# -*- coding: utf-8 -*-
#face recognition

#import the libraries
import cv2

#loading the cascades
face_cascade = cv2.CascadeClassifier("Haarcascades/haarcascade_frontalface_default.xml")
eye_cascade = cv2.CascadeClassifie("Haarcascades/haarcascade_eye.xml")

#defining a function that will do the detections
def detect(gray, frame):
    faces = face_cascade.detectMultiScale(gray, 1.3, 5)
    for(x,y,w,h)in faces:
        cv2.rectangle(frame, (x,y), (x+w, y+h), (255,0,0), 2)
        rol_gray = gray[y:y+h, x:x+w]
        rol_color = frame[y:y+h, x:x+w]
        eyes = eye_cascade.detectMultiScale(rol_gray, 1.1, 3)
        for(ex, ey, ew, eh) in eyes:
            cv2.rectangle(rol_color, (ex, ey), (ex+ew, ey+eh), (0, 255, 0), 2)
    return frame
    
#doing some face Recognition with the webcam
video_capture = cv2.VideoCapture(0)
while True:
    _, frame = video_capture.read()
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    canvas = detect(gray, frame)
    cv2.imshow('Video', canvas)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
video_capture.release()
cv2.destroyAllWindows()

我在imshow行中得到错误，并给我错误：

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