numpy array和灰度图的互相转换

import numpy as np
from PIL import Image

#np.array2image_gray
size = 512
# a = np.random.rand(size*size).reshape((size,size))*255
a=np.linspace(0,1,size*size).reshape((size,size))*255#值范围[0,255]
a = a.astype('uint8')
a_image_gray = Image.fromarray(a,'L')
a_image_gray.show()
a_image_gray.save(r'a_image_gray.jpg')

#image_gray2np.array
image_f = Image.open("a_image_gray.jpg")
image_array = np.array(image_f)

a和image_array好像不太一样，不知道为什么，有空再说