> Well, in fact image.smooth() this code are slightly different. image.smooth()
> processes each image independently, whereas this code concatenates all 3D
> images. Using image.smooth() would require adding a concat_niimgs() somewhere,
> which would be kind of awkward (lots of conversion between different formats).
> I think I'll let things like this for the moment, time to think of a cleaner
> solution.

What does image.smooth return when given a 4D niimg? I would believe that
it should return a concatenated img.