我正在尝试用Raspberry Pi相机构建一个简单的监控程序，使用OpenCV进行人脸检测 . 这是我的代码：

# -*- coding: utf-8 -*- 
from picamera.array import PiRGBArray
from picamera import PiCamera
import time
import cv2

#setting up the camera 
camera = PiCamera()
camera.resolution = (320, 240)
camera.framerate = 30
rawCapture = PiRGBArray(camera, size=(320, 240))

#basic cascade classifier
face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
#0.1 sec warmup 
time.sleep(0.1)

# capture frames from the camera
for frame in camera.capture_continuous(rawCapture, format="bgr", use_video_port=True):  
    image = frame.array
    gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
    faces = face_cascade.detectMultiScale(gray, 1.3, 5)

    #rectangle  loop
    for(x, y, w, h) in faces:
        image = cv2.rectangle(image,(x, y), (x+w, y+h), (255, 0, 0), 2)

    # show the frame [here comes the problem]
    cv2.imshow("Frame", image)
    #   cv2.imshow("Gray", gray
    key = cv2.waitKey(100) & 0xFF

# clear the stream in preparation for the next frame
rawCapture.truncate(0)
# if the `q` key was pressed, break from the loop
if key == ord("q"):
    break

关键是，当我在图像中绘制矩形时，它会出现此错误：

OpenCV错误：imshow中的断言失败（size.width> 0 && size.height> 0），文件/home/pi/opencv-2.4.10/modules/highgui/src/window.cpp，第261行Traceback（最新版本）最后调用）：文件“camera2.py”，第36行，cv2.imshow（“Frame”，image）cv2.error：/home/pi/opencv-2.4.10/modules/highgui/src/window.cpp： 261：错误：（-215）size.width> 0 && size.height> 0 in function imshow

如果我把cv2.imshow放在矩形循环之前，它就可以完美地运行 . 此外，打印faces对象显示detectMultiScale实际上正在识别面 . 我该怎么办？

谢谢 .

python opencv raspberry-pi