I've been trying to implement an homomorphic filter in frequency domain on both MATLAB and Python using OpenCV2 and NumPy, the MATLAB code gives the expected answer but the Python does not, the resulting image is very weird. I've tested all variables and came to the conclusion the only point there is a difference is the IFFT. On MATLAB, the results can be applied normally to the exp
function and return the filtered original image expected, but the values of Python ifft
are very different. I happened to see other posts with similar problems, but no satisfactory answer (perhaps i'm just bad at searching too...).
The MATLAB code
function [ img_r ] = homomorphic( img, D0, n )
[N, M] = size(img);
img_bk = double(img);
img_bk = log(img_bk+1);
img_freq = fftshift(fft2(img_bk));
magA = uint8(10*log(1+abs(img_freq)));
cu = M/2;
cv = N/2;
Hf = zeros(N,M);
for v = 1:N
dv = v - cv;
for u = 1:M
du = u - cu;
D = sqrt(du*du + dv*dv);
num = 1;
if D > 0
den = 1+((D0/D)^(2*n));
else
den = 0; %to replace +inf
end
if den ~= 0
H = num/den;
else
H = 0;
end
img_freq(v,u) = H*img_freq(v,u);
end
end
magB = uint8(10*log(1+abs(img_freq)));
img_r = (ifft2(ifftshift(img_freq)));
img_r = exp(img_r);
img_r = uint8(img_r);
and the Python code (might have some bugs but overall works)
import numpy as np
import cv2
def homomorphic(img, D0, n=2):
[N,M] = img.shape
img_bk = np.log(1 + np.float64(img))
img_freq = np.fft.fftshift(np.fft.fft2(img_bk))
cu = M/2.0
cv = N/2.0
for v in range(N):
dv = v - cv
for u in range(M):
du = u - cu
D = np.sqrt(du*du + dv*dv)
if D != 0:
a = 1.0 + (D0/D)**(2*n)
H = 1/a
else:
print D
H = 0
img_freq[v][u] = H*img_freq[v][u]
img_r = np.abs(np.fft.ifft2(np.fft.ifftshift(img_freq)))
eimg = np.exp(img_r)
eimg = np.uint8(eimg)
return eimg
I really don't get it, why the results are so different? Does anyone have any idea?