[Insight-developers] Scales estimation for registration

Mon May 9 19:33:21 EDT 2011

Yeah, both are relevant and important. It is reasonable in ITK that we separate parameter scales from the learning rate. In my understanding, the former defines the relative impacts among parameters. The latter is more directly related to the step size. 

Baohua
  ----- Original Message ----- 
  From: Bill Lorensen 
  To: Baohua Wu 
  Cc: brian avants ; Nicholas Tustison ; Stefan Klein ; Marius Staring (registration) ; Stefan Klein ; Insight Developers 
  Sent: Monday, May 09, 2011 5:31 PM
  Subject: Re: [Insight-developers] Scales estimation for registration

  My concern is the estimation of the translation scales. It seems the global scale factor is used to scale the "estimated scales". I guess, indirectly, it interacts with the learning rate. So it is also of concern.

  On Mon, May 9, 2011 at 1:42 PM, Baohua Wu <baowu99 at gmail.com> wrote:

    hi brian,

    thank you for the information.

    to my knowledge, the test was passed with the synthetic data, and the scales worked well with several real images. i think bill's conern was mainly about how to set the global factor (or learning rate).

    we have been trying to estimate this global factor as well. some strategies include the norm of gradient, the parameter space, etc.

    baohua

    ----- Original Message ----- From: "brian avants" <stnava at gmail.com>
    To: "Baohua Wu" <baowu99 at gmail.com>; "Nicholas Tustison" <ntustison at gmail.com>
    Cc: "Stefan Klein" <s.klein at erasmusmc.nl>; "Bill Lorensen" <bill.lorensen at gmail.com>; "Marius Staring (registration)" <M.Staring at lumc.nl>; "Stefan Klein" <stefan at isi.uu.nl>; "Insight Developers" <insight-developers at itk.org>
    Sent: Monday, May 09, 2011 10:05 AM

    Subject: Re: [Insight-developers] Scales estimation for registration

    hi baohua

    nick may have some code that is relevant.

    also, you may want to let people know about your other strategies for
    estimating the parameter scales.  for instance,  the methods that take
    into account the norm of the gradient itself, as well as as that build
    estimates of the parameter space.

    brian

    On Mon, May 9, 2011 at 9:24 AM, Baohua Wu <baowu99 at gmail.com> wrote:

      Stefan,

      Thank you for the advice. I am glad to know your method works for scales
      and learning rate. I will try it .

      Baohua

      ----- Original Message ----- From: "Stefan Klein" <s.klein at erasmusmc.nl>
      To: "Bill Lorensen" <bill.lorensen at gmail.com>
      Cc: "Marius Staring (registration)" <M.Staring at lumc.nl>;
      <baowu99 at gmail.com>; "Stefan Klein" <stefan at isi.uu.nl>; "Insight Developers"
      <insight-developers at itk.org>
      Sent: Monday, May 09, 2011 7:43 AM
      Subject: Re: [Insight-developers] Scales estimation for registration

        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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