Python OpenCV3在视频上写入文本

我有树莓皮3与树莓杰西安装。OpenCV3和python 3.0也已安装。我得到了一个检测人脸的python示例代码。我需要在屏幕上写一些文字，但不是写在上面。我需要写一次文本，而不是在每个面上重复。下面是代码

import cv2
import sys
from tkinter import *
from tkinter import messagebox

faceCascade =  cv2.CascadeClassifier('haarcascade_frontalface_default.xml')

video_capture = cv2.VideoCapture(0)
video_capture.set(3,500)
video_capture.set(4,300)
video_capture.set(12, 0.1)

frameWidth = int(video_capture.get(cv2.CAP_PROP_FRAME_WIDTH))
frameHeight = int(video_capture.get(cv2.CAP_PROP_FRAME_HEIGHT))

while True:
# Capture frame-by-frame
ret, frame = video_capture.read()

gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

faces = faceCascade.detectMultiScale(
    gray,
    scaleFactor=1.1,
    minNeighbors=5,
    minSize=(30, 30),
    flags=cv2.CASCADE_SCALE_IMAGE
)

# Draw a rectangle around the faces
for (x, y, w, h) in faces:
    cv2.rectangle(frame, (x, y), (x+w, y+h), (0, 255, 0), 2)
    #cv2.putText(frame, 'How are you', (x - 1, y - 1), cv2.FONT_HERSHEY_PLAIN,2,(0, 255, 0)) 
 #if the puttext at here, it will write the text on top of each face detected.  But I just need the text appear once.

# Display the resulting frame
cv2.imshow('Video', frame)


if len(faces) > 0:
    cv2.putText(img = frame, text = 'How are you', org = (int(frameWidth/2 - 20),int(frameHeight/2)), fontFace = cv2.FONT_HERSHEY_DUPLEX, fontScale = 3, 
                    color = (0, 255, 0))
    #print(int(frameWidth/2 - 20),int(frameHeight/2))
    #print('Found ' + str(len(faces)) + ' face(s)')

if cv2.waitKey(1) & 0xFF == ord('q'):
    break

# When everything is done, release the capture
video_capture.release()
cv2.destroyAllWindows()

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您正在

putText

之前调用

imshow

，因此您将永远看不到

putText

的结果。将

imshow

语句移动到

waitKey

您正在调用

imshow

的

putText

之前的行，这样您将永远看不到

putText

的结果。将

imshow

语句移动到

waitKey

之前的行