[Insight-users] confused by muti-scale frame work with physical space processing in ITK

[Baoyun Li]

Dear Luis and All:

I am confused by muti-scale frame work with physical space processing in ITK. Let take Level set for segmenation as example, the original data is 1mm, and I will do the 3 reolution level for level set (4,2,1 mm) 

1 I fully understand what happen in voxle space. we have intial level set, at high resolution, the distance of initial levels set may be too far to the true contour( let say 10mm or 10 voxle), then we go to 4mm, and the distance is only 2.5 voxels. So muti-scale processing help the level set to converge to the truth quickly.

2. But if we process it in the ITK framework or say physical space, even at low resolution, the distance is still 10mm and is not reduced. How this muti -scale scheme helps to speed up the algorithm?

3 I guess, even we say ITK is in physical space, but in real processing, e.g, (at 4mm level), the program will only work on the grid point. But the programm knows clearly that is 4mm voxle distance. The step is 4 time bigger than high resolution case.( I guess).


I understand this question may be too naive, but I am really confused.


Thanks

Baoyun


      
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