使用PIL python计算灰度的errorType

我试图在python上计算图片的灰度 公式数学为:

ndg = red*0.299+green*0.587+blue*0.114

但是类型错误

TypeError: 'JpegImageFile' object is not subscriptable

代码开始于

from PIL import Image

img = Image.open("C://Users/shous/Desktop/houssem.jpg")
pix = img.load()
cols,rows = img.size

def ndg(img,rows,cols):
   mat = [[0 for x in range(cols)] for y in range(rows)]
    for x in range(cols):
       for y in range(rows):
           mat[x][y] = 0
    for x in range(cols):
        for y in range(rows):
            val = img[x, y]  # <<== error type

            mat[x][y] = val[2]*0.299+val[1]*0.587+val[0]*0.114
            print(mat[x][y])
    return mat

print('mat ',ndg(img,rows,cols))

错误消息为:

File "C:/Users/shous/PycharmProjects/Compar/Compare.py", line 145, in <module>
    val = img[x, y]
TypeError: 'JpegImageFile' object is not subscriptable