Opencv2 cvtColor（） 在树莓派上不起作用？

问：

我正在根据youtube教程编写python opencv2 python代码，这里我直接复制了代码，

import cv2
import utlis

###################################
webcam = True
path = '/home/ftsp23/vert/phone'
cap = cv2.VideoCapture(0)
cap.set(10,160)
cap.set(3,1920)
cap.set(4,1080)
scale = 3
wP = 210 *scale
hP= 297 *scale
###################################

while True:
    if webcam:success,img = cap.read()
    else: img = cv2.imread(path)

    imgContours , conts = utlis.getContours(img,minArea=50000,filter=4)
    if len(conts) != 0:
        biggest = conts[0][2]
        #print(biggest)
        imgWarp = utlis.warpImg(img, biggest, wP,hP)
        imgContours2, conts2 = utlis.getContours(imgWarp,
                                                 minArea=2000, filter=4,
                                                 cThr=[50,50],draw = False)
        if len(conts) != 0:
            for obj in conts2:
                cv2.polylines(imgContours2,[obj[2]],True,(0,255,0),2)
                nPoints = utlis.reorder(obj[2])
                nW = round((utlis.findDis(nPoints[0][0]//scale,nPoints[1][0]//scale)/10),1)
                nH = round((utlis.findDis(nPoints[0][0]//scale,nPoints[2][0]//scale)/10),1)
                cv2.arrowedLine(imgContours2, (nPoints[0][0][0], nPoints[0][0][1]), (nPoints[1][0][0], nPoints[1][0][1]),
                                (255, 0, 255), 3, 8, 0, 0.05)
                cv2.arrowedLine(imgContours2, (nPoints[0][0][0], nPoints[0][0][1]), (nPoints[2][0][0], nPoints[2][0][1]),
                                (255, 0, 255), 3, 8, 0, 0.05)
                x, y, w, h = obj[3]
                cv2.putText(imgContours2, '{}cm'.format(nW), (x + 30, y - 10), cv2.FONT_HERSHEY_COMPLEX_SMALL, 1.5,
                            (255, 0, 255), 2)
                cv2.putText(imgContours2, '{}cm'.format(nH), (x - 70, y + h // 2), cv2.FONT_HERSHEY_COMPLEX_SMALL, 1.5,
                            (255, 0, 255), 2)
        cv2.imshow('A4', imgContours2)

    img = cv2.resize(img,(0,0),None,0.5,0.5)
    cv2.imshow('Original',img)
    cv2.waitKey(1)

但它返回的错误

Traceback (most recent call last):
  File "/home/ftsp23/vert/aaa.py", line 24, in <module>
    imgContours , conts = utlis.getContours(img,minArea=50000,filter=4)
  File "/home/ftsp23/vert/utlis.py", line 6, in getContours
    imgGray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
cv2.error: OpenCV(4.6.0) /tmp/pip-wheel-u79916uk/opencv-python_ea2489746b3a43bfb3f2b5331b7ab47a/opencv/modules/imgproc/src/color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cvtColor'

我正在树莓派上运行代码，python 版本 3.9.2，使用版本 4.6.0.66（我们必须使用此版本，因为上面的任何版本都不起作用），我已经尝试了多次尝试来修复错误无济于事，如果有人有任何见解或建议，我可以尝试，将不胜感激。谢谢。