jpg_spatial_frequency.py

import cv2
import numpy as np
from matplotlib import pyplot as plt

raw_img = cv2.imread('unsw_bw.jpg',0)

raw_img = (raw_img /255.0) *2.0 - 1.0 # convert to -1:+1 range
rms = 0.2

raw_img = raw_img - np.mean(raw_img)  # make mean to be zero
raw_img = raw_img / np.std(raw_img)   # make standard deviation to be 1
raw_img = raw_img * rms

img_freq = np.fft.fft2(raw_img) # convert to frequency domain
img_amp  = np.fft.fftshift(np.abs(img_freq)) # calculate amplitude spectrum
img_amp_disp = np.log(img_amp + 0.0001) # take logarithm for display
img_amp_disp = ((( img_amp_disp - np.min(img_amp_disp)) * 2)/ np.ptp(img_amp_disp)) -1

plt.imshow(img_amp_disp, cmap='gray')
plt.axis('off')
plt.show()