[Insight-users] Speed increase in registration methods

[Luis Ibanez]

Hi Mark,

This is one of those situations where we have to
choose between performance and flexibility.

If we adopt the FixedArray as the carrier of the
Transform parameters, this means the transform type
must be used at compile time, because the dimension
of the FixedArray is a template parameters and must
therefore be known at compilation time.

Therefore, we should get back to a previous (2 or
3 years old) implementation of the Registration framework
where all the components were implemented using Generic
Programming.


The current implementation offers run-time flexibility
at the expense of performance. That is, it allows you
to change the Transform type at run-time and will adapt
to your change because the size of the Array is defined
at run time.

So, to summarize: the change of Array for FixedArray can
be done, but it will require a complete refactoring of the
registration methods.  It is not just changing the Metrics,
it also include refactoring all the Transform and all the
Optimizers.



The bottom line question is:

What do ITK users prefer ?

           speed   or    flexibility.




Regards,



     Luis



-------------------------------
Mark Wyszomierski wrote:

> Hi,
> 
> I was looking to speed up some of the registrations methods I'm using
> from ITK. I came across these threads in the mailing list:
> 
> http://public.kitware.com/pipermail/insight-users/2002-May/000448.html
> 
> in which Mr. Hannu says he received a 7 fold speed increase in the
> mutual information registration method by replacing itk::Array 's with
> itk::FixedArray 's.
> 
> I was just wondering if the later releases of ITK have incorporated
> this discovery(this thread is from 2002), and if it is possible to
> implement this substitution in other registration methods?
> 
> Thanks
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