[Insight-users] Problems with image corruption : Reusing filters

[Radhika Sivaramakrishna]

Hi Luis and Jim,
Thanks for clarifying how the pipeline works. The explanation was very
useful.
Radhika

----- Original Message ----- 
From: "Luis Ibanez" <luis . ibanez at kitware . com>
To: "Radhika Sivaramakrishna" <radshashi at earthlink . net>
Cc: <insight-users at itk . org>
Sent: Wednesday, December 17, 2003 8:17 PM
Subject: Re: [Insight-users] Problems with image corruption : Reusing
filters


>
> Hi Radhika,
>
>   - Code reuse is a good thing
>   - Variable names reuse is a bad, very bad thing
>
>   - Filter reconection is a dangerous practice
>
> Nothing good can result from saving a couple of bytes
> in one extra pointer in your program.
>
> When you reused "extracter2D" you were probably
> thinking in terms of procedural programming.  e.g.
> invoking functions for performing processing on data.
>
> The data flow pipeline is a different paradigm.
> It is like connecting circuits: When you need a
> second switch, you don't take it out from somewhere
> else in the circuit... you just add a new one  :-)
>
> When you connect the filter with
>
>          a->SetInput( b->GetOutput() )
>
> Those connections are intended to be used in a
> permanent way by running data through the filters
> multiple times.
>
> If you need a second extract filter, you should
> (as you discovered by yourself) create a new extract
> filter object and connect it in the pipeline in the
> new appropriate place.
>
> It is a "pipeline": you put the tubes, the elbows,
> the tees, the valves,... as many as you need, and
> once you install them, you don't take them out.
> Especially not just before letting water run through
> the pipe.
>
>
> Think "plumber" and you will be ITK-enlightened.
>
>
>
> Regards,
>
>
>     Luis
>
>
> --------------------------------
> Radhika Sivaramakrishna wrote:
>
> > Hi Luis,
> > Thanks for your suggestion. I will try this also, but I am not sure if
this
> > is the problem though it is a good suggestion. After I sent off that
piece
> > of code to you, I decided to do some more experimenting. In the code I
sent
> > you I reused extracter2D (ExtractImageFilter Pointer) twice once to
extract
> > a slice from the greyscale image, and then a second time to extract a
slice
> > off the mask image. I decided to use two different pointers (one
> > extracter2Dimage and another extracter2Dmask) and lo and behold, things
> > started working and things were written out correctly. I dont understand
why
> > this should happen? Could you explain?
> >
> > Radhika
> >
> >
> > ----- Original Message ----- 
> > From: "Luis Ibanez" <luis . ibanez at kitware . com>
> > To: "Radhika Sivaramakrishna" <radshashi at earthlink . net>
> > Cc: <insight-users at itk . org>
> > Sent: Wednesday, December 17, 2003 11:19 AM
> > Subject: Re: [Insight-users] Problems with image corruption : Shouldn't
use
> > LargestPossibleRegion for Iterators.
> >
> >
> >
> >>Hi Radhika,
> >>
> >>It seems that the error is related to the use of
> >>"GetLargestPossibleRegion()" in order to define
> >>the iterators in line 230 of your code:
> >>
> >>
> >>
> >>>    ImageType2D::RegionType region =
binimg->GetLargestPossibleRegion();
> >>>    ConstIteratorType maskit (mask, region);
> >>>    ConstIteratorType binimgit( binimg, region );
> >>>    IteratorType newmaskit(newmask,region);
> >>>
> >>>   maskit.GoToBegin();
> >>>   binimgit.GoToBegin();
> >>>   newmaskit.GoToBegin();
> >>>   while( ! maskit.IsAtEnd() && ! binimgit.IsAtEnd() && !
> >
> > newmaskit.IsAtEnd())
> >
> >>>     {
> >>>newmaskit.Set(binimgit.Get());
> >>>       if( maskit.Get() == 0 )   // if mask pixel is off
> >>>         {
> >>>newmaskit.Set(0);
> >>>         }
> >>>       ++maskit;
> >>>++binimgit;
> >>>++newmaskit;
> >>>     }
> >>
> >>In general you shouldn't use "LargestPossibleRegion"
> >>since there is no guarranty that all this data is
> >>going to be in memory.  The safe region to use is the
> >>"Buffered" region.
> >>
> >>Just to make sure that this is the problem, please
> >>insert the line:
> >>
> >>            binimg->Print( std::cout )
> >>
> >>in line 229, run the program and look at the printed
> >>values of the image regions. There will be: Requested,
> >>Buffered and LargestPossible region.
> >>
> >>My guess is that the largest possible region is
> >>larger than the buffered region and your iterators
> >>are stepping out of the image buffers, therefore
> >>corrupting the memory.
> >>
> >>BTW the process that you are attempting with the
> >>iterators is done by the MaskImageFilter
> >>http://www . itk . org/Insight/Doxygen/html/classitk_1_1MaskImageFilter . html
> >>
> >>You may simply replace this while loop with a
> >>MaskImageFilter.
> >>
> >>
> >>
> >>Please let us know what you find.
> >>
> >>
> >>Thanks
> >>
> >>
> >>   Luis
> >>
> >>
> >>
> >>------------------------------------
> >>Radhika Sivaramakrishna wrote:
> >>
> >>>Hi Luis,
> >>>I am having some problems with my program. I have enclosed a portion of
> >>>my code here where the problem is. I am not able to figure it out.
> >>>Basically, "binimg" in my code is the output of the relabel filter. At
> >>>that point when I write it out, it is correct. However, further down
the
> >>>line, when I try to write out the output of the relabel filter, it is
> >>>corrupted. In fact, all are corrupted and they all have the same values
> >>>which is that of the result of the mask filter. Even "gs" the output of
> >>>the extractimagefilter is wrong at the point where I am writing it out.
> >>>Could you help me figure out the problem? Maybe there is something
wrong
> >>>in the way I am setting the region of iteration for each or is there a
> >>>problem in reusing the extractimagefilter for first extracting a
> >>>greyscale slice and then using the same thing to extract a mask?
> >>>
> >>>Thanks
> >>>Radhika
> >>>
> >>
> >>
> >>
> >
> >
> >
>
>
>