[Insight-users] Perplexed with Optimizer initialization

Luis Ibanez luis.ibanez at kitware.com
Mon May 23 18:17:00 EDT 2005


Hi Yu,


If your image has number of pixels:

   (200,300,400) in x,y,z respectively

and the pixel spacing is:

   (0.3, 0.3, 0.7) millimeters in x,y,z respectively

then your image physical extent will be

   (   200 x 0.3, 300 x 0.3, 400 x 0.7 )

   =    ( 60, 90, 280 )

millimeters in x,y,z respectively


The 3D diagonal of that image will be

  square_root(  60^2 + 90^2 + 280^2 )

  =           300.16 millimeters


so the scaling that you want to put in the
tranlational part of your transform is:

       1.0 /  300.16




Note that this is just a good first value
to try. You may want to experiment by moving
it 10X or 0.lX.



Regards,



    Luis



-------------------
Yu Qi wrote:

> 
> 
> 注:已附加转发邮件。
> 
> 
> ------------------------------------------------------------------------
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> 
> ------------------------------------------------------------------------
> 
> Subject:
> Re: [Insight-users] Perplexed with Optimizer initialization
> From:
> Yu Qi <felix_china at yahoo.com.cn>
> Date:
> Fri, 20 May 2005 21:41:23 +0800 (CST)
> To:
> Luis Ibanez <luis.ibanez at kitware.com>
> 
> 
> Hi Luis,
> I'm not sure about
> "in the range of 1/(diagonal of the image in millimeters) for translation"
> you mentioned in your email.
>  
> For example, my diagonal is around 300mm
> which is the range? 0~300 or 300~300+?
>  
> There was somebody told it should be in the range of 50~300, is that 
> correct?
>  
> Best regards,
> Yu Qi
> 
> */Luis Ibanez <luis.ibanez at kitware.com>/* 写道:
> 
> 
> 
>     Hi Yu,
> 
> 
>     You are right,
>     parameters selection is a problem that is undersestimated by the
>     entire medical image community.
> 
>     This disregards is closely related to the insufficiency of the
>     publishing system and to the lack of appreciation for the practice
>     of reproducibility of research work.
> 
>     In other words: since most published algorithms are not presented
>     in a form that is intended to make easier for other to reimplement
>     and run those algorithms, authors do not address the very important
>     issue of parameter selection. Authors are more interested in claiming
>     credit for the basic ideas behind their published algorithms.
> 
>     In the real world, however, parameter selection is a challenge of a
>     larger scale than software development itself.
> 
> 
>     That being said....
> 
> 
> 
>     Of, course, if you take an example, for w! hich the paramters were
>     already adjusted... and you *change* the parameters... well... it
>     will not always work.
> 
> 
>     Since your question is quite generic,... we can only give you
>     a generic answer. If you are interested in a more specific
>     answer.... please post a more specific question.
> 
> 
>     Generic answer:
> 
> 
>     In the selection of parameters for registration you wan to
>     do the following:
> 
> 
>     1) Make sure that the scaling array of parameter of the
>     VersorRigid3D transform are in the range of
> 
>     1.0 for rotations
>     1/(diagonal of the image in millimeters) for translation
> 
> 
>     2) Connect a command observer and print out the values
>     of the metric and the paramters array at every iteration
> 
> 
> 
> 
>     3) Start with very small steps in the optimizer.
>     E.g. in the range of 0.1
> 
> 
> 
>     Note that Algorithms *do not* and *do not have to* work for
>     *every* arbitrary combination of parameters. So, you shouldnt
>     expect to ! take a fine tunned example and be able to move the
>     parameters at will while still getting reasonable results.
> 
> 
>     Otherwise...
>     well... there will not be any need for parameter fine tunning.
> 
> 
> 
> 
> 
>     Regards,
> 
> 
> 
>     Luis
> 
> 
> 
>     --------------------
>     Yu Qi wrote:
>      > Hi everybody,
>      > I get to know ITK since only few months ago. I find it is a very
>     well
>      > orgnized toolkit for image registration and I made my only
>     application
>      > successfully!
>      >
>      > But there is one thing always confuses me during my programming:
>      > the selection of parameters :-( . I first copy codes from user
>     guide and
>      > it worked. Then I want to change those parameters to see the
>     influence
>      > of them to the results. But it not alway turned out a success.
>      >
>      > Does anyone can help me with how to configure those parameters,
>      > optimizer and metric? What is the most important one which I
>     should take
>      >! ; care first? What is the usual range of adjustment?
>      >
>      > Or will somebody enclose a paper about optimizers to me?
>      >
>      > Metric in my application: MattesMutualInformationImageToImageMetric
>      > MutualInformationImageToImageMetric
>      > Optimizer I used: itkVersorRigid3DTransformOptimizer
>      >
>      > Thank you all!
>      >
>      >
>      >
>      >
>      >
>      >
>      >
>      > *Best Regards!*
>      > **
>      > *Yu Qi*
>      >
>      >
>      >
>      >
>      >
>     ------------------------------------------------------------------------
>      > *Do You Yahoo!?*
>      > 150万曲MP3疯狂搜,带您闯入音乐殿堂
>      > 美女明星应有尽有,搜遍美图、艳图和酷图
>      > 1G就是1000兆,雅虎电邮自助扩容!
>      >
>      >
>      >
>      >
>      >
>     ------------------------------------------------------------------------
>      >
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> 
> 
> 
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> 150万曲MP3疯狂搜,带您闯入音乐殿堂 <http://music.yisou.com>
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> <http://cn.rd.yahoo.com/mail_cn/tag/1g/*http://cn.mail.yahoo.com/event/mail_1g/> 
> 
> 
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