Leonard writes:

The picture of the SD9 contains a useful illustration of why blur
filters should be used even when sampling with full colour at each
location.

An antialiasing filter shouldn't be called a "blur filter" because it
doesn't simply blur the image. The ones made from birefringent material
create a controlled multiple image that eliminates information at the
Nyquist frequency while maintaining good contrast up to about 70% of
that limit. A filter that simply blurred a point into a round disc
or a Gaussian shape would lose much more image information below the
Nyquist limit if it was sized to produce reasonable attenuation at the
Nyquist frequency. In filtering terms, the anti-aliasing filter
provides a sharper cutoff than any simply blurring filter.

Foveon's technical reports call an antialiasing filter a "blur filter"
because they don't want to understand the difference, and don't
acknowledge that avoiding aliasing is a good thing. "George" calls it
that too, probably for the same reason. And you *can* use blur to
provide anti-aliasing, it just isn't what cameras with AA filters do.

Dave