Cannot apply any filter

I imported segmentation file from itk-SNAP in vtk format in Paraview(ver 5.9.1).
Every filter looks in gray and is not applicable to my model

Also when I put the cursor on contour filter icon, ‘Requires an input’ message shows.

How can it be fixed? Specifically I want to apply contour filter to my model.
Is it the problem of my file?

Thank you in advance.

Press apply.


Thanks so much :sweat_smile: :slight_smile: