[vtkusers] picture showing with vtkImageShiftScale

[JohnMark]

hi,
when I compiled an example of vtkImageShiftScale , I found a small problem . the example is ImageInteractor .and my problem is : at first time , I can draw a rectangle on a  CT picture with mouse , and when I press the mouse left button again ,a rectangle could be drawn again but the CT picture disappear  . and I have make the picture to be visibility when I press the left mouse button : 
    pictureActor->VisibilityOn();
and when I release the left mouse button I set it to be invisibility :
    pictureActor->VisibilityOff();
but unfortunately , I could not see the CT picture after I draw a rectangle . So what is wrong with my program ? and how should I do to work out it ? thank you ! 
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