[Insight-users] ImageRandomNonRepeatingConstIteratorWithIndex repeatability

[Luis Ibanez]

Hi Julien,

Thanks for your detailed email.

It looks like you actually found a bug.


Please do the following:

File a bug report at
http://public.kitware.com/Bug/my_view_page.php

and attach to the bug report the code that
you have for reproducing the problem.


If you are interested,
you can also sign up for the:

                 "Adopt-a-Bug"

program
http://www.itk.org/Wiki/ITK_Adopt_a_Bug_Program

and you will get  CVS write access to ITK.
(along with full developer status).


In this way you can commit the fix directly.


The main concern at this point will be to run a full
experimental build with your modification in order
to verify that the proposed fix doesn't break anything
else.

Are you familiar with the process for running an
Experimental build ?

What is your development platform ?
(Windows/Linux/Mac)  ?


    Please let us know,


          Thanks


               Luis



--------------------------------------------------------------------------------------
On Thu, Mar 18, 2010 at 10:05 AM, Julien Malik <julien.malik at c-s.fr> wrote:
> Hello,
>
> I'm experiencing a problem with
> itk::ImageRandomNonRepeatingConstIteratorWithIndex.
>
> I need the following feature :
> [1] iterate on an image by choosing randomly and uniformly a subset of
> pixels of predefined size.
> [2] later, i need to iterate on other images (of the same size of course)
> and iterate on the same set of pixels chosen by the previous walk, in the
> same order : basically, i need to 'replay' the iterations done in [1]
>
> I found itk::ImageRandomNonRepeatingConstIteratorWithIndex to be a very
> elegant solution to my problem.
> For [1], no problem : this is exactly what it does (using SetNumberOfSamples
> to iterate only on a fraction of the image).
> For [2], using ReinitializeSeed(int) with the same seed as in [1] seems to
> be the way to go. With that, I only need to save the seed to be able to
> regenerate the same iterations.
>
> Now the problems :
> * [BUG] when i use
> itk::ImageRandomNonRepeatingConstIteratorWithIndex::ReinitializeSeed(int)
> with the same seed in [1] and [2], i don't get the same set of pixels
> selected.
> I found that modifying RandomPermutation::ReinitializeSeed(int) from
> "m_Generator->Initialize(seed);"
> to
> "m_Generator->SetSeed(seed);"
> solves my problem. It seems there is some kind of buffered data in the
> MersenneTwisterGenerator, and SetSeed calls Initialize + a reload() method
> that must clear those buffered data.
>
> * [Feature Request] the constructor of
> ImageRandomNonRepeatingConstIteratorWithIndex creates a permutation
> internally so that the iterator is ready to walk the image. Calling
> ReinitializeSeed recreate the permutation, involving the generation of a
> random number for each pixel in the region + a std::sort of all these random
> numbers.
> For performance, it would be nice to have an additionnal constructor where
> the seed can be explicitely specified.
>
>
> Can you confirm the bug ? Or am I doing something wrong ?
> If needed, I can provide code demonstrating the non-repeatability of the
> iterator.
>
>
> Regards,
> Julien
>
> _____________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
>
> Kitware offers ITK Training Courses, for more information visit:
> http://www.kitware.com/products/protraining.html
>
> Please keep messages on-topic and check the ITK FAQ at:
> http://www.itk.org/Wiki/ITK_FAQ
>
> Follow this link to subscribe/unsubscribe:
> http://www.itk.org/mailman/listinfo/insight-users
>