[Insight-users] Perplexed with Optimizer initialization

[Luis Ibanez]

Hi Yu,


You are right,
parameters selection is a problem that is undersestimated by the
entire medical image community.

This disregards is closely related to the insufficiency of the
publishing system and to the lack of appreciation for the practice
of reproducibility of research work.

In other words:  since most published algorithms are not presented
in a form that is intended to make easier for other to reimplement
and run those algorithms, authors do not address the very important
issue of parameter selection. Authors are more interested in claiming
credit for the basic ideas behind their published algorithms.

In the real world, however, parameter selection is a challenge of a
larger scale than software development itself.


That being said....



Of, course, if you take an example, for which the paramters were
already adjusted... and you *change* the parameters... well... it
will not always work.


Since your question is quite generic,... we can only give you
a generic answer.  If you are interested in a more specific
answer.... please post a more specific question.


Generic answer:


In the selection of parameters for registration you wan to
do the following:


1) Make sure that the scaling array of parameter of the
   VersorRigid3D transform are in the range of

          1.0 for rotations
          1/(diagonal of the image in millimeters) for translation


2) Connect a command observer and print out the values
   of the metric and the paramters array at every iteration




3) Start with very small steps in the optimizer.
   E.g. in the range of 0.1



Note that Algorithms *do not* and *do not have to* work for
*every* arbitrary combination of parameters. So, you shouldnt
expect to take a fine tunned example and be able to move the
parameters at will while still getting reasonable results.


Otherwise...
well... there will not be any need for parameter fine tunning.





   Regards,



         Luis



--------------------
Yu Qi wrote:
> Hi everybody,
> I get to know ITK since only few months ago. I find it is a very well 
> orgnized toolkit for image registration and I made my only application 
> successfully!
>  
> But there is one thing always confuses me during my programming:
> the selection of parameters :-( . I first copy codes from user guide and 
> it worked. Then I want to change those parameters to see the influence 
> of them to the results. But it not alway turned out a success.
>  
> Does anyone can help me with how to configure those parameters, 
> optimizer and metric? What is the most important one which I should take 
> care first? What is the usual range of adjustment?
>  
> Or will somebody enclose a paper about optimizers to me?
>  
> Metric in my application: MattesMutualInformationImageToImageMetric
>                                      MutualInformationImageToImageMetric
> Optimizer I used: itkVersorRigid3DTransformOptimizer
>  
> Thank you all!
>  
>  
>  
>  
>  
> 
> 
> *Best Regards!*
> ** 
> *Yu Qi*
>  
>  
> 
> 
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