In order to simplify our analysis we will consider 1-D signals for the moment.
It will be straightforward to extend the result to 2-D.
Some operations that are diffcult to compute in the spatial domain are simplified when
the function is tranformed to its dual representation in the frequency domain. One such
function is convolution.
Convolution describes how a system with impulse response, h(x), reacts to a signal, f(x).
This integral evaluation is equivalent to multiplication in the frequency domain
The converse is also true