Don't know how to change images into grayscale under linux

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6

Yes it works if image exist on disk

you should write (tutorials here ):

import cv2 as cv
import sys
img = cv.imread("starry_night.jpg")
if img is None:
    sys.exit("Could not read the image.")
cv.imshow("Display window", img)
k = cv.waitKey(0)
if k == ord("s"):
    cv.imwrite("starry_night.png", img)
k = cv.waitKey(0)

give full path to image