Python エラ (-215:Assertion failed) !empty() in function 'cv::CascadeClassifier::detectMultiScale'

pythonを使ってwebカメラ上で、瞳の検出を行いたいのですが、グレー変換をする際にエラーが出てきます。昨日までエラー無くできていたので困っています。

発生している問題・エラーメッセージ

python
1error: OpenCV(4.2.0) C:\projects\opencv-python\opencv\modules\imgproc\src\color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'
2

該当のソースコード

python
1    gray = cv2.cvtColor(rgb, cv2.COLOR_RGB2GRAY)
2    faces = face_cascade.detectMultiScale(
3    gray, scaleFactor=1.11, minNeighbors=3, minSize=(100, 100))
4

全体のソースコード

python
1import os,sys
2import cv2
3import dlib
4from imutils import face_utils
5from scipy.spatial import distance
6
7
8
9cap = cv2.VideoCapture(0)
10face_cascade = cv2.CascadeClassifier('Users/User/Documents/eye/opencv-4.2.0/data/haarcascades/haarcascade_frontalface_alt2.xml')
11face_parts_detector = dlib.shape_predictor('shape_predictor_68_face_landmarks.dat')
12
13def calc_ear(eye):
14    A = distance.euclidean(eye[1], eye[5])
15    B = distance.euclidean(eye[2], eye[4])
16    C = distance.euclidean(eye[0], eye[3])
17    eye_ear = (A + B) / (2.0 * C)
18    return round(eye_ear, 3)
19
20def eye_marker(face_mat, position):
21    for i, ((x, y)) in enumerate(position):
22        cv2.circle(face_mat, (x, y), 1, (255, 255, 255), -1)
23        cv2.putText(face_mat, str(i), (x + 2, y - 2), cv2.FONT_HERSHEY_SIMPLEX, 0.3, (255, 255, 255), 1)
24
25while True:
26    tick = cv2.getTickCount()
27
28    ret, rgb = cap.read()
29    gray = cv2.cvtColor(rgb, cv2.COLOR_RGB2GRAY)
30    faces = face_cascade.detectMultiScale(
31    gray, scaleFactor=1.11, minNeighbors=3, minSize=(100, 100))
32
33    if len(faces) == 1:
34        x, y, w, h = faces[0, :]
35        cv2.rectangle(rgb, (x, y), (x + w, y + h), (255, 0, 0), 2)
36
37        face_gray = gray[y :(y + h), x :(x + w)]
38        scale = 480 / h
39        face_gray_resized = cv2.resize(face_gray, dsize=None, fx=scale, fy=scale)
40
41        face = dlib.rectangle(0, 0, face_gray_resized.shape[1], face_gray_resized.shape[0])
42        face_parts = face_parts_detector(face_gray_resized, face)
43        face_parts = face_utils.shape_to_np(face_parts)
44
45        left_eye = face_parts[42:48]
46        eye_marker(face_gray_resized, left_eye)
47
48        left_eye_ear = calc_ear(left_eye)
49        cv2.putText(rgb, "LEFT eye EAR:{} ".format(left_eye_ear), 
50            (10, 100), cv2.FONT_HERSHEY_PLAIN, 1, (0, 0, 255), 1, cv2.LINE_AA)
51
52        right_eye = face_parts[36:42]
53        eye_marker(face_gray_resized, right_eye)
54
55        right_eye_ear = calc_ear(right_eye)
56        cv2.putText(rgb, "RIGHT eye EAR:{} ".format(round(right_eye_ear, 3)), 
57            (10, 120), cv2.FONT_HERSHEY_PLAIN, 1, (0, 0, 255), 1, cv2.LINE_AA)
58
59        if (left_eye_ear + right_eye_ear) < 0.55:
60            cv2.putText(rgb,"close",
61                (10,180), cv2.FONT_HERSHEY_PLAIN, 3, (0,0,255), 3, 1)
62
63        cv2.imshow('frame_resize', face_gray_resized)
64
65    fps = cv2.getTickFrequency() / (cv2.getTickCount() - tick)
66    cv2.putText(rgb, "FPS:{} ".format(int(fps)), 
67        (10, 50), cv2.FONT_HERSHEY_PLAIN, 2, (0, 0, 255), 2, cv2.LINE_AA)
68
69    cv2.imshow('frame', rgb)
70    if cv2.waitKey(1) == 27:
71        break  # esc to quit
72
73cap.release()
74cv2.destroyAllWindows()