[vtkusers] vtkImageReslice question

[David Gobbi]

Hi Andi,

A memory allocation error on a 10MB allocation sounds suspicious.  You
might have to dig deeper to see exactly why the call is failing,
because it probably isn't an actual "out of memory" problem.  If you
run inside a debugger, can you get a stack trace for when the "new"
call fails?

When I'm doing oblique slicing, I usually call UpdateWholeExtent() on
the filter before the reslice (in your case, this is the shiftscale).
This is necessary because, as you have seen, oblique slicing generates
large UpdateExtents that are always changing.  This won't help the
memory issue, but it will make your app run faster.

   David


On Fri, Dec 18, 2009 at 4:29 AM, Andi2008 <mail-andi at web.de> wrote:
>
> Hi,
>
> thank you for the answer. I use one vtkImageReslice for one single view and
> i extract always a single slice. I agree with you that the output extent of
> axial/sagittal and coronal views is always the same and I checked my code
> for this and found out my program doesnt crashes when I just display the
> three orthogonal views.
> But I implemented also the ablility to reslice in any possible direction and
> angles. In this case it happens what you descibe. In every time Render is
> called the outputextent is recalculated because it is always different. I
> implemented the pipeline like:
>
>        m_vtkShiftscale = vtkImageShiftScale::New();
>        m_vtkShiftscale->SetInput(volumedata->getImageData()); //<-- vtkImageData
> with the volume
>        m_vtkShiftscale->SetShift(0.5*m_nWindow - m_nLevel);
>        m_vtkShiftscale->SetScale(255.0/m_nWindow);
>        m_vtkShiftscale->ClampOverflowOn();
>        m_vtkShiftscale->SetOutputScalarTypeToUnsignedChar();
>
>        m_vtkImageReslicer = vtkImageReslice::New();
>        m_vtkImageReslicer->SetInput(m_vtkShiftscale->GetOutput());
>        m_vtkImageReslicer->SetOutputDimensionality(2);
>        m_vtkImageReslicer->SetInterpolationModeToCubic();
>        m_vtkImageReslicer->SetOutputSpacing(spacing);
>        m_vtkImageReslicer->AutoCropOutputOn();
>        m_vtkImageReslicer->Update();
>
> I perform the reslicing by calculating a new transformationmatrix by given
> centerpoint and angles around x,y and z axis. I call the SetResliceAxis
> method to set the new transformationmatrix the call Update to perform the
> reslice. During the update it crashes if there is not enough memory. The
> amount of needed memory is not that much(usually around 10mb) but it can
> happend that it can't be allocated. I know that the outpuextent is not
> exact. Therefore I call the imageshiftscale before the reslice. Otherwise i
> get gray areas in the resultimage in cause of the window/level calculation.
>
> How can I prevent this crash?
> Kind regards
> Andi
>
>
>
>
>
> David Gobbi-3 wrote:
>>
>> Check the WholeExtent of the output from reslice.  By default, the
>> size of the OutputExtent is set to be large enough to fully contain
>> the transformed input Extent.  Try to imagine a rotated cube inside of
>> larger enclosing cube.  The volume of the outer cube can be many times
>> larger than that of the inner cube, especially for rotations of 45
>> degrees.
>>
>> You need to set the OutputExtent of reslice to something reasonable
>> for your application.  Don't rely on the default output extent.  If
>> you are doing the reslicing so that you can view individual slices,
>> then set the output extent to just a single slice.
>>
>> I'm not sure whether you are guilty of this, but I've seen several
>> people who use ImageReslice to rotate the whole volume, and then use
>> VOI or ImageClip or ImageActor to extract slices in the three
>> directions (axial, sagittal, coronal).  This is bad design, because
>> one of two things will happen: 1) on each render, each view requests a
>> different update extent, which forces reslice to re-execute on each
>> and every render. 2) if reslice.UpdateWholeExtent() is called, the
>> unnecessary re-executions don't occur, but a lot of memory is used.
>> The proper way to use reslice is to use one reslice per view
>> orientation.
>>
>>    David
>>
>>
>> On Thu, Dec 17, 2009 at 9:00 AM, Andreas Brüning <mail-andi at web.de> wrote:
>>> Hello,
>>>
>>> ich have a problem when i use vtkImageReslice on a very large volume.
>>> Sometimes when i don't have enough memory for the reslice operation the
>>> global warningwindow appears. In there is written that vtk is unable to
>>> allocate an amount of memory. After this my program crashes immediately
>>> and i would like to catch this before it crashes. Is there a way get a
>>> notification when there is not enough memory? (maybe a callback function)
>>>
>>> Thanks in advance
>>> Andi
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