PIL - TypeError: src is not a numpy array, neither a scalar

from PIL import Image
import pytesseract
import argparse
import cv2
import os

image  = Image.open("C:/Users/NB/Desktop/Scan/Arti818.jpg")

#image = "C:/Users/NB/Desktop/Scan/Arti818.jpg"
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

# check to see if we should apply thresholding to preprocess the
# image

gray = cv2.threshold(gray, 0, 255,  cv2.THRESH_BINARY | cv2.THRESH_OTSU)[1]

# make a check to see if median blurring should be done to remove
# noise

# write the grayscale image to disk as a temporary file so we can
# apply OCR to it
filename = "{}.png".format(os.getpid())
cv2.imwrite(filename, gray)
# load the image as a PIL/Pillow image, apply OCR, and then delete
# the temporary file
text = pytesseract.image_to_string(Image.open(filename))
os.remove(filename)
print(text)

# show the output images
cv2.imshow("Image", image)
cv2.imshow("Output", gray)
cv2.waitKey(0)

This is my code and I am getting following error:

gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
TypeError: src is not a numpy array, neither a scalar