vtkImagePlaneWidet: control output spacing

Hi all

Does anyone know how to control the output spacing when vtkImagePlane Widget ?
My scenario is this: I have set up a vtkImagePlaneWidget, I bulld the vtkPlaneSource manually from and feed the Origin and Point1 and Point2 to the vtkImagePlaneWidget.
However, because I need the output planar image ( from vtkImagePlaneWidget) to be of a specific resolution, I am not sure how / where to set that.