Re: [vmtk-users] Level Set segmentation questions

[Carlos A. B. <car...@gm...>]

Hello Luca,
thanks for the answers, i would like to do more questions related to the
subject.

i would like to summarize (in the form of pseudo-code) how i understand the
level set segmentation works, and then ask you some questions

// pseudo-code
begin-------------------------------------------------------------------------------------------------------------
image iI(x) // the -ifile

image lvlSet_t0(x) <--- initialization procedure over the iI(x) image (no
pre-processing is used on iI(x))

image I(x)  // the featured image
if -featureimagefile fI(x) NOT NULL {
  I = fI
}else {
  I = smooth(iI, -smoothingiterations, -smoothingtimestep, -
smoothingconductance)
}
// calculates the G and P
// Where grad operator is defined by -featureimagetype parameter.
image g(x) = G( grad(I) )   // using equation 2.20 from the thesis
image p(x) = P( grad(I) )   // using equation 2.21 from the thesis

// Where -levelsetstype defines the type levelsetFunction to be used
image levelset = levelsetFunction (lvlSet_t0, g, p, -iterations, -propagation,
-curvature, -advection)

// pseudo-code
end--------------------------------------------------------------------------------------------------------------

Questions:
* Which smoothing function is used? (i.e. gradient anisotropic diffusion,
curvature anisotropic diffusion, etc)
* Are G and P functions the ones defined on the thesis? (on
http://www.itk.org/Doxygen/html/classitk_1_1GeodesicActiveContourLevelSetFunction.html
P
is P(G), and in the thesis there is another definition P(I), besides on the
link there are suggestions on the most commonly definition of G, but i'm
not sure on which is really used)


Thanks in advance!
Best of regards
Carlos


2012/12/3 Luca Antiga <luc...@gm...>

> Hello Carlos,
>  welcome to vmtk and sorry for the wait. I hope the timing won't stop you
> from sending more questions in the future.
>
> The level set code I used during my PhD was written by me, then ITK came
> along and I was very happy to fully embrace it :-)
> So right now level set implementation in vmtk is the one provided by ITK:
>
> http://www.itk.org/Doxygen/html/classitk_1_1GeodesicActiveContourLevelSetFunction.html
> which is a specialization of this general formulation
> http://www.itk.org/Doxygen/html/classitk_1_1LevelSetFunction.html
>
> As you see, the latter link includes a spatial modifier for the mean
> curvature term (Z), which in the actually code is
> returned by the CurvatureSpeed method. In the
> GeodesicActiveContourLevelSetFunction such term is set equal to
> G (the edge potential image).
>
> So, long story short, yes, the current implementation follows equation
> 2.22.
>
> Correct me if i'm wrong:  G and P depend on the so called featured Image
> ( | grad I(x) | on Luca's thesis), if executing the
> vmtklevelsetsegmentation filter as before (without specifying a -
> featureimagefile image)  Is the featured image used by G and P calculated
> automatically (depending on the -featureimagetype parameter with gradient
> as default)?
>
>
> Exactly. Good job!
>
>
> Luca
>
>
> On Nov 27, 2012, at 10:19 PM, Carlos Alberto Bulant wrote:
>
> Hi VMTK users,
> this is my first post in this mailing list (probably there will be more),
> i'm a new user just starting to use the toolkit.
> Now to my questions:
>
> When using the level set segmentation filter in the form of :
>
> vmtklevelsetsegmentation -ifile image_volume_voi.vti -ofile level_sets.vti
>
> assuming none-zero PropagationScaling (w1), CurvatureScaling (w2) and
> AdvectionScaling (w3)  parameters, which of the Level Set formulation
> (proposed on Luca Antiga's PhD thesis) does the implementation use?
>
> (2.19)     -w1 G(x) | grad F | + 2 w2 H(x) | grad F | + w3 <[grad P(x)] ,
> grad F >
> (2.22)     -w1 G(x) | grad F | + 2 w2 G(x) H(x) | grad F | + w3 <[grad
> P(x)] , grad F >
>
>
> In the current implementation, are G(x) and P(x) the one proposed on
> Luca's thesis?
>
>
> Correct me if i'm wrong:  G and P depend on the so called featured Image
> ( | grad I(x) | on Luca's thesis), if executing the
> vmtklevelsetsegmentation filter as before (without specifying a -
> featureimagefile image)  Is the featured image used by G and P calculated
> automatically (depending on the -featureimagetype parameter with gradient
> as default)?
>
> Sorry for  my English,
> Best of regards
> Carlos
>
> ------------------------------------------------------------------------------
> Keep yourself connected to Go Parallel:
> DESIGN Expert tips on starting your parallel project right.
>
> http://goparallel.sourceforge.net_______________________________________________
> vmtk-users mailing list
> vmt...@li...
> https://lists.sourceforge.net/lists/listinfo/vmtk-users
>
>
>