[Insight-developers] Scales estimation for registration

[Bill Lorensen]

Stefan,

I think the GlobalScalingFactor is a value to normalize the computed scales.
I'll take a look at your method.

Thanks,

Bill

On Mon, May 9, 2011 at 7:43 AM, Stefan Klein <s.klein at erasmusmc.nl> wrote:

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