Python opencv和多处理

Question

我希望使用python的多处理模块创建一个进程,通过opencv的python接口连续轮询网络摄像头,将任何结果图像发送到队列,其他进程可以从中访问它们.但是,每当我尝试对队列中其他进程检索到的图像做任何事情时,我都会遇到挂起(Ubuntu 12.04上的python 2.7).这是一个最小的例子:

import multiprocessing
import cv

queue_from_cam = multiprocessing.Queue()

def cam_loop(queue_from_cam):
    print 'initializing cam'
    cam = cv.CaptureFromCAM(-1)
    print 'querying frame'
    img = cv.QueryFrame(cam)
    print 'queueing image'
    queue_from_cam.put(img)
    print 'cam_loop done'


cam_process = multiprocessing.Process(target=cam_loop,args=(queue_from_cam,))
cam_process.start()

while queue_from_cam.empty():
    pass

print 'getting image'
from_queue = queue_from_cam.get()
print 'saving image'
cv.SaveImage('temp.png',from_queue)
print 'image saved'

此代码应该运行到"保存图像"的打印,但然后挂起.我有什么想法可以解决这个问题吗？

Answer 1

最简单的方法是使用cv2基于NumPy数组的较新模块.这样你就不必乱用手工酸洗.这是修复(我只更改了4行代码):

import multiprocessing
import cv2

queue_from_cam = multiprocessing.Queue()

def cam_loop(queue_from_cam):
    print 'initializing cam'
    cap = cv2.VideoCapture(0)
    print 'querying frame'
    hello, img = cap.read()
    print 'queueing image'
    queue_from_cam.put(img)
    print 'cam_loop done'

cam_process = multiprocessing.Process(target=cam_loop,args=(queue_from_cam,))
cam_process.start()

while queue_from_cam.empty():
    pass

print 'getting image'
from_queue = queue_from_cam.get()
print 'saving image'
cv2.imwrite('temp.png', from_queue)
print 'image saved'

Answer 2

看来解决方案是将 opencv iplimage 对象转换为字符串，然后在将其添加到队列之前对其进行腌制：

import multiprocessing
import cv
import Image
import pickle
import time

queue_from_cam = multiprocessing.Queue()

def cam_loop(queue_from_cam):
    print 'initializing cam'
    cam = cv.CaptureFromCAM(-1)
    print 'querying frame'
    img = cv.QueryFrame(cam)
    print 'converting image'
    pimg = img.tostring()
    print 'pickling image'
    pimg2 = pickle.dumps(pimg,-1)
    print 'queueing image'
    queue_from_cam.put([pimg2,cv.GetSize(img)])
    print 'cam_loop done'


cam_process = multiprocessing.Process(target=cam_loop,args=(queue_from_cam,))
cam_process.start()

while queue_from_cam.empty():
    pass

print 'getting pickled image'
from_queue = queue_from_cam.get()
print 'unpickling image'
pimg = pickle.loads(from_queue[0])
print 'unconverting image'
cv_im = cv.CreateImageHeader(from_queue[1], cv.IPL_DEPTH_8U, 3)
cv.SetData(cv_im, pimg)
print 'saving image'
cv.SaveImage('temp.png',cv_im)
print 'image saved'