On Fri 2008/05/30 12:48:46 +1000, Mark Calabretta wrote
in a message to: Jonathan McDowell ,
Eric Greisen
and copied to:

consequently a centre. As I explained previously, in terms of Fourier
sampling theory what we call an "image" is actually a shah function.

See
http://en.wikipedia.org/wiki/Dirac_comb
http://mathworld.wolfram.com/ShahFunction.html