[Insight-users] deformation field accumulation

[Luis Ibanez]

Hi Minjie,

The

        itkDemonsRegistrationImageFilter

derives from the class:

        itkPDEDeformableRegistrationFilter

which in turs derives from:

        itkDenseFiniteDifferenceImageFilter


The method "ComputUpdate()" is invoked through a virtual
function in DenseFiniteDifferenceImageFilter.


The DemonsRegistartionFunction computes the update of the
deformation field at every pixel.

A multi-threaded method in the DenseFiniteDifferenceImageFilter
cumulates the updates into the final deformation field.

This method is called ThreadedApplyUpdate, in lines 195-212
of the file


Insight/Code/Common/itkDenseFiniteDifferenceImageFilter.txx



void
DenseFiniteDifferenceImageFilter<TInputImage, TOutputImage>
::ThreadedApplyUpdate(TimeStepType dt, const ThreadRegionType 
&regionToProcess,
                       int)
{
   ImageRegionIterator<UpdateBufferType> u(m_UpdateBuffer, 
regionToProcess);
   ImageRegionIterator<OutputImageType>  o(this->GetOutput(), 
regionToProcess);

   u = u.Begin();
   o = o.Begin();

   while ( !u.IsAtEnd() )
     {
     o.Value() += static_cast<PixelType>(u.Value() * dt);  // no adaptor 
support here
     ++o;
     ++u;
     }
}






The code that you are looking for is in line 208 above.


    Regards,


       Luis




-----------------
Minjie Wu wrote:
> Dear All, 
> 
> I am trying to look into the ITK demons registration code and have some 
> difficulties in understanding the accumulation of the deformation field 
> between iterations. 
> 
> As in demons registration algorithm, the updating deformation field was 
> u =  (g-f) *grad(f)/((g-f)^2+grad_mag^2).
> 
> My question is: 
> How u is used to update the deformation from the previous iteration f_pre 
> (previous deformation)? was it simple addition? the new deformation 
> field f_new  =  f_pre + u? 
> 
> I wasn't be able to find the function in the ITK registration codes for this
> field updating, and I appreciate if anyone can help me with any 
> information. 
> 
> Thanks,
> -Minjie Wu 
> 
> 
> ------------------------------------------------------------------------
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