[Insight-users] how can I make modification to a filter alrea dy exists in ITK?

[Miller, James V (Research)]

There are a couple of ways to this.

If the changes are very local, you might consider adding a mode to the
filter and function to control whether
your modifications are used or not. The code ends up looking like

	if (m_ControlDeformationSmoothing)
	  { 
	  do my new code;
              }
	else
              { 
              do the old code;
              }

This allows the same filter/function to be used and the selection of the
method (original, modified) controlled
by the user.

Another option is create a whole new function/filter combination.  This is
the approach that used when implementing the
SymmmetricForcesDemonsRegistrationFilter/Function and the
LevelSetMotionRegistratonFilter/Function. The amount of code changed for
these "modifications" to the demons algorithm were substantial enough to
warrent new classes. The drawback to this approach is that if there is a
modification that all three filters can benefit from, then you may need to
make the change in multiple places.  

>From what you have written, it sounds like you want to make changes to
PDEDeformableRegistrationFilter::SmoothDeformationField().  You can override
this implementation in a new subclass or patch the original version to
perform in either mode.

There are many variants of the demons algorithm, so I would hesitate to call
your class ModifiedDemonsRegistrationFilter.

Finally, to test your new algorithm, you can either change your local copy
of DeformableRegistration2.cxx to use your new method/filters or you can
create a new example based on the code in DeformableRegistraton2.cxx. 

cp DeformableRegistration2.cxx DeformableRegistration2a.cxx

and then edit DeformableRegistration2a.cxx.  Then, edit the CMakeLists.txt
file in that direction and add an ADD_EXECUTABLE() line similar to the one
for DeformableRegistration2.cxx.  Finally, re-run CMake and build your new
program.

Will you be wanting to submit your modifications to the ITK source tree so
that other researchers can use
them?


-----Original Message-----
From: Guorong Wu [mailto:grwu at sjtu.edu.cn]
Sent: Thursday, July 01, 2004 4:24 AM
To: ITK Mailling List
Subject: [Insight-users] how can I make modification to a filter already
exists in ITK?


hello everyone:
      I am planing to make some improvent to demons algorithms[Thirion
98](Registration/DeformableRegistration2.cxx). Demons algorithm may cause
non-uniform deformation field which will oversmooth at the rigion of lower
contrast. My modification includes: 1. control the force field smoothing
according to gradients by add a weight at each iteration; 2. prevent
oversmoothing the deformation field at lower contrast region with
statistical model at each iteration.
      So I want write a new filter named ModifiedDemonsRegistrationFilter. I
refer to charpter 13 in ITKSoftwareGuide but not quite clear about how to
do. Since I only want to make some modification of force field and
deformation field which could be computered with original
DemonsRegistrationFilter at each iteration, Should I override
PDEDeformableRegistrationFilter and DemonsRegistrationFunction and make
modification there? And another question, Assuming I have writen the filter,
for example, ModifiedDemonsRegistrationFilter.cxx, Should I rebuild ITK to
make it work or simply put it at my personal directory? Thanks. Hoping for
your reply. 
        		

????????Guorong Wu
????????grwu at sjtu.edu.cn
??????????2004-07-01

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Guorong Wu	
The Department of Computer Science and Technology
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