here is the solution I used, which works but may be sub-optimal:
<br>
</p>
<p>namespace Functor<br>
{<br>
template< class TPixel, class TInternal><br>
class DotProduct<br>
{<br>
public:<br>
DotProduct() {}<br>
~DotProduct() {}<br>
bool operator!=(const DotProduct &) const<br>
{<br>
return false;<br>
}<br>
<br>
bool operator==(const DotProduct & other) const<br>
{<br>
return !( *this != other );<br>
}<br>
<br>
template<typename T = TPixel><br>
inline<br>
typename itk::mpl::EnableIf<itk::mpl::IsSame<T,
TInternal>, TInternal>::Type<br>
operator()(const TInternal & A, const TInternal & B)
const<br>
{ return static_cast<TInternal>( A * B ); }<br>
<br>
template<typename T = TPixel><br>
typename itk::mpl::DisableIf<itk::mpl::IsSame<T,
TInternal>, TInternal>::Type<br>
operator()(const TPixel & A, const TPixel & B) const<br>
{<br>
TInternal out = 0;<br>
for (unsigned int component=0; component <
itk::NumericTraits<TPixel>::GetLength(A); component++)<br>
{<br>
out += A[component] * B[component];<br>
}<br>
return out;<br>
}<br>
};<br>
} // end namespace functor<br>
<br>
</p>
<br>
<div class="moz-cite-prefix">On 22/11/2017 18:42, Dženan Zukić
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAPf2UMQ6pi=FzyhHhR4hYQ2uPGHJ=zKAnkdSWmePRh7NZQib1A@mail.gmail.com">
<div dir="ltr">
<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small">I found
it. Construct is called <b>EnableIf</b>, and you can see how
it is used in <i>ITK\Modules\Core\Common\test\itkEnableIfTest.cxx</i></div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small">Regards</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, Nov 22, 2017 at 10:17 AM,
Dženan Zukić <span dir="ltr"><<a
href="mailto:dzenanz@gmail.com" target="_blank"
moz-do-not-send="true">dzenanz@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small">Hi
Cyril,</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small">Francois
has recently used compileif construct. That might help
you. But I can't find an instance of it right now.</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small">Also,
we are moving to <a href="https://discourse.itk.org/"
target="_blank" moz-do-not-send="true">discourse</a>.
Please post follow-ups there.</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small">Regards,</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small">Dženan</div>
</div>
<div class="HOEnZb">
<div class="h5">
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, Nov 22, 2017 at 9:54
AM, Cyril Mory <span dir="ltr"><<a
href="mailto:cyril.mory@creatis.insa-lyon.fr"
target="_blank" moz-do-not-send="true">cyril.mory@creatis.insa-lyon.<wbr>fr</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Thanks
for this answer.<br>
<br>
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).<br>
<br>
I found the "itk::NumericTraits<TPixel>::G<wbr>etLength()"
method, which works in both cases, and so I tried
this:<br>
<br>
<br>
namespace Functor<br>
{<br>
template< class TPixel, class TInternal><br>
class DotProduct<br>
{<br>
public:<br>
DotProduct() {}<br>
~DotProduct() {}<br>
bool operator!=(const DotProduct &) const<br>
{<br>
return false;<br>
}<br>
<br>
bool operator==(const DotProduct & other)
const<br>
{<br>
return !( *this != other );<br>
}<br>
<br>
inline TInternal operator()(const TPixel &
A, const TPixel & B) const<br>
{<br>
TInternal out = 0;<br>
for (unsigned int component=0; component <
itk::NumericTraits<TPixel>::Ge<wbr>tLength();
component++)<br>
{<br>
out += A[component] * B[component];<br>
}<br>
return out;<br>
}<br>
};<br>
} // end namespace functor<br>
<br>
<br>
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 ?<br>
<br>
Regards,<br>
Cyril
<div class="m_-4725059247121473243HOEnZb">
<div class="m_-4725059247121473243h5"><br>
<br>
On 22/11/2017 14:38, Lowekamp, Bradley
(NIH/NLM/LHC) [C] wrote:<br>
<blockquote class="gmail_quote"
style="margin:0 0 0 .8ex;border-left:1px
#ccc solid;padding-left:1ex">
Hello,<br>
<br>
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.<br>
<br>
As you indicate there are many possible
meanings for multiplication of vector
images, which can lead to confusion.<br>
<br>
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].<br>
<br>
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.<br>
<br>
<br>
Brad<br>
<br>
<br>
[1] <a
href="https://itk.org/Doxygen/html/classitk_1_1UnaryFunctorImageFilter.html"
rel="noreferrer" target="_blank"
moz-do-not-send="true">https://itk.org/Doxygen/html/c<wbr>lassitk_1_1UnaryFunctorImageFi<wbr>lter.html</a><br>
[2] <a
href="https://itk.org/Doxygen/html/classitk_1_1BinaryFunctorImageFilter.html"
rel="noreferrer" target="_blank"
moz-do-not-send="true">https://itk.org/Doxygen/html/c<wbr>lassitk_1_1BinaryFunctorImageF<wbr>ilter.html</a><br>
[3] <a
href="https://itk.org/Doxygen/html/classitk_1_1MultiplyImageFilter.html"
rel="noreferrer" target="_blank"
moz-do-not-send="true">https://itk.org/Doxygen/html/c<wbr>lassitk_1_1MultiplyImageFilter<wbr>.html</a><br>
[4] <a
href="https://itk.org/Doxygen/html/WikiExamples_2ImageProcessing_2BinaryFunctorImageFilter_8cxx-example.html#_a1"
rel="noreferrer" target="_blank"
moz-do-not-send="true">https://itk.org/Doxygen/html/W<wbr>ikiExamples_2ImageProcessing_2<wbr>BinaryFunctorImageFilter_8cxx-<wbr>example.html#_a1</a><br>
<br>
On 11/22/17, 5:15 AM, "Cyril Mory" <<a
href="mailto:cyril.mory@creatis.insa-lyon.fr"
target="_blank" moz-do-not-send="true">cyril.mory@creatis.insa-lyon.<wbr>fr</a>>
wrote:<br>
<br>
Dear ITK users,<br>
I am using itk::VectorImage in
some of my code, which uses<br>
itk::VariableLengthVector as pixel
type. And I am wondering why<br>
itk::VariableLengthVector has so little
support for multiplication.<br>
Currently, the * operator only supports
multiplication by a scalar.<br>
It probably isn't simple, but I
would need three additional kinds of<br>
multiplication:<br>
- dot product with another
VariableLengthVector (that has the same<br>
length, although it is probably a waste
of time to perform the check<br>
every time), returning a scalar<br>
- component-wise multiplication,
returning a VariableLengthVector of the<br>
same length<br>
- left or right multiplication
with a matrix (possibly an<br>
itk::VariableSizeMatrix) that has the
correct size, but I understand<br>
that this is probably the most complex
one, and since it only occurs<br>
rarely in my code, I can handle it with
conversions to vnl::vector and<br>
vnl::matrix<br>
Are there constraints that prevent
at least the dot product and<br>
component-wise multiplication operators
from being implemented ? If not,<br>
then I'd be happy to give it a try.
Since both differ only by the return<br>
type, two different operators would
have to be used (I guess). Do you<br>
have suggestions (which one should use
*, and what should be the other<br>
operator) ? In itk::Vector and
itk::CovariantVector, the * operator is<br>
used for dot product.<br>
Regards,<br>
Cyril<br>
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