[vtkusers] vtkImageTracerWidget & vtkBMPWriter

[JohnMark]

Hello , vtkusers ,
    I want to extract any regions from a 2D CT slice , so I use the vtkImageTracerWidget . surely , it is perfect , I can clip any regions . but there is the problem coming : I want to save the result with vtkBMPWriter :
 
vtkImageCast * readerImageCast = vtkImageCast::New();
// its data from the output of vtkImageStencil
readerImageCast->SetInput((vtkDataObject *)stencil->GetOutput()); 
readerImageCast->SetOutputScalarTypeToUnsignedChar();vtkBMPWriter * bmp = vtkBMPWriter::New();
bmp->SetInput(readerImageCast1->GetOutput());
bmp->SetFileName("C:/test.bmp");    
bmp->Write(); // problem !!!! it does not work any more !    
bmp->Update();
 
    however , it does not work , what I got is just a black line ( nothing ) . and then I change my method , I add a KeyReleaseEvent and a AddObserver of vtkRenderWindowInteractor , the render window would capture the message when the key was released and I get the region , then I will save the result , but I still get nothing .
    
    so what is wrong with my thinking ? and I know the vtkImageTracerWidget class wrap the vtkImageViewer , vtkActor and so on , I can save the result rendering in the vtkImageViewer , but I can do nothing with the result of vtkImageTracerWidget . we can not save the result but just to see it , isn't it ? if it is not , is there any method or any class to save it ?  
 
    thank you with great regards ! and waiting for your answer !
    
    Mark
 
    PS . this is a problem I have been thinking for almost a month , I still get nothing now . 
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