[vtkusers] Missing update extent request in vtkExtractVOI?

[David Gobbi]

For resampling images, there's also vtkImageResize, which
is much faster if you need to interpolate while resampling:
http://www.vtk.org/Wiki/VTK/Examples/Cxx/Images/ResizeImage

It provides three choices for choosing the output sampling:
1) SetResizeMethodToOutputSpacing() allows you directly select
the sample spacing (in physical units)
2) SetResizeMethodToMagnificationFactors() allows you to select
a factor by which to resample
3) SetResizeMethodToOutputDimensions() allows you to choose
the size of the output grid

The main advantage of this filter is that it is O(n) with respect to the
interpolation kernel size, whereas vtkImageResample is O(n^3).  Of
course, for nearest-neighbor interpolation (e.g. decimation) it makes
no difference, but for sinc interpolation (n=6 or higher) it makes a huge
difference.

For completeness, there is also vtkImageShrink3D for simple image
decimation.

 - David

On Thu, Nov 13, 2014 at 9:58 AM, Berk Geveci <berk.geveci at kitware.com>
wrote:

> We are still working on this.
>
> Meanwhile, you can use vtkImageResample.
>
> Best,
> -berk
>
> On Wed, Nov 12, 2014 at 11:01 AM, Karsten Tausche <
> karsten.tausche at student.hpi.uni-potsdam.de> wrote:
>
>>  Hi,
>>
>> any news about that topic?
>> I need to change the sampling rate of an image dynamically. Are there any
>> other ways to achieve this?
>>
>> Best regards,
>> Karsten
>>
>>
>> On 2014-10-13 16:16, Berk Geveci wrote:
>>
>> We completely rewrote vtkExtractVOI a few months ago and it doesn't look
>> like we didn't do a great job in fully evaluating it. I will spend some
>> quality time with it in the next few weeks.
>>
>>  Best,
>> -berk
>>
>> On Sun, Oct 12, 2014 at 2:06 PM, Karsten Tausche <
>> karsten.tausche at student.hpi.uni-potsdam.de> wrote:
>>
>>>  I just realized that calling SetUpdateExtentToWholeExtent() on a
>>> downstream algorithm (polyData in the example code) "fixes" this error.
>>>
>>>
>>> On 2014-10-11 14:10, Karsten Tausche wrote:
>>>
>>>  Hi everyone,
>>>
>>> I tried to use vtkExtractVOI to decrease the resolution of a
>>> vtkImageData/vtkStructuredPoints data set. This works fine when I set the
>>> sample rate before I connect the filter to the pipeline. But changing the
>>> sample rate while rendering always results in an error like this:
>>>
>>> "ERROR: In
>>> ..\..\..\Common\ExecutionModel\vtkStreamingDemandDrivenPipeline.cxx, line
>>> 857
>>> vtkCompositeDataPipeline (0000000005D6E1A0): The update extent specified
>>> in the information for output port 0 on algorithm
>>> vtkExtractVOI(0000000005D92710) is 0 10 0 10 0 0, which is outside the
>>> whole extent 0 9 0 10 0 0."
>>>
>>> This behavior also depends on the initial sample rate. With the defaults
>>> (1, 1, 1), the error message pops up after changing the rate, and the
>>> filter seems produce the expected result. When I set different initial
>>> values and increase them while rendering, I get the error message above,
>>> but the filter result seems correct. When decreasing the sample rate, I
>>> don't get an error, but the filter decreases the size of the rendered
>>> image.
>>>
>>> I'm using the current VTK master. I appended a small example the
>>> produces this error; it doesn't render any visible points but I didn't know
>>> how to enforce the required updates without adding the filter to a
>>> rendering pipeline.
>>>
>>> BTW the error also occurs with vtkStructuredGrid+vtkExtractGrid.
>>>
>>> Thanks,
>>> Karsten
>>>
>>>
>>>
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>>
>>
>
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