[Insight-developers] Change to itkMultiResolutionPyramidImageFilter.txx

Thu Mar 26 11:46:03 EDT 2009

Hello Hans,

	I don't see any definition for center of mass there. A discrete  
center of mass is usually defined as a  sum ( weight * location)/  
sum( weight ). I do not know if what you are intending weight to mean  
in your definition. I have been assuming that you are not referring to  
any, and all the weights are one. Therefore, better terminology may be  
"physical center" or "physical location of center". Which are you  
referring too?

If this was just a bug with the geometry, the Spacing and Origin meta  
data, then why were there changes to the sampling algorithms? I think  
that the geometry needs to be clearly explained some place.

In terms of a diagram I think that we need something equivalent to the  
Figure 4.1 in the Guide, but for resampling (perhaps only 1d). Are we  
assuming that there is a 1-to-1 mapping of all physical points between  
an original and a resampled image? This is where I see the heart of  
this problem.

I don't see how changing from nearest to linear interpolation is  
related. It seems more like change in behavior and output then this  
bug (the way I understand it).

Also if we look at the changes to Shrinker:
http://public.kitware.com/cgi-bin/viewcvs.cgi/Code/BasicFilters/itkShrinkImageFilter.txx?root=Insight&r1=1.54&r2=1.55&sortby=date
I have not looked at the  
itkShrinkImageFilter::GenerateOutputInformation method close enough to  
know what it's trying to do. I find the addition of the transform to  
be rather poor technique, and a reduction in the light weight  
performance this class previously had.

But the question still remains is changing from the Shrinker to a  
linear interpolated Resample filter really a bug? or is it a  
fundamental change in behavior?

Brad

On Mar 26, 2009, at 11:03 AM, Hans Johnson wrote:

> Brad,
>
> Look at the attachment to bug http://public.kitware.com/Bug/view.php?id=8275 
> .   This attachment includes the image and the description of center  
> of mass bug.
>
> Hans
> -- 
> Hans J. Johnson, Ph.D.
> Hans-johnson at uiowa.edu
>
> 278 GH
> The University of Iowa
> Iowa City, IA 52241
> (319) 353 8587
>
>
> From: Bradley Lowekamp <blowekamp at mail.nih.gov>
> Date: Thu, 26 Mar 2009 10:57:23 -0400
> To: Bill Lorensen <bill.lorensen at gmail.com>
> Cc: Luis Ibanez <luis.ibanez at kitware.com>, ITK <insight-developers at itk.org 
> >, Hans Johnson <hans-johnson at uiowa.edu>
> Subject: Re: [Insight-developers] Change to  
> itkMultiResolutionPyramidImageFilter.txx
>
> I am giving these changes a closer look. I don' think they were the  
> correct thing to do as they made a fundamental change in the  
> behavior of the Pyramids.
>
> http://www.itk.org/cgi-bin/viewcvs.cgi/Code/Algorithms/itkMultiResolutionPyramidImageFilter.txx?root=Insight&r1=1.25&r2=1.26&sortby=date
>
> Changing from the Shrinker (which used to be an optimized nearest  
> neighbor) to using a linear interpolated Resample seems wrong to me.
>
> I don't fully understand what the "center of mass" bug is. I think a  
> more documentation and a diagram is really needed, to describe the  
> behavior of resampling, and shrinking. This will prevent another bug  
> from happening again when the current behavior is not liked.
>
> Brad
>
> ps
> I could talk more about optimization of itkShrinkImageFilter has  
> been reduced too, but I think that is another subject.
>
>
> On Mar 25, 2009, at 4:33 PM, Bill Lorensen wrote:
>
>> Luis,
>>
>> This change
>>
>> http://www.itk.org/cgi-bin/viewcvs.cgi/Code/Algorithms/itkMultiResolutionPyramidImageFilter.txx?root=Insight&r1=1.29&r2=1.30&sortby=date
>>
>> should be added to the 3.10 release. This undoes the backward
>> compatibility I broke with a bad checkin on Dec 17
>> http://www.itk.org/cgi-bin/viewcvs.cgi/Code/Algorithms/itkMultiResolutionPyramidImageFilter.txx?root=Insight&r1=1.26&r2=1.27&sortby=date
>>
>> Bill
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>
> ========================================================
>
> Bradley Lowekamp
>
> Lockheed Martin Contractor for
>
> Office of High Performance Computing and Communications
>
> National Library of Medicine
>
> blowekamp at mail.nih.gov
>
>
>
>

========================================================
Bradley Lowekamp
Lockheed Martin Contractor for
Office of High Performance Computing and Communications
National Library of Medicine
blowekamp at mail.nih.gov

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