# VTK9 create different stencil than vtk8
**URL:** https://discourse.vtk.org/t/vtk9-create-different-stencil-than-vtk8/10560
**Category:** Support
**Created:** [January 30, 2023, 2:12pm UTC](https://discourse.vtk.org/t/vtk9-create-different-stencil-than-vtk8/10560 "2023-01-30T14:12:46Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@lucas\_rouhier](https://discourse.vtk.org/u/lucas_rouhier)
#### Post date: [January 30, 2023, 2:12pm UTC](https://discourse.vtk.org/t/vtk9-create-different-stencil-than-vtk8/10560/1 "2023-01-30T14:12:46Z")
Hello,
I am having some weird results while trying to update my VTK.
I am converting a VTK polydata to Image data with the following code:
vtkSmartPointer VtkPolyDataToImage(vtkPolyData\* poly, vtkImageData\* templateImage)
{
vtkSmartPointer image = vtkSmartPointer::New();
image-\>DeepCopy(templateImage);
// fill the image with foreground voxels:
short inval = 1;
short outval = 0;
vtkIdType count = templateImage-\>GetNumberOfPoints();
for (vtkIdType i = 0; i \< count; ++i)
{
image-\>GetPointData()-\>GetScalars()-\>SetTuple1(i, inval);
}
// polygonal data → image stencil:
vtkSmartPointer pol2stenc =
vtkSmartPointer::New();
pol2stenc-\>SetInputData(poly);
pol2stenc-\>SetOutputOrigin(image-\>GetOrigin());
pol2stenc-\>SetOutputSpacing(image-\>GetSpacing());
pol2stenc-\>SetOutputWholeExtent(image-\>GetExtent());
pol2stenc-\>Update();
// cut the corresponding white image and set the background:
vtkSmartPointer imgstenc = vtkSmartPointer::New();
imgstenc-\>SetInputData(image);
imgstenc-\>SetStencilConnection(pol2stenc-\>GetOutputPort());
imgstenc-\>ReverseStencilOff();
imgstenc-\>SetBackgroundValue(outval);
imgstenc-\>Update();
vtkSmartPointer outputImage = imgstenc-\>GetOutput();
return outputImage;
}
However, After upgrading the created image is different (like 0.2 max difference).
Do you have any idea about what could the issue here ? Is it a known issue ?
Thanks in advance
---
### Author:  [@dgobbi](https://discourse.vtk.org/u/dgobbi)
#### Post date: [January 30, 2023, 4:06pm UTC](https://discourse.vtk.org/t/vtk9-create-different-stencil-than-vtk8/10560/2 "2023-01-30T16:06:57Z")
Can you explain what you mean by “0.2 max difference”? I don’t understad what the “0.2” refers to.
The vtkPolyDataToImageStencil class has only been stylistically modified between VTK 8.2.0 and VTK 9.2.5. The algorithm hasn’t changed.
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### Author:  [@lucas\_rouhier](https://discourse.vtk.org/u/lucas_rouhier)
#### Post date: [January 30, 2023, 4:35pm UTC](https://discourse.vtk.org/t/vtk9-create-different-stencil-than-vtk8/10560/3 "2023-01-30T16:35:45Z")
Sure ! I remeshed the image back to an STL and computed the difference between the 2 meshes (vtk 8 one and vtk9 one) (point by point euclidean distance). That is what gave me the 0.2 difference.
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### Author:  [@dgobbi](https://discourse.vtk.org/u/dgobbi)
#### Post date: [January 30, 2023, 4:42pm UTC](https://discourse.vtk.org/t/vtk9-create-different-stencil-than-vtk8/10560/4 "2023-01-30T16:42:16Z")
You weren’t directly comparing the images to each other? What did you use to do the remeshing? And what was the voxel spacing?
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### Author:  [@lucas\_rouhier](https://discourse.vtk.org/u/lucas_rouhier)
#### Post date: [January 30, 2023, 4:49pm UTC](https://discourse.vtk.org/t/vtk9-create-different-stencil-than-vtk8/10560/5 "2023-01-30T16:49:37Z")
No I did not because I first saw the error on remeshed STL’s and I did not think about the meshing part… Which will also be impacted by that vtk9 → vtk9 upgrade
here is the code used to remesh the image : [Meshing code text code | WTOOLS](https://wtools.io/paste-code/bJpp) (using marching cube)
Voxel spacing is 0.15
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### Author:  [@dgobbi](https://discourse.vtk.org/u/dgobbi)
#### Post date: [January 30, 2023, 4:57pm UTC](https://discourse.vtk.org/t/vtk9-create-different-stencil-than-vtk8/10560/6 "2023-01-30T16:57:44Z")
The vtkQuadricDecimation filter has definitely been changed since VTK 8.2.
To check vtkPolyDataToImageStencil, please do a voxel-by-voxel comparison of the image outputs. Or if that isn’t possible, then compare the vtkMarchingCubes meshes without decimating them first.
---
### Author:  [@lucas\_rouhier](https://discourse.vtk.org/u/lucas_rouhier)
#### Post date: [January 30, 2023, 5:01pm UTC](https://discourse.vtk.org/t/vtk9-create-different-stencil-than-vtk8/10560/7 "2023-01-30T17:01:45Z")
Perfect thanks a lot for your help ! Hopefully that will provide some new information and perhaps a solution.