[Insight-users] How to make NMI faster?

[Josem]

Hello I am looking for ways on how to make NMI run faster; the implementation
in :
"itkNormalizedMutualInformationHistogramImageToImageMetric.h"
is slow and we need something that could run  faster.

This is a follow up of this earlier thread:
http://itk-users.7.n7.nabble.com/Modifying-Mattes-MI-to-provide-a-Normalized-MI-td30155.html#a30166

I found this post earlier:
http://public.kitware.com/pipermail/insight-users/2006-May/017911.html
but it seems outdated, It says that I should modify the lines 815-832, but
in today's implementation the code is different.

So I am modifying Mattes MI by changing the following line: 
 //sum += jointPDFValue * ( pRatio - vcl_log(fixedImagePDFValue) ); 
  
with this one: 
sum +=
vcl_log(fixedImagePDFValue*movingImagePDFValue)/vcl_log(jointPDFValue); 

This modification looks like a good practical way of calculating the
normalized mutual information, using the
itkMattesMutualInformationImageToImageMetric.hxx implementation.

Please feel free to share any thoughts or suggestions.
thanks in advance.
Jose



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