::New();
stencil->SetStencilData(poly2Stencil->GetOutput());
stencil->SetInputData(m_OriginalImage);
stencil->ReverseStencilOff();
double ranges[2];
m_OriginalImage->GetScalarRange(ranges);
stencil->SetBackgroundValue(ranges[0]);
stencil->Update();
m_BoneReductionImage = stencil->GetOutput();
```
Here is the code. I created a vtkCylinderSource, which is used as the input of the vtkPolyDataToImageStencil. In this block, it works well. But if I change “poly2Stencil-\>SetInputConnection(cy-\>GetOutputPort());” to “poly2Stencil-\>SetInputData(cy-\>GetOutput());”. This will not work.
Anyone knows how to understand this?
---
### Author:  [@dgobbi](https://discourse.vtk.org/u/dgobbi)
#### Post date: [August 26, 2021, 2:36pm UTC](https://discourse.vtk.org/t/vtkpolydatatoimagestencil-issue/6475/2 "2021-08-26T14:36:18Z")
To use `cy->GetOutput()`, you must call `Update()` beforehand:
```auto
cy->Update();
```
With `SetInputConnection()` the upstream update is automatic. But with `SetInputData()`, you must do the upstream update yourself. That’s the main difference between `SetInputConnection()` and `SetInputData()`.
---
### Author:  [@Hanxin\_Hua](https://discourse.vtk.org/u/Hanxin_Hua)
#### Post date: [August 26, 2021, 2:55pm UTC](https://discourse.vtk.org/t/vtkpolydatatoimagestencil-issue/6475/3 "2021-08-26T14:55:13Z")
Thank you so much for the fast reply and it works well!
So, the thing is I’m building my own polydata for the input. Here’s the code. I thought it was the polydata thing that makes this not work. But maybe I still miss some update call here?
```
vtkSmartPointer points = vtkSmartPointer::New();
double origin[3];
m_OriginalImage->GetOrigin(origin);
double offsetx[14] = { 0, 5, 10, 15, 15, 10, 5, 0, -5, -10, -15, -15, -10, -5 };
double offsety[14] = { 0, 5, 10, 15, 25, 20, 15, 10, 15, 20, 25, 15, 10 ,5 };
for (int i = 0; i < 14; ++i) {
points->InsertNextPoint(origin[0] + offsetx[i], origin[1] + offsety[i], origin[2]);
}
for (int i = 0; i < 14; ++i) {
points->InsertNextPoint(origin[0] + offsetx[i], origin[1] + offsety[i], origin[2] + 20);
}
// Generate the polygon poly data
vtkIdType numPoints = points->GetNumberOfPoints();
vtkSmartPointer polygons = vtkSmartPointer::New();
vtkSmartPointer boundaryPolygon1 = vtkSmartPointer::New();
vtkSmartPointer boundaryPolygon2 = vtkSmartPointer::New();
int oneSidePointsNum = numPoints / 2;
boundaryPolygon1->GetPointIds()->SetNumberOfIds(oneSidePointsNum);
boundaryPolygon2->GetPointIds()->SetNumberOfIds(oneSidePointsNum);
for (vtkIdType i = 0; i < oneSidePointsNum; i++) {
boundaryPolygon1->GetPointIds()->SetId(i, i);
boundaryPolygon2->GetPointIds()->SetId(i, i + oneSidePointsNum);
}
polygons->InsertNextCell(boundaryPolygon1);
polygons->InsertNextCell(boundaryPolygon2);
for (vtkIdType i = 0; i < oneSidePointsNum; i++) {
vtkIdType ids[4] = { i, (i + 1) % 14, (i + 1) % 14 + 14, i + 14 };
polygons->InsertNextCell(4, ids);
}
polygons->Modified();
// Create a PolyData
vtkSmartPointer polygonPolyData = vtkSmartPointer::New();
polygonPolyData->SetPoints(points);
polygonPolyData->SetPolys(polygons);
polygonPolyData->Modified();
// Generate the stencil according to the poly data
vtkSmartPointer poly2Stencil = vtkSmartPointer::New();
poly2Stencil->SetInputData(polygonPolyData);
```
The rest is the same
---
### Author:  [@dgobbi](https://discourse.vtk.org/u/dgobbi)
#### Post date: [August 26, 2021, 3:15pm UTC](https://discourse.vtk.org/t/vtkpolydatatoimagestencil-issue/6475/4 "2021-08-26T15:15:53Z")
If you build your own polydata, then the Update() is not needed. When you run this code, does it give an error message, or does it do nothing?
You can check your polydata by writing a short test program that displays it (with vtkPolyDataMapper and vtkActor). Another useful check is vtkOutlineFilter, it will generate a polydata cube around your image, so that you can compare to the polydata that you built by hand.
---
### Author:  [@Hanxin\_Hua](https://discourse.vtk.org/u/Hanxin_Hua)
#### Post date: [August 26, 2021, 3:27pm UTC](https://discourse.vtk.org/t/vtkpolydatatoimagestencil-issue/6475/5 "2021-08-26T15:27:06Z")
so, in the the first example, I used the cylinder. The image will be cut out of a cylinder, which is desired.
And in this polydata example, the whole image disappears. But there is no error message
I’ll check the vtkOutlineFilter, thank you for your help!