VTK Screenshot save images different as the visualization in renderer window

I follow the tutorial for screenshot in python: 
https://lorensen.github.io/VTKExamples/site/Python/Utilities/Screenshot/
<https://lorensen.github.io/VTKExamples/site/Python/Utilities/Screenshot/>  

This is the camera view in the renderer window
<http://vtk.1045678.n5.nabble.com/file/t342668/unnamed.png> 

The screen shot suppose to capture this camera view, however the saved png
image is a different view:
<http://vtk.1045678.n5.nabble.com/file/t342668/unnamed-2.png> 

Am I using the right method? Any comment is appreciated




--
Sent from: http://vtk.1045678.n5.nabble.com/VTK-Users-f1224199.html
_______________________________________________
Powered by www.kitware.com

Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html

Please keep messages on-topic and check the VTK FAQ at: http://www.vtk.org/Wiki/VTK_FAQ

Search the list archives at: http://markmail.org/search/?q=vtkusers

Follow this link to subscribe/unsubscribe:
https://vtk.org/mailman/listinfo/vtkusers