There are more than just 3 Gaussians, as images are generally not skull
stripped first. A number of Gaussians are used to model the intensity
distribution of non-brain voxels.
Variances are allowed to vary.
For more details about how it works, you could consult Chapter 5 of
http://www.fil.ion.ucl.ac.uk/spm/doc/books/hbf2/
Best regards,
-John
My understanding of segmentation in SPM2 is that it is based upon a
three component normal mixture model with voxel intensities used as the
feature variables. I would like to know whether the variances of the
mixture components are allowed to vary.
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