Convolution
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