import numpy as np

import matplotlib.pyplot as plt

x = np.linspace(-10, 10, 1000)

a = np.cos(x)

b = a + np.cos(3 * x)

# d = np.log(x)

c = b + np.cos(7 * x)

d = c - np.cos(10 * x)

plt.subplot(2, 2, 1)

plt.plot(x, a, label=‘$cos(x)$‘, color=‘green‘, linewidth=1)

plt.title("cosx")

plt.xlim(-2, 2)

plt.ylim(-3, 3)

plt.subplot(2, 2, 2)

plt.plot(x, b, label=‘$cos(x)+cos(3x)$‘, color=‘red‘, linewidth=1)

plt.title("cosx+cos(3x)")

plt.xlim(-2, 2)

plt.ylim(-3, 3)

plt.subplot(2, 2, 4)

plt.plot(x, d, label=‘$cos(x)+cos(3x)+cos(7x)$‘, color=‘blue‘, linewidth=1)

plt.title("cosx+cos(3x)+cos(7x)-cos(10x)")

plt.xlim(-2, 2)

plt.ylim(-3, 3)

plt.subplot(2, 2, 3)

plt.plot(x, c, label=‘$cos(x)+cos(3x)+cos(7x)$‘, color=‘black‘, linewidth=1)

plt.title("cosx+cos(3x)+cos(7x)")

plt.xlim(-2, 2)

plt.ylim(-3, 3)

plt.show()

import cv2 as cv

import numpy as np

import matplotlib.pyplot as plt

img = cv.imread(‘learn.jpg‘, 0) #直接读为灰度图像

f = np.fft.fft2(img) #做频率变换

fshift = np.fft.fftshift(f) #转移像素做幅度普

s1 = np.log(np.abs(fshift))#取绝对值：将复数变化成实数取对数的目的为了将数据变化到0-255

plt.subplot(121)

plt.imshow(img, ‘gray‘)

plt.title(‘original‘)

plt.subplot(122)

plt.imshow(s1,‘gray‘)

plt.title(‘center‘)

plt.show()