[vtkusers] How to dump images correctly in Python

[David Gobbi]

Hi Willi,

An output exists for as long as its generator exists.  Likewise, the
generator exists for as long as the output exists.  As long as your
program is making use of one or the other, neither will be freed.  So
what you should do is copy the output into a new data object:

o = vtkImageData()
o.DeepCopy(f.GetOutput())

After you do that, you can delete the original output and the entire
pipeline that it was connected to.  The new output (i.e. the copy) can
be used as input to a new pipeline.  You can also try ShallowCopy()
instead of DeepCopy(), but after ShallowCopy the original output and
its copy share the same data array, so after ShallowCopy you should
call ReleaseData on the original output.

By the way, this is not wrapper-specific.  It is exactly the same for
VTK in C++.

 - David

On Tue, Feb 12, 2013 at 5:49 AM, Willi Huber
<surfersparadise85-vtk at yahoo.com> wrote:
> Hello all,
>
> I still have the same problems.
>
> What is the deal with vtk GetOutput(), GetOutputPort() etc.?
> How long does the generator object of this GetOutput() live? Can it be
> dumped right after obtaining GetOutput(). How can it be dumped?
> How long does the GetOutput()-object, e.g. an image, live? How can it make
> it be collected by the garbage collection?
>
> I am generating a large amount of images which have to get dumped correctly.
> Please advice me what to do. I think this advices are also helpful for later
> generations of VTK-wrapper users.
>
> I have also problems generating only a plain image with a certain value.
> What I am currently doing is:
>
> def generate_scalar_value_filled_3d_vtkImageData(spacing, origin, extent,
> scalar_type, scalar_value):
>     import vtk
>
>     image = vtk.vtkImageData()
>     image.SetExtent([0, 0, 0, 0, 0, 0])
>     image.SetOrigin(origin)
>     image.SetSpacing(spacing)
>     image.SetScalarType(scalar_type)
>     image.AllocateScalars()
>
>     padder = vtk.vtkImageConstantPad()
>     padder.SetOutputWholeExtent(extent)
>     padder.SetConstant(scalar_value)
>     padder.SetInput(image)
>     padder.Update()
>
>     out = padder.GetOutput()
>     # image.ReleaseData()
>
>     return out
>
> Whenever I call ReleaseData on the image my output is somewhat influenced. I
> cannot explain in which way. Can somebody explain me all the underlying
> structure and ideas? I am getting more and more confused from minute to
> minute.
>
> Thanks in advance.
>
> Best,
> Willi
>
>
> ________________________________
> Von: Willi Huber <surfersparadise85-vtk at yahoo.com>
> An: "vtkusers at vtk.org" <vtkusers at vtk.org>
> Gesendet: 20:30 Montag, 11.Februar 2013
> Betreff: [vtkusers] How to dump images correctly in Python
>
> Hello all,
>
> I am having serious space problems. With my program I constantly generate
> images and I thought the internal garbage collector of python takes care but
> it doesn't seem so whenever I give an image to an other filter.
> Now I am trying to delete all the unnecessary images by my own. Is there a
> common way to do this? I am using ReleaseData(). Is there a way to see what
> references a certain object?
>
> How is a image in vtk gernerated by a filter? Is it always a new image
> whenever I call GetOutput() or still the same all the time?
>
> Best,