[vtkusers] How to understand the slab thickness, slab resolution, spacing

[David Gobbi]

Hi Zhang,

The code for vtkImageSlabReslice shows what SlabThickness and
SlabResolution do:

https://gitlab.kitware.com/vtk/vtk/blob/master/Imaging/
General/vtkImageSlabReslice.cxx#L47

  this->NumBlendSamplePoints = 2*(static_cast<
      int >(this->SlabThickness/(2.0 * this->SlabResolution))) + 1;
  this->SlabNumberOfSlices = this->NumBlendSamplePoints;

and:

  spacing[2] = this->SlabResolution;

The SlabThickness is only used to compute the SlabNumberOfSlices (which is
an integer).  And the SlabResolution overrides the slice spacing.  The
vtkImageSlabReslice filter is not meant to be used as a 3D output filter.

The output slice thickness is always an integer multiple of the output
slice spacing.  This can be tweaked a little with the TrapezoidIntegration
option, but a true fractional slice thickness isn't possible.
http://www.vtk.org/doc/nightly/html/classvtkImageReslice.html#
a9a8fb0ce5f767733bbce72f5be32b409
https://en.wikipedia.org/wiki/Trapezoidal_rule

A different way to reduce image noise when reslicing is to use
vtkImageSincInterpolator with SetBlurFactors:
http://www.vtk.org/doc/nightly/html/classvtkImageSincInterpolator.html#
aa662697dec4b11dacfc21e062fb1551f
but the result will be different from thick slicing.

 - David


On Sat, Jul 29, 2017 at 3:06 AM, zhang qiang <zhang07101 at 126.com> wrote:

> Dear David:
>
>     Sorry for not CC to vtkusers list.
>
>     For vtkImageReslice, if the output spacing[2] = 0.4, I can set the
> thickness of resliced image to 0.4*n by set the SetSlabNumberOfSlices to n.
> If I want the thickness to be 1mm, n will be 2.5. But the type of n is int,
> so n can not be 2.5, which means the thickness can not be 1mm if the
> outputspacing[2]=0.4. Am I right?
>
>     On the other hand, I still feel confused about the vtkImageSlabReslice.
> What's the meaning of slab resolution and slab thickness? And after set the
> output spacing to (0.4,0.4,0.4), why the reslicedSpacing[2] of resliced
> image was not 0.4?
>
>         vtkSmartPointer<vtkImageSlabReslice> resliceFilter =
> vtkSmartPointer<vtkImageSlabReslice>::New();
>         resliceFilter->SetInputData(originalData);
>         resliceFilter->SetOutputSpacing(0.4,0.4,0.4);
>         resliceFilter->SetInterpolationModeToLinear();
>         resliceFilter->SetOutputDimensionality(3);
>         resliceFilter->Update();
>
>         double reslicedSpacing[3];
>         reslicedData->GetSpacing(reslicedSpacing);
>
>      Best wishes!
> zhang qiang
>
>
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