[Insight-users] windows-linux

[Luis Ibanez]

Hi Maribel,

This is a known behavior.

It is not good, but it is normal  :-)

The reason is that MutualInformation uses a random iterator
in order to sample pixel values.  The random number generator
used by this iterators turns out to be different in Unix and
Windows systems.  This makes impossible for the algorithm to
behave in the same way on both Windows and Unix systems.

That being said, the result shouldn't be completely different.
You should only observe a different path in the parametric space,
and probably small differences in the final registration value.

If you are obtaining totally different results, that probably
indicates that other settings in the registration methods are
in critical conditions.  The usual suspects are the step length
of the RegularStepGradientDescent optimizer, the learning rate
of the GradientDescentOptimizer, the translation scaling parameters,
and the noise of the image itself.

The experimental way to find if you are using parameters close
to a critical range, is to tweak their values and see how much
this affects the results of the registration.

You could also preprocess the images with EdgePreserving filters
as described in the SoftwareGuide.


If you feel adventurous and motivated you could also plug in
your own random number generator in the RandomImageIterator
http://www.itk.org/Insight/Doxygen/html/classitk_1_1ImageRandomIteratorWithIndex.html
in order to make sure that it will behave in the same way in
any system.  Note also that there is a seen initialization
involved...

Since the current random number generator used in this iterator is
taken from VXL/VNL, there have been some talk among ITK developers
for getting a portable random number generator into VXL.  This will
be the real long term solution,... but it may not happen for a while.



    Regards,


       Luis


----------------------------
Adame, I.M. (LKEB) wrote:

> Hi everybody,
> 
> I am trying to run a registration procedure based on mutual information(it
> is the one provided as an example, with a few modifications). I need to have
> it in both environments: windows and linux. My problem is that I obtain
> completely different results from each of them for the same images.
> I think that it may have something to do with internal settings, but I don't
> know which. Does anyone have any idea about what my problem can be?
> Thank you very much.
> 
> Maribel Adame
> 
> 
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