[ITK-dev] regarding ImageFileReader::GenerateOutputInformation()

[Rashad M]

Hello Brad,

Thanks for your reply. I had check the UpdateOutputInformation() with a
seperate test code and there was no problem. I found that there are
multiple instances of Reader created in every execution of the my code
which was the cause of the error/behaviour I was having.

On Thu, Aug 13, 2015 at 9:11 PM, Bradley Lowekamp <blowekamp at mail.nih.gov>
wrote:

> Hello Rashad,
>
> If you call ImageFileReader::UpdateOutputInformation() 2 times is "should"
> only call GenerateOutputInformation once.
>
> The key to this behavior is the management of the timestamps in the
> process object classes done here [1].
>
> What is required for this to work correctly is that the only the correct
> object get modified in these pipeline methods. When an object is modified
> the timestamp should be updated, and downstream processes get marked as out
> of date.
>
> The best way to make sure your ImageSource does not get call twice is to
> write a test, that makes sure the process object's MTime does not change in
> GenerateOutputInformation call.
>
> HTH,
> Brad
>
> [1]
> https://github.com/InsightSoftwareConsortium/ITK/blob/9f88e4e3b388ee2f1c1c006ae36de0613d305284/Modules/Core/Common/src/itkProcessObject.cxx#L1431-L1542
>
> On Aug 13, 2015, at 2:55 PM, Rashad M <mohammedrashadkm at gmail.com> wrote:
>
> Hello all,
>
> The documentation of   itk::ProcessObject::GenerateOutputInformation( )
>  says
> Generate the information describing the output data. [1]. The GenerateOutputInformation()
> in itkImageFileReader first create all instances of ImageIO and setup
> direction, spacing, etc..
>
> If I understand correctly, the GenerateOutputInformation in the image file
> reader is  called by UpdateOutputInformation( )
>
> To my question,
> If I call reader->UpdateOutputInformation() for first time it calls
> reader->GenerateOutputInformation() as described in docs[2].
>
> Now If I have a second call to reader->UpdateOutputInformation( ) ?
>
> Will it again go to GenerateOutputInformation() and createAllInstances of
> imageio , do the same thing again!
>
> In itkProcessObject.cxx, there is the below documentation
>
>    * Call GenerateOutputInformation for subclass specific information.
>    * Since UpdateOutputInformation propagates all the way up the pipeline,
>    * we need to be careful here to call GenerateOutputInformation only if
>    * necessary. Otherwise, we may cause this source to be modified which
>    * will cause it to execute again on the next update.
>
> How can I prevent it from calling it again in class sub class of
> itk::ImageSource?
>
> [1]
> http://www.itk.org/Doxygen/html/classitk_1_1ProcessObject.html#abe61fb6b7de8c443e7af1561bd722736
>
>
> --
> Regards,
>    Rashad
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-- 
Regards,
   Rashad
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