[Insight-developers] iterator without index efficiency problem

[Miller, James V (GE, Research)]

Gaetan, 

I was just looking through the projection code. It looks like the code is iterating
over regions which are one pixel wide/tall/deep depending on the projection direction.
Do you have a sense for whether the timings of the iterators are different for all the projection directions?

The overhead in the ImageRegionIterator is in the wrapping from row to 
row in the region.  For long rows, the overhead is essentially amortorized,
adding little overhead to each pixel. But if the region is only walking a 
row of length 1, the overhead of row wrapping is applied to very pixel.

Jim



-----Original Message-----
From: insight-developers-bounces+millerjv=crd.ge.com at itk.org
[mailto:insight-developers-bounces+millerjv=crd.ge.com at itk.org]On Behalf
Of Gaetan Lehmann
Sent: Monday, February 20, 2006 10:22 AM
To: Miller, James V (GE, Research); insight-developers at itk.org
Subject: Re: [Insight-developers] iterator without index efficiency
problem



I forgot to say that the timing test should be run with the command line

./perf ../images/ESCells.img

and that the result were very similar before switching to iterator with  
index.

Gaetan

On Mon, 20 Feb 2006 15:16:07 +0100, Miller, James V (GE, Research)  
<millerjv at crd.ge.com> wrote:

> Gaetan,
>
> Where are your timing comparisons between the iterator types?
>
> We have studied the performance of the iterators several times.  The last
> in depth study was a several years ago.  Maybe something has changed.
>
> In previous studies, we ran both sets of iterators over a common task.
> While the program did report a difference in iterator timings, if we
> switched which iterator performed the task first, the timings would
> flip, leading to a different conclusion.
>
> To accumulate over different dimensions, you might want to consider the
> ImageLinearConstIteratorWithIndex.  Depending on how you are accumulating
> the information along a direction, this iterator may be more effecient  
> than
> a ImageRegionIterator or a ImageRegionIteratorWithIndex.
>
> I'll out together a test on the iterator performance so that we can
> benchmark the iterators.
>
> Jim
>
> -----Original Message-----
> From: insight-developers-bounces+millerjv=crd.ge.com at itk.org
> [mailto:insight-developers-bounces+millerjv=crd.ge.com at itk.org]On Behalf
> Of Gaetan Lehmann
> Sent: Monday, February 20, 2006 7:57 AM
> To: insight-developers at itk.org
> Subject: [Insight-developers] iterator without index efficiency problem
>
>
>
> Hi,
>
> I have noted a huge difference fo efficiency between the iterator with or
> without index: the iterator with index is more efficient than the one
> without index.
> Is it a known problem ?
> I'm using ITK2.4.1. Is is still valid in ITK cvs ? If yes, it should be
> fixed before the 2.6 release.
> I have noticed that while working of projections. Timing test can be ran
> to reproduce that.
> http://insight-journal.org/view_reviews.php?back=index.php&pubid=71
>
> Reagards,
>
> Gaetan
>



-- 
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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