[Insight-users] itkExpectationMaximizationMixtureModel

[ahmad bukhari]

hi  jisung and others... 
The assignment of weightages is global and hence it shall not be effective 
..In a certain intensity zone a class may not be present at all and then 
assigning weightages does not help in any way.... 
An example of adding a component shall be useful for me. 
thanks 
ahmad 
----- Original Message -----  
From: Jisung Kim <bahrahm@yahoo.com>  
Date: Fri, 25 Oct 2002 07:11:31 -0700 (PDT)  
To: ahmad bukhari <highway_111@mail.com>, insight  
<insight-users@public.kitware.com>  
Subject: Re: [Insight-users] itkExpectationMaximizationMixtureModel  
  
  
> Hi ahmad,  
>   
>   
> --- ahmad bukhari <highway_111@mail.com> wrote:  
> >  hi everyone!!   
> > There is another issue that i need help with:   
> > the mixture model can finally give you an estimate  
> > of   
> > the different classes presence....but the trouble is  
> >   
> > that different classes occur in different intensity   
> > regions. For example in an intensity zone on  a  
> > typical   
> > frequency histogram plot different classes occur in   
> > different regions interfering in some cases and  
> > isolated   
> > in rest. So the mixture model perhaps should be  
> > applied   
> > (initialized)differently for different intensity  
> > zones   
> > to get an accurate picture. Is there a way out...??   
>   
> Each iteration of the EM estimation process updates  
> weights for measurement vectors with given  
> "components". In other words, in the test program,  
> each measurement vector has two weight values that  
> tells you how likely the measurement vector belongs to  
> the two Gaussian classes. When the Gaussian components  
> update  their parameters, they use the weights instead  
> of using simple mean and covariance calculations. This  
> weighted mean and weighted covariance calculations  
> actually has similar effect that you mentioned.  If a  
> measurement vector highly likely belong to a component  
> (let's say component A) but not to  the other  
> component (component B), then the measurement vector  
> will affects the parameter calculation of component A  
> but won't affect much that of component B.  
>   
> Is this what you need?  
>   
>     
>   
> > thanks   
> > ahmad     
> > --   
> >   
>   
> Thanks,  
>   
> Jisung.  
>   
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> =====  
> Jisung Kim  
> bahrahm@yahoo.com  
> 106 Mason Farm Rd.  
> 129 Radiology Research Lab., CB# 7515  
> Univ. of North Carolina at Chapel Hill  
> Chapel Hill, NC 27599-7515  
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