[Insight-developers] Re: [Insight-users] concept checking in AccumulateImageFilter

Gaetan Lehmann gaetan.lehmann at jouy.inra.fr
Thu Mar 16 04:22:09 EST 2006 

Hi,

The code is modified - are perhaps I should say rewritten at this point -  
and now accept both N and N-1 dimensions for output image.
Please, look at  
http://insight-journal.org/view_reviews.php?back=publications.php%3Fjournalid%3D4%26order%3D%26revision_display%3D&pubid=71  
.
It would also be nice if you can test the code, and post a review.

Regards,

Gaetan


On Thu, 16 Mar 2006 03:02:36 +0100, Alberto Bert <bert at isi.it> wrote:

> Hi,
>
> I'm one of the people that is using that filter and as Luis poited
> out, it would be resonable to have a N-1 output image dimension.
> Right now, I'm just casting the output to reduce the dimension.
>
> Are you gus planning to change the code or not?
>
> Cheers
> Alberto
>
> On Mar 02, 2006 at 11:22:01AM +0100, Gaetan Lehmann wrote:
>>
>> Hi,
>>
>> I have checked the AccumulateImageFilter code, and reduce a dimension  
>> will
>> work properly only if the dimension is the last one.
>>
>> The wanted behavior is, I think, the following one: the dimension which  
>> is
>> removed must take the place of the projection dimension.
>>
>> For example, for 3D -> 2D:
>> . projection dim=0
>>  1->1
>>  2->0
>> . projection dim=1
>>  0->0
>>  2->1
>> . projection dim=2
>>  0->0
>>  1->1
>>  in that case, there is nothing special: the projected dimension is the
>> removed one
>>
>> AccumulateImageFilter do not take care of that, and so, for 3D to 2D,  
>> only
>> the projection on the dimension 2 will work properly.
>>
>> Gaetan
>>
>>
>>
>> On Thu, 02 Mar 2006 01:46:37 +0100, Casey Goodlett <gcasey at gmail.com>
>> wrote:
>>
>> >Hello,
>> >
>> >I was the person who initially reported this difficulty to Amy.  I have
>> >existing code that uses the AccumulateImageFilter to find the mean of
>> >several volumes stacked into a 4D dataset from the TileImageFilter.  I
>> >have
>> >several 3D vector image volumes which I stack into a 4D volume using
>> >TileImageFilter, and then I use the accumulate filter to find the mean  
>> 3D
>> >volume.  Requiring the mean image to remain in 4D requires the headache
>> >of
>> >further processing to reduce it to a 3D volume.  The AccumulateFilter
>> >already works for me in going from ND to (N-1)D so there are no code
>> >changes
>> >required.
>> >
>> >Can the concept check allow either the same dimension or one less,
>> >because
>> >people may already be using either of these conventions?  I dont think
>> >enforcing either one exclusively is a good idea in terms of backwards
>> >compatibility.
>> >
>> >I can provide sample code if necessary, but I'd need to extract it  
>> from a
>> >larger project.
>> >
>> >Casey Goodlett
>> >
>> >On 3/1/06, Luis Ibanez <luis.ibanez at kitware.com> wrote:
>> >>
>> >>
>> >>Hi Gaetan,
>> >>
>> >>We agree with you that according to the Doxygen documentation
>> >>of the filter, the dimensions of the input image and the output
>> >>image should be the same.
>> >>
>> >>
>> >>However, what is a stake here is the conceptual correctness
>> >>of the filter. (we can fix the Doxygen documentation accordingly).
>> >>
>> >>
>> >>
>> >>Since the filter is integrating an image across one dimension,
>> >>it is equivalent to computing the integral of a function of
>> >>N-variables along a range of one of those N variables.
>> >>
>> >>
>> >>Something like:
>> >>
>> >>
>> >>          Sum{ F(x,y,z) }    from Z=-inf to Z=inf
>> >>
>> >>
>> >>which we would expect to become a function of the remaining
>> >>variables,
>> >>
>> >>
>> >>something like
>> >>
>> >>
>> >>          G(x,y).
>> >>
>> >>
>> >>If you take a CT scan and integrate the values along the Z
>> >>direction, conceptually this is close to generating a DRR
>> >>(an X-Ray) of that 3D CT image, and therefore it seems
>> >>reasonable to expect that output image to be a 2D image.
>> >>
>> >>
>> >>Expecting the integral of a 3D function to be a 3D degenerate
>> >>function (a 3D image of 1 slice) is a dangerous approach, because
>> >>then filters that are applied to the accumulated image will
>> >>assume that is a 3D image. For example a gradient will not work
>> >>properly on the accumulated image.
>> >>
>> >>
>> >>
>> >>I don't see any difficulty on writing the code for a (N) to (N-1)
>> >>dimensional image. We only need a linear iterator, and a while loop.
>> >>The GenerateData method shouldn't require more than 50 lines of code.
>> >>
>> >>
>> >>
>> >>Have you used this filter ?
>> >>
>> >>
>> >>Could you post some of the cases for which you use this filter ?
>> >>
>> >>
>> >>
>> >>That could help us to understand if the output should be a
>> >>N-dimensional or an (N-1)-dimensional image.
>> >>
>> >>
>> >>
>> >>    Please let us know,
>> >>
>> >>
>> >>
>> >>        Thanks
>> >>
>> >>
>> >>
>> >>           Luis
>> >>
>> >>
>> >>
>> >>--------------------
>> >>Gaetan Lehmann wrote:
>> >>> Hi,
>> >>>
>> >>> The check is correct. The output is an image of the same dimension  
>> to
>> >>keep the
>> >>> info of the output image on the same dimension (the docstring is
>> >>surely
>> >>a lot
>> >>> more clear than me).
>> >>> I don't think it will work if you try to build it with a dim=3 in
>> >>input
>> >>and
>> >>> dim=2 in output.
>> >>> It would be nice to be able to set the dim=3 or dim=2 in output, but
>> >>the
>> >>code
>> >>> will surely be difficult to write.
>> >>>
>> >>> Gaetan
>> >>>
>> >>>
>> >>> On Wednesday 01 March 2006 21:04, Amy Squillacote wrote:
>> >>>
>> >>>>Hi all,
>> >>>>
>> >>>>There is currently a check in the header file of the
>> >>>>AccumulateImageFilter (in Code/BasicFilters) for whether the input
>> >>>>and output images have the same dimension.  Another ITK developer
>> >>>>pointed out to me a couple days ago that this concept check is
>> >>>>probably wrong.  He suggested that the dimension of the output  
>> should
>> >>>>actually be one less than that of the input.  Luis and I discussed
>> >>>>this earlier today, and we believe that the output's dimension  
>> should
>> >>>>be one less than that of the input.  However, if we make this  
>> change,
>> >>>>anyone's code depending on the input and output to have the same
>> >>>>dimensionality would break.
>> >>>>
>> >>>>What has been the experience of other people using this filter?   
>> What
>> >>>>is your opinion about the dimensionality of the input and output of
>> >>>>this filter?
>> >>>>
>> >>>>- Amy
>> >>>>
>> >>>>_______________________________________________
>> >>>>Insight-users mailing list
>> >>>>Insight-users at itk.org
>> >>>>http://www.itk.org/mailman/listinfo/insight-users
>> >>>>
>> >>>>
>> >>>>------------------------------------------------------------------------
>> >>>>
>> >>>>_______________________________________________
>> >>>>Insight-users mailing list
>> >>>>Insight-users at itk.org
>> >>>>http://www.itk.org/mailman/listinfo/insight-users
>> >>
>> >>_______________________________________________
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>> >>http://www.itk.org/mailman/listinfo/insight-developers
>> >>
>>
>>
>>
>> --
>> Gaëtan Lehmann
>> Biologie du Développement et de la Reproduction
>> INRA de Jouy-en-Josas (France)
>> tel: +33 1 34 65 29 66    fax: 01 34 65 29 09
>> http://voxel.jouy.inra.fr
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-- 
Gaëtan Lehmann
Biologie du Développement et de la Reproduction
INRA de Jouy-en-Josas (France)
tel: +33 1 34 65 29 66    fax: 01 34 65 29 09
http://voxel.jouy.inra.fr

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