我正在嘗試在python中進行基本的顏色轉換，但是我似乎無法擺脫以下錯誤。

import cv2

img = cv2.imread("people1.jpg")

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
gray = cv2.medianBlur(gray, 3)
edges = cv2.adaptiveThreshold(gray, 255, cv2.ADAPIVE_THRESH_MEAN_C, cv2.THRESH_BINARY, 7, 7)

cv2.imwrite("./uotput_image.jpg", edges)

它出現下面錯誤。

error    Traceback (most recent call last)
<ipython-input-2-d3dd0507c5b7> in <module>()
      8 
      9 img = cv2.imread("people1.jpg")
---> 10 gray = cv2.cvtColor(img, cv2.COLORBGR2GRAY)
     11 gray = cv2.medianBlur(gray, 3)
     12 edges = cv2.adaptiveThreshold(gray, 255, cv2.ADAPIVETHRESHMEANC, cv2.THRESHBINARY, 7, 7)

error: OpenCV(4.1.2) /io/opencv/modules/imgproc/src/color.cpp:182: error: (-215:Assertion failed) !src.empty() in function 'cvtColor'

請問我該怎麼辦?