> > It is the "Remove pose from deformations" option that asks for a
> > weighting image. This option removes rotations, translations and
> > possibly an isotropic zoom from a deformation field such that it
> > can be thought of as encoding only shape.
>
> This will remove the effect of differing head positions by removing
> rotations and translations; my question is, does the removal of an
> isotropic zoom ("yes" to the "remove size"-question) mean that the
> effect of the linear scaling is fully removed from the field ? In my
> understanding, this would effectively leave you with an image that only
> encodes the non-linear component of the normalization.
The affine component of SPM's spatial normalisation is paramaterised by 12
parameters, 3 translations, three rotations, three orthogonal zooms and three
shears. "Removing size" will result in a warp that has 7 parameters removed
from it - the 3 rotations, 3 translations and a single isotropic zoom. i.e., it removes
the effect of size and pose from the warps, leaving only shape information.
Therefore, some of the affine part of the spatial normalisation will remain in the
adjusted (Procrustes corrected) warps.
Best regards,
-John
--
Dr John Ashburner.
Functional Imaging Lab., 12 Queen Square, London WC1N 3BG, UK.
tel: +44 (0)20 78337491 or +44 (0)20 78373611 x4381
fax: +44 (0)20 78131420 http://www.fil.ion.ucl.ac.uk/~john
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