[Insight-users] mutual information measure

[J. Van Dalen]

THANKS!!! That helps a lot!!!

I tried to find some information on GetValue(), but without success. Can
you tell me how optimizer->GetValue() is computed. What is the "exact"
meaning of it. It is not the value of the cost function, nor the value of
its derivative (wrt some transformation parameter)... 

Moreover, can I just get this value after applying the registration? Doing
some simple tests it seems that - in general - the higher this value, the
better the registration.

Thanks again,
Jorn.

> The loop of iterations on Registration methods is controled
> by the optimizers. Metrics are used as the cost function to
> be optimized.
> 
> It may be easier to get the value directly from the Optimizer,
> just using its "GetValue()" method.
> 
> Note that only the value returned by the optimizer can be taken
> as an indication of the evolution of the registration method.
> Printing out the values computed by the metric can be misleading
> because some optimizers compute derivatives by finite differences.
> This implies that the metric "GetValue()" method is called several
> times just to compute the derivative.
> 
> The "GetValue()" returned by the optimizer is the values that
> is actually used to control convergence and eventually stop the
> optimization process.
> 
> BTW,
> The sensitivity to parameters is unfortunately quite common
> on registration. There is a need for smarter methods to figure
> out good combinations of parameters. You could imaging neural
> networks or maybe fuzzy logic systems built on top of registration
> methods for a next generation of software.
> 
> 
> Please let us know if you have futher questions,
> 
> 
>     Thanks
> 
> 
>        Luis
> 
> 
> 
> -------------------------------
> 
> J. Van Dalen wrote:
> 
> > Dear itk-users,
> > 
> > I use itkMutualInformationImageToImageMetric to perform a registration. It
> > all seems to work: I do not get error messages and by eye the two images
> > seem to be on top of each other. However, the result depends very much on
> > the value of the inputparameters (translateScale, numberOfIterations
> > learningRate, standardDeviation, numberOfSamples). Now, I would like to
> > tune these parameters to get an optimal result. Therefore, I would like to
> > have some kind of a mutual information measure, that indicates how well
> > the registration is performed. I already try to use GetValueAndDerivative
> > in itkMutualInformationImageToImageMetric, but it doesn't give me any
> > relevant information (I only observe fluctuations after each iteration).
> > 
> > Has anybody an idea? Is there something available in the itk routines
> > that I overlooked?
> > 
> > Regards,
> > Jorn.
> > 
> > 
> > 
> > _______________________________________________
> > Insight-users mailing list
> > Insight-users@public.kitware.com
> > http://public.kitware.com/mailman/listinfo/insight-users
> > 
> > 
> 
> 
> 
> 

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----Jorn van Dalen------------------------Physicist, PhD-----------------
----UMCN St. Radboud----------------------Room: 0.141--------------------
----Dept. Radiology-----------------------Telephone: +31 24 361 4766-----
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