OpenCV Python：QueryFrame返回无

Question

我在 macbook 上使用 OpenCV 2.4 和 python 2.7.5。我想使用以下代码显示内置摄像头的实时流：

import cv

cv.NamedWindow("w1", cv.CV_WINDOW_AUTOSIZE)
camera_index = 0
capture = cv.CaptureFromCAM(camera_index)

def repeat():
    global capture #declare as globals since we are assigning to them now
    global camera_index
    frame = cv.QueryFrame(capture)
    print type(frame)
    #cv.ShowImage("w1", frame)
    c = cv.WaitKey(10)
while True:
    repeat()

但是，QueryFrame 似乎并不总是返回 iplimage，这是我在终端上得到的：

<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'cv2.cv.iplimage'>
<type 'NoneType'>
<type 'NoneType'>
<type 'cv2.cv.iplimage'>
<type 'NoneType'>
<type 'NoneType'>
<type 'NoneType'>
<type 'cv2.cv.iplimage'>
<type 'NoneType'>
<type 'NoneType'>
<type 'cv2.cv.iplimage'>
<type 'NoneType'>

有人知道问题出在哪里吗？

谢谢

编辑： 我注意到在我的相机打开之前需要几秒钟，所以我在进入“while”之前放了一些延迟。至于 noneType 问题，我不知道为什么我每 3 帧得到一个正确的图像..无论如何我只是通过设置一个条件来检查我们是否得到一个正确的图像来“修复”它，这里是代码：

import cv

cv.NamedWindow("w1", cv.CV_WINDOW_AUTOSIZE)
camera_index = 0
capture = cv.CaptureFromCAM(camera_index)
c = cv.WaitKey(5000)
def repeat():
    global capture #declare as globals since we are assigning to them now
    global camera_index
    frame = cv.QueryFrame(capture)

    if frame:

        cv.ShowImage("w1", frame)
    c = cv.WaitKey(10)
while True:
    repeat()

Answer 1

建议如下：

• camera_index = -1

• 删除第一帧以防万一

  firstImage = copy.deepcopy(cv.QueryFrame(capture))

分享我的代码供你参考：

import cv2 as cv
import copy
camera_index = -1 

capture = cv.CaptureFromCAM(camera_index)

isRunning = True
firstImage = copy.deepcopy(cv.QueryFrame(capture)) #drop first frame which might empty
cv.NamedWindow("Webcam",  cv.CV_WINDOW_AUTOSIZE);

def repeat():
    global capture #declare as globals since we are assigning to them now
    global camera_index
    global isRunning
    global firstImage
    currImage = cv.QueryFrame(capture) 
    cv.ShowImage("Webcam",currImage)
    c = cv.WaitKey(10)
    if(c==27):
            isRunning = False
    if (c!=-1):
            print str(c)

while isRunning:
    repeat()