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from __future__ import print_function
import sys
import cv2 as cv
import matplotlib.pyplot as plt
import numpy as np
def print_help():
print('''
This program demonstrated the use of the discrete Fourier transform (DFT).
The dft of an image is taken and it's power spectrum is displayed.
Usage:
discrete_fourier_transform.py [image_name -- default lena.jpg]''')
def main(argv):
print_help()
filename = argv[0] if len(argv) > 0 else 'lena.jpg'
I = cv.imread(cv.samples.findFile(filename), cv.IMREAD_GRAYSCALE)
if I is None:
print('Error opening image')
return -1
I = cv.resize(I, (0,0), None, fx=1, fy=1)
rows, cols = I.shape
m = cv.getOptimalDFTSize( rows )
n = cv.getOptimalDFTSize( cols )
padded = cv.copyMakeBorder(I, 0, m - rows, 0, n - cols, cv.BORDER_CONSTANT, value=[0, 0, 0])
planes = [np.float32(padded), np.zeros(padded.shape, np.float32)]
complexI = cv.merge(planes) # Add to the expanded another plane with zeros
cv.dft(complexI, complexI) # this way the result may fit in the source matrix
cv.split(complexI, planes) # planes[0] = Re(DFT(I), planes[1] = Im(DFT(I))
cv.magnitude(planes[0], planes[1], planes[0])# planes[0] = magnitude
magI = planes[0]
matOfOnes = np.ones(magI.shape, dtype=magI.dtype)
cv.add(matOfOnes, magI, magI) # switch to logarithmic scale
cv.log(magI, magI)
magI_rows, magI_cols = magI.shape
# crop the spectrum, if it has an odd number of rows or columns
magI = magI[0:(magI_rows & -2), 0:(magI_cols & -2)]
cx = int(magI_rows/2)
cy = int(magI_cols/2)
q0 = magI[0:cx, 0:cy] # Top-Left - Create a ROI per quadrant
q1 = magI[cx:cx+cx, 0:cy] # Top-Right
q2 = magI[0:cx, cy:cy+cy] # Bottom-Left
q3 = magI[cx:cx+cx, cy:cy+cy] # Bottom-Right
tmp = np.copy(q0) # swap quadrants (Top-Left with Bottom-Right)
magI[0:cx, 0:cy] = q3
magI[cx:cx + cx, cy:cy + cy] = tmp
tmp = np.copy(q1) # swap quadrant (Top-Right with Bottom-Left)
magI[cx:cx + cx, 0:cy] = q2
magI[0:cx, cy:cy + cy] = tmp
cv.normalize(magI, magI, 0, 1, cv.NORM_MINMAX) # Transform the matrix with float values into a
cv.imshow("Input Image" , I ) # Show the result
cv.imshow("spectrum magnitude", magI)
cv.imwrite("src\\experiments\\algorithms\\image\\fft.jpg", magI)
cv.waitKey()
x = cv.calcHist([I], [0], None, [256], [0, 256])
plt.plot(x)
plt.show()
if __name__ == "__main__":
main(sys.argv[1:])