High Pass Filter for image processing in python by using scipy/numpy

Question

I am currently studying image processing. In Scipy, I know there is one median filter in Scipy.signal. Can anyone tell me if there is one filter similar to high pass filter?

Answer 1

Here is how we can design a HPF with scipy fftpack

from skimage.io import imread
import matplotlib.pyplot as plt
import scipy.fftpack as fp

im = np.mean(imread('../images/lena.jpg'), axis=2) # assuming an RGB image
plt.figure(figsize=(10,10))
plt.imshow(im, cmap=plt.cm.gray)
plt.axis('off')
plt.show()

Original Image

F1 = fftpack.fft2((im).astype(float))
F2 = fftpack.fftshift(F1)
plt.figure(figsize=(10,10))
plt.imshow( (20*np.log10( 0.1 + F2)).astype(int), cmap=plt.cm.gray)
plt.show()

Frequency Spectrum with FFT

(w, h) = im.shape
half_w, half_h = int(w/2), int(h/2)

# high pass filter
n = 25
F2[half_w-n:half_w+n+1,half_h-n:half_h+n+1] = 0 # select all but the first 50x50 (low) frequencies
plt.figure(figsize=(10,10))
plt.imshow( (20*np.log10( 0.1 + F2)).astype(int))
plt.show()

Block low Frequencies in the Spectrum

im1 = fp.ifft2(fftpack.ifftshift(F2)).real
plt.figure(figsize=(10,10))
plt.imshow(im1, cmap='gray')
plt.axis('off')
plt.show()

Output Image after applying the HPF