[Insight-users] DenseFiniteDifferenceImageFilter and Pipelines

[Tom Vercauteren]

[Text only version... I forgot insight-users mail were better in plain text]

Hi Luis,

Thanks for your reply. Rereading my mail, convinced myself I wasn't
really clear. I'll do my best to make myself clearer this time.

Let's look at the DemonsRegistrationFilter. Suppose I want to change the
DemonsRegistrationFilter::ApplyUpdate(TimeStepType dt) function using
some ITK filters. To make it simple, we can simply change (within this
function) the call to Superclass::ApplyUpdate(dt) by a combination of
a ShiftScaleImageFilter and an AddImageFilter:

In DemonsRegistrationFilter::ApplyUpdate(TimeStepType dt) instead of:
  this->Superclass::ApplyUpdate(dt);

Use the following:
  // Without the call to this->GetUpdateBuffer()->Modified() the shiftscale
  // and add filters are only updated during the first iteration
  // this->GetUpdateBuffer()->Modified();

  //replace the Superclass::ApplyUpdate(dt) by a scale and an add filter
  typedef ShiftScaleImageFilter<
      DeformationFieldType, DeformationFieldType> ScalerType;
  typedef AddImageFilter<
      DeformationFieldType, DeformationFieldType,
DeformationFieldType> AdderType;

  ScalerType::Pointer scaler = ScalerType::New();
  AdderType::Pointer  adder  = AdderType::New();
  scaler->SetScale(dt);
  scaler->SetShift(0.0);
  scaler->SetInput( this->GetUpdateBuffer() );
  adder->SetInput( scaler->GetOutput() );
  adder->GraftOutput( this->GetOutput() );
  adder->Update();
  // Region passing stuff
  this->GraftOutput( m_Adder->GetOutput() );


If we don't explicitely call this->GetUpdateBuffer()->Modified()
before the adder->Update(), then this adder->Update() is only
effective ly computed during the first iteration.

Best regards,
Tom Vercauteren