[vtkusers] vtkImageThreshold and vtkContourFilter Resolution

[Bill Lorensen]

ContourFIlter does sub voxel interpolation. ThresholdFIiter makes a binary
decision about whether a voxel is inside or outside the surface. Running
ContourFilter on a Thresholded image defeats the purpose of the sub voxel
interpolation.

If you have a more complex segmentation algorithm where you are assigning
integral labels for a number of different classes, then you should run
DiscreteMarchingCubes, since you can't interpolate between arbitrary
integral labels. But you will not get a smooth isosurface. Depending on your
application, you may need to smooth the polydata.

This example illustrate DiscreteMarchingCubes:
http://vtk.org/Wiki/VTK/Examples/Medical/GenerateModelsFromLabels

Bill

On Wed, Jul 28, 2010 at 10:05 AM, Paulo Henrique Junqueira Amorim <
paulojamorim at gmail.com> wrote:

> Hi,
>
> I'm using vtkImageThreshold to segment an image and to generate
> vtkContourFilter to generate the vtkPolyData, but the resolution of
> vtkPolyData not getting good by comparison when it is used only the
> vtkContourFilter to generate vtkPolyData (attached screens).
>
> *Part of the code vtkImageThreshold and vtkContourFilter*
>
> t = vtk.vtkImageThreshold()
> t.SetInput(reader.GetOutput())
> t.ThresholdBetween(226,3021)
> t.SetOutValue(-1024)
> t.Update()
>
> contour = vtk.vtkContourFilter()
> contour.SetInput(t.GetOutput())
> contour.SetValue(0, 226) # Initial threshold
> contour.SetValue(1, 3021) # final threshold
> contour.ComputeScalarsOn()
> contour.ComputeGradientsOn()
>
> [image: vtkImageThreshold.PNG]
>
> *
>
>
>
> Part of the code only vtkContourFilter*
>
> contour = vtk.vtkContourFilter()
> contour.SetInput(reader.GetOutput())
> contour.SetValue(0, 226) # Initial threshold
> contour.SetValue(1, 3021) # final threshold
> contour.ComputeScalarsOn()
> contour.ComputeGradientsOn()
>
>
> [image: vtkContourFilter.PNG]
>
>
>
> Is it possible to use the vtkImageThreshold and vtkContourFilter but the
> end result be equal to use only vtkContourFilter to generate polydata ??
>
>
>
> Regards,
> Paulo Amorim
>
>
>
>
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