Generate inverse warp images

Algorithms
1

I use rigid registration to get a transformation estimation represented by six numbers (three for rotation, three for translation). And I use the following code to generate the corresponding warp image. I wonder if there is any way to generate an inverse warp image? i.e. transformation from the fixed image to the moving image (Thanks!)

 /** Create an setup displacement field generator. */
  DisplacementFieldGeneratorType::Pointer dispfieldGenerator =
                                                 DisplacementFieldGeneratorType::New();
  dispfieldGenerator->UseReferenceImageOn();
  dispfieldGenerator->SetReferenceImage( fixedImage );
  dispfieldGenerator->SetTransform( outputTransform );
  try
    {
    dispfieldGenerator->Update();
    }
  catch ( itk::ExceptionObject & err )
    {
    std::cerr << "Exception detected while generating deformation field";
    std::cerr << " : "  << err << std::endl;
    return EXIT_FAILURE;
    }

  typedef itk::ImageFileWriter< DisplacementFieldImageType >  FieldWriterType;
  FieldWriterType::Pointer fieldWriter = FieldWriterType::New();

  fieldWriter->SetInput( dispfieldGenerator->GetOutput() );
  fieldWriter->SetFileName( warpFieldName );
  try
    {
    fieldWriter->Update();
    }
  catch( itk::ExceptionObject & excp )
    {
    std::cerr << "Exception thrown " << std::endl;
    std::cerr << excp << std::endl;
    return EXIT_FAILURE;
    }
2

You should try invT = outputTransform.GetInverseTransform(); and then dispfieldGenerator->SetTransform( invT );