绘制图片直方图

import numpy as np 
from PIL import Image
from matplotlib import pyplot as plt 

img=np.array(Image.open(./img/lena.png).convert(L))

plt.figure("lena")
arr=img.flatten()
n, bins, patches = plt.hist(arr, bins=256, density=1, facecolor='blue', alpha=0.75)  
plt.show()

效果如下