How to plot the frequency response of a Discrete Fourier transform on a specific region?

Hi. I need to analyze and implement a simple low pass filter given by the 9x9 point spread function h(m,n), where h(m,n) = 1/81 for m<=4 and n<=4 and h(m,n) = 0 otherwise. I need to plot the magnitude of the frequency response of the discrete fourier transform, H(e^ju, e^jv) over the region [-pi,pi] x [-pi, pi]. How can I plot the DFT over that region? Looking forward for your reply.