[Insight-developers] Scales estimation for registration

[Stefan Klein]

Hi Bill,

The method in elastix works well in my experience.

The method is explained here:
http://dx.doi.org/10.1007/s11263-008-0168-y

Equation 61/62
But that final expression should be squared because of the definition of 
the scales in ITK.

The method needs to know the fixed image domain and the transform. So it 
would fit in the same framework as Bao's class. The methods declared at 
lines 147 to 161 should probably be protected by the way?

Just to clarify: the AutomaticScalesEstimation in elastix only computes 
the scales, not the global LearningRate. I guess the GlobalScalingFactor 
serves to determine the global LearningRate?

To automatically determine an optimal global learning rate, you would 
need the CostFunction as well. (since multiplying the costfunction by 10 
would cause the optimal learning rate to be divided by 10, for example).

Good idea to make this a separate class!
Kind regards,
Stefan



On 06/05/2011 22:52, Bill Lorensen wrote:
> Marius, Stefan and Bao,
>
> One of the major weaknesses in ITK's registration framework is the
> estimation of parameters. In particular, the estimation of the scales
> seems to require special magic. My experience has been that the
> selection of a proper scaling for translation is particularly
> difficult. ITK traditionally (and currently) leaves the scaling
> decision up to the application. There are currently two possible
> approaches to this estimation.
>
> 1) Bao's itkParameterScaleEstimator proposed in this gerrit topic:
> http://review.source.kitware.com/#change,1499
> 2) Elastix's (http://elastix.isi.uu.nl/) AutomaticScalesEstimation
>     method implementation in elxTransformBase.
>
> For Marius and Stefan I have questions:
>
> a) How successful is elastix's AutomaticScalesEstimation?
> b) Currently this is implemented as a method in
>     elxTransformBase. Could it be implemented in an API similar to Bao's
>     itkParameterScaleEstimator?
>
>
> For Bao's implementation, my concern is the addition of a free
> parameter GlobalScalingFactor. It is not clear how to pick a proper
> value. To me there is as much mystery in this parameter as there is in
> picking a proper translation scaling
>
> Bill
>
>
>
>
>
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
>
> Kitware offers ITK Training Courses, for more information visit:
> http://kitware.com/products/protraining.html
>
> Please keep messages on-topic and check the ITK FAQ at:
> http://www.itk.org/Wiki/ITK_FAQ
>
> Follow this link to subscribe/unsubscribe:
> http://www.itk.org/mailman/listinfo/insight-developers

-- 
Stefan Klein
+31 10 7043049
http://www.bigr.nl/people/StefanKlein