[Insight-users] itkRecursiveMultiResolutionPyramidImageFilter

[Luis Ibanez]

Hi Corinne,

Thanks for letting us know the result of your test.

This issue was entered as Bug# 503
http://www.itk.org/Bug/bug.php?op=show&bugid=503&pos=24

and it has been fixed in the repository.

If you updated your CVS checkout the line
SetUseImageSpacing() will be in the filter.


Please let us know if you find any further problem.


Thanks


    Luis


----------------------------
Corinne Mattmann wrote:

> Hi Luis,
> 
> I added the code you suggested and it's working fine for my image.
> 
> Thanks very much for your help,
> Corinne
> 
> 
> -----Original Message-----
> From: Luis Ibanez [mailto:luis.ibanez at kitware.com] 
> Sent: Thursday, January 08, 2004 8:18 PM
> To: Corinne Mattmann
> Cc: insight-users at itk.org; Lydia Ng
> Subject: Re: [Insight-users]
> itkRecursiveMultiResolutionPyramidImageFilter
> 
> 
> 
> Hi Corinne,
> 
> The reason why you are observing so much smoothing is
> that the RecursiveMultiResolutionPyramidImageFilter
> uses a DiscreteGaussianImageFilter internally in
> order to smooth the images before the subsampling.
> 
> The DiscreteGaussianImageFilter specifies its
> Variance in physical units, not in pixels.
> 
> Your image (BTW thanks for providing the spacing
> information) has a relatively small spacing = 0.09.
> 
> The typical value of Variance computed from the
> pyramid factors will be about 4.0, which for a
> CT or MRI image corresponds normally to a sigma
> of about 2 pixels wide.
> 
> In the case of your image, however, a Sigma of 2.0
> is equivalent to a kernel 20 pixels wide, which is
> obviously too large.
> 
> Maybe the solution is to disable the flag:
> 
>                  UseImageSpacing
> 
> in the smoothing filter, since the smoothing is being
> done based on the relative scale factor of the schedule
> rather than the physical size of the image pixels.
> 
> Please try adding
> 
>      smoother->SetUseImageSpacing( false );
> 
> in line 81.  In that way the values of Sigma will be interpreted as
> number of pixels instead of number of millimeters (or in general:
> physical units).
> 
> 
> Please let us know if that works for you, so we
> can make this change in the repository.
> 
> 
> 
> Thanks
> 
> 
> 
>     Luis
> 
> 
> 
> -----------------------
> Corinne Mattmann wrote:
> 
>>Hi,
>>
>>I'm using the itkRecursiveMultiResolutionPyramidImageFilter and I have
> 
> 
>>some problems with this filter: It seems that this filter smoothes my 
>>image that much before resampling, that I get an almost homogenous 
>>image. If I take the "smoother" out of the filter (  
>>shrinker->SetInput( caster->GetOutput() ); on line 83), then 
>>everything works fine. Also if I set the variance very small 
>>(variance[idim] = 0.01; on line 114) the result is okay. Can you 
>>explain me why this smoother is not working for my image and why the 
>>variance is chosen as it is?
>>
>>Thanks,
>>Corinne
>>
>>ps: I have a 50x50x50 image with origin {3.37776, 1.73713, 3.37776} 
>>and spacing {0.0965074, 0.0965074, 0.0965074}.
>>
>>_______________________________________________
>>Insight-users mailing list
>>Insight-users at itk.org 
>>http://www.itk.org/mailman/listinfo/insight-users
>>
> 
> 
> 
> 
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