cv2图片转像素这是咋回事

这是咋回事

Traceback (most recent call last):
  File "C:/Users/Administrator/Desktop/python/像素图片转换.py", line 3, in 
    grey = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
cv2.error: OpenCV(4.6.0) D:\a\opencv-python\opencv-python\opencv\modules\imgproc\src\color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'

我也遇过这种情况，好像