I have applied the Fourier transformation on an image like so:
I = imread('img.jpg');
img = fftshift(I);
F = fft2(img);
magnitude = mat2gray(100*log(1+abs(fftshift(F)))); % Magnitude spectrum
phase = mat2gray( (angle(F)) ); % Phase spectrum
Using the energy compaction property of the Discrete Fourier Transform how can I extract a 21x21 matrix of the low-frequency value coefficients of the Fourier transformation?
Thanks in advance!