The Gray map from
to binary pairs is the bijection
,
,
, and
,
extended coordinatewise to words over
.
It takes a length-
quaternary code to a length-
binary code. Its binary image need
not be a linear code, even when the quaternary code is linear over the ring
.
The modified binary Preparata-like codes of Hammons et al. (1994) are Gray images of linear codes over .