[Insight-users] Ref: Multi-resolution registration : how to speed up.

[Luis Ibanez]

Hi Liqin,

It is normal for the first and last slices to
be incomplete. Since this is a 3D registration,
any slight rotation in space will make the two
volumes not to be aligned. Then, when resampling,
some of the pixels will fall off the moving image
extent.

About your two other questions

1) I'm not sure I understand this question.
    Are you refering to itk objects created in memory ?
    Are you refering to files created on disk ?
    Could you please be more specific.

2) You certainly can cut the computation time.
    This setup for image registration usually doesn't
    stop by convergence to a local region of the
    parameter space. In practice it tends to use all
    the iterations you allowed.  You may want to
    add Observers to the registration method and
    track the evolution of the optimizer in the
    parameter space. A plot of the movements in
    the parameter space will let you know when the
    optimizer has made enough iterations at a certain
    pyramid level.  A very slow movement on the parameter
    space will indicate that learning rates are two low.
    Small learning rates penalize computational time simply
    because you need more steps to move the same distance.

    With this insight you can fine tune the number of
    iterations as well as the learning rates at each
    level of the pyramid.

    A detailed example on how to add an Observer to a
    registration method is available on the file:

    Insight/Examples/Registration/ImageRegistration3.cxx

    you may also want to take a look at the CommandIterationUpdate
    class in

    Insight/Testing/Code/Algorithms

    This class is used to monitor the evolution of most
    of the ImageRegistrationMethodTest_*.cxx programs in
    this same directory.



Please let us know if you have further questions.

   Thanks


     Luis


-------------------------------
Wang, Liqin wrote:
> Luis,
> 
> Thanks for the information. It really helps.
> Now I have another question:
>  The first few images slices are not complete. Please see the attached file. <<register000.pgm>> 
> 
> Other questions are:
> 
> 1). The program created certain amount of objects, I am wondering when these objects get deleted from the system?
> 2). To run this program still took about 15 mins, is there any way to further speed it?
> 
> Thanks,
> 
> Liqin
> 
>