[Insight-users] Visualization of Deformable Deformation Fields

[Karthik Krishnan]

On Sun, 2006-01-15 at 13:25 -0800, Kevin Ming wrote:
> Hi,
> 
> First off, I have a general question about the deformation field
> generated from a deformable registration process in ITK:   What is
> contained in the output file, and how does a software like ParaView
> use that file to produce a vector-based image using the equation:
> 
> iHat*ImageFile_0 + jHat*ImageFile_1 + kHat*ImageFile_2 
> 
> So I guess, to put it in different words, what do the different
> components of the above equation mean?
> 

Each component image represents the component of the deformation along
that direction (x, y and z)

The field written by the example in ITK is just a multi-component image 
itk::Image< Vector< T, 3 >, ImageDimension >

> In terms of the specific question I have regarding visualization of
> deformation fields in ParaView:  
> 
> 1)  How come the deformation field output produced from ITK's
> deformable registration algorithms came out upside-down for me when
> viewed using ParaView?  That is, the image is flipped
> vertically/mirrored along the x-axis.
> 

Graphics vs math convention:
origin top left - origin bottom left.
That said, if you saved the data in a format that stores origin
information like MetaImage, ... and query the value at location (x,y,z),
they should be same in both cases. Its just that you are looking at the
Y axis from the opposite direction.

> 2)  How come the deformation field resulting from, say, the Demons 1
> registration algorithm came out so scattered and non-uniform for me,
> unlike the deformation field produced by the FEM-based algorithm?
> 
Do you want to regularize the deformation field ? 
See
http://www.itk.org/Insight/Doxygen/html/d2/dda/classitk_1_1DemonsRegistrationFilter-members.html

SetSmoothDeformationField(true);

> Please note that I've made no modifications to any of the ITK
> algorithms described above. 
> 
> 
> Thank you very much,
> Kevin 
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