Dear John
thanks for your answers. now it is clear for me what is in iy_*.img.
so, if i get it correctly, y_*.img gives a mapping from Xi (voxel in the reference space) to the corresponding coordinates in input image xi (voxel in the subject space). generally, this should be based on affine and nonlinear parametrs.
 
Now, may ques. is that:  i normalize one subject (affine and nonlinear) to the reference image, and want to have only nonlinear vectors, so should i remove the pose parametrs? if yes what is weighting image?
 
Regards
kamran

"Ashburner John (PSYCHOLOGY)" <[log in to unmask]> wrote:
The iy*.img maps from voxels in the individual’s image to the corresponding location in the spatially normalized version.  This location is in units of mm, so you need to consider the voxel-to-world mapping (the matrix returned by spm_get_space) in order to do this.
 
As your spatial normalisation is only affine, then you don’t actually need the iy*.img file.  You can do everything by combining the various affine transforms in the appropriate way.
 
You would not remove any pose parameters.  Removal of pose parameters is only really useful for analysing the shapes of images.
 
Best regards,
-John
 
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On Behalf Of kamran kazemi
Sent: Thursday, December 07, 2006 4:33 PM
To: [log in to unmask]
Subject: [SPM] ques. about deformations and using sn.mat
 
Dear SPMers
 
sorry if my ques. is simple but i confused in using _sn.mat.
 
i want to extract deformation vertos that map voxel xi in the target image to the corresponding voxel (yi) in the affine normalized image.
to extract them:
1- should i use y_*.img or iy_*.img?
2- is it necessery  to remove pose parametrs at first? if yes, which image should used as weighting image, the input image or target image?
 
regards
kamran
 
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