Periodogram and Image Processing

Hello all, How can i calculate and extract the periodogram for a Gray-Image(MxN) and then plot it ?

Answer 1

[Wayne King]

xdft=fft2(x);
xdft=xdft.*conj(xdft);
xdft=xdft/(size(x,1)*size(x,2));
xdft=fftshift(xdft);
surf(xdft);