text: import cv2
  import numpy as np
  from matplotlib import pyplot as plt
  
  img = cv2.imread('messi5.jpg',0)
  f = np.fft.fft2(img)
  fshift = np.fft.fftshift(f)
  magnitude_spectrum = 20*np.log(np.abs(fshift))
  
  plt.subplot(121),plt.imshow(img, cmap = 'gray')
  plt.title('Input Image'), plt.xticks([]), plt.yticks([])
  plt.subplot(122),plt.imshow(magnitude_spectrum, cmap = 'gray')
  plt.title('Magnitude Spectrum'), plt.xticks([]), plt.yticks([])
  plt.show()
  
  
  img = cv2.imread('messi5.jpg',0)
  rows, cols = img.shape
  crow,ccol = rows/2 , cols/2
  fshift[crow-30:crow+30, ccol-30:ccol+30] = 0
  f_ishift = np.fft.ifftshift(fshift)
  img_back = np.fft.ifft2(f_ishift)
  img_back = np.abs(img_back)
  
  plt.subplot(131),plt.imshow(img, cmap = 'gray')
  plt.title('Input Image'), plt.xticks([]), plt.yticks([])
  plt.subplot(132),plt.imshow(img_back, cmap = 'gray')
  plt.title('Image after HPF'), plt.xticks([]), plt.yticks([])
  plt.subplot(133),plt.imshow(img_back)
  plt.title('Result in JET'), plt.xticks([]), plt.yticks([])
  
  plt.show()
  
  
  # Fourier Transform in OpenCV
  import cv2
  from matplotlib import pyplot as plt
  
  img = cv2.imread('messi5.jpg',0)
  
  dft = cv2.dft(np.float32(img),flags = cv2.DFT_COMPLEX_OUTPUT)
  dft_shift = np.fft.fftshift(dft)
  
  magnitude_spectrum = 20*np.log(cv2.magnitude(dft_shift[:,:,0],dft_shift[:,:,1]))
  
  plt.subplot(121),plt.imshow(img, cmap = 'gray')
  plt.title('Input Image'), plt.xticks([]), plt.yticks([])
  plt.subplot(122),plt.imshow(magnitude_spectrum, cmap = 'gray')
  plt.title('Magnitude Spectrum'), plt.xticks([]), plt.yticks([])
  plt.show()
  
  rows, cols = img.shape
  crow,ccol = rows/2 , cols/2
  
  # create a mask first, center square is 1, remaining all zeros
  mask = np.zeros((rows,cols,2),np.uint8)
  mask[crow-30:crow+30, ccol-30:ccol+30] = 1
  
  # apply mask and inverse DFT
  fshift = dft_shift*mask
  f_ishift = np.fft.ifftshift(fshift)
  img_back = cv2.idft(f_ishift)
  img_back = cv2.magnitude(img_back[:,:,0],img_back[:,:,1])
  
  plt.subplot(121),plt.imshow(img, cmap = 'gray')
  plt.title('Input Image'), plt.xticks([]), plt.yticks([])
  plt.subplot(122),plt.imshow(img_back, cmap = 'gray')
  plt.title('Magnitude Spectrum'), plt.xticks([]), plt.yticks([])
  plt.show()