frequency spectrum fft2

About frequency analysis of luminance image (csv). I am dealing with images (luminance image 3840 x 3841) and I want to analyze the frequency (cycle/degree). What you want to know is how many frequencies are included (in frequency spectrum etc.). I don't understand the procedure after doing the two-dimensional Fourier transform (fft2). The sampling frequency is 128.2 cycle/degree. Please tell me the commands to display the spectrum.