问```cv2_imshow()`中出现'NoneType‘对象没有属性'clip’错误

EN

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-47-e0549b59dd89> in <module>()
     47         print("\n\n")
     48 
---> 49     cv2_imshow(frame)
     50     if cv2.waitKey(1) & 0xFF == ord('q'):
     51         break

/usr/local/lib/python3.6/dist-packages/google/colab/patches/__init__.py in cv2_imshow(a)
     20       image.
     21   """
---> 22   a = a.clip(0, 255).astype('uint8')
     23   # cv2 stores colors as BGR; convert to RGB
     24   if a.ndim == 3:

AttributeError: 'NoneType' object has no attribute 'clip'

from google.colab.patches import cv2_imshow
from keras.models import load_model
from time import sleep
from keras.preprocessing.image import img_to_array
from keras.preprocessing import image
import cv2
import numpy as np

face_classifier = cv2.CascadeClassifier('/content/drive/My Drive/Colab Notebooks/haarcascade_frontalface_default.xml')
classifier = load_model('/content/drive/My Drive/Colab Notebooks/fer_68acc.h5')

class_labels = ['Angry','Happy','Neutral','Sad','Surprise']

cap = cv2.VideoCapture(0)



while True:
    # Grab a single frame of video
    ret, frame = cap.read()
    labels = []
    gray = cv2.imread(frame, cv2.IMREAD_GRAYSCALE)
    faces = face_classifier.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)
        roi_gray = gray[y:y+h,x:x+w]
        roi_gray = cv2.resize(roi_gray,(48,48),interpolation=cv2.INTER_AREA)


        if np.sum([roi_gray])!=0:
            roi = roi_gray.astype('float')/255.0
            roi = img_to_array(roi)
            roi = np.expand_dims(roi,axis=0)

        # make a prediction on the ROI, then lookup the class

            preds = classifier.predict(roi)[0]
            print("\nprediction = ",preds)
            label=class_labels[preds.argmax()]
            print("\nprediction max = ",preds.argmax())
            print("\nlabel = ",label)
            label_position = (x,y)
            cv2.putText(frame,label,label_position,cv2.FONT_HERSHEY_SIMPLEX,2,(0,255,0),3)
        else:
            cv2.putText(frame,'No Face Found',(20,60),cv2.FONT_HERSHEY_SIMPLEX,2,(0,255,0),3)
        print("\n\n")
    
    cv2_imshow(frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()