_vtkimageviewer2->GetRenderer()->GradientBackgroundOn();
_vtkimageviewer2->GetRenderer()->SetBackground( 0.33 , 0.33 , 0.33 );
_vtkimageviewer2->GetRenderer()->SetBackground2( 0.66 , 0.66 , 0.66 );
_vtkimageviewer2->GetRenderer()->GradientBackgroundOn();
_vtkimageviewer2->GetRenderer()->SetBackground( 0.33 , 0.33 , 0.33 );
_vtkimageviewer2->GetRenderer()->SetBackground2( 0.66 , 0.66 , 0.66 );