Is there any way I can get the corresponding image before rendering volume to the window

dear all,
I want to know if VTK provides any method to save the image rendered by vtkSmartVolumeMapper. I know vtkWindowToImageFilter, but its implementation requires rendering data to the window,the effect is similar to screenshots. Is there any way can be directly exported to vtkimagedata, or a similar data format,without randering data to window?

The feature that you are looking for is called “off-screen rendering”. VTK supports this. Google search for this keyword should help you getting started.