python - 无休止地打开和关闭网络摄像头？

Question

我编写了一个代码，该代码将最终捕获图片，并在达到一定时间后终止。
但是一旦脚本结束(即在使用时间终止代码之后)，几秒钟后我将如何自动重新运行？

import cv2
import time
import numpy

capture = cv2.VideoCapture(0)
capture.set(3,640)
capture.set(4,480)
img_counter = 0
frame_set = []
start_time = time.time()

while(True):
    ret , frame = capture.read()
    gray = cv2.cvtColor(frame,cv2.COLOR_BGR2GRAY)
    frame_set.append(gray)
    cv2.imshow('frame',gray)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
    end_time = time.time()
    elapsed = end_time - start_time
    img_name = "opencv_frame_{}.png".format(img_counter)
    cv2.imwrite(img_name,gray)
    print("{} written!".format(img_counter))
    img_counter +=1
    if elapsed > 1:
        break
capture.release()
cv2.destroyAllWindows()

此代码会将图像保存到文件夹中，并在几秒钟后终止。几分钟后如何设置自动重新运行代码以再次捕获更多图像？

谢谢是提前。

Answer 1

如果您在Windows上，则可以在Task Scheduler中添加.py脚本，并给它运行时间described here:

但是，如果要在python文件中执行此操作，则有几种方法。

第一种方法:

锁定计时器，而不是break退出循环。

就像是:

import time
starttime=time.time()
while True:
  print("tick every 3 seconds")
  time.sleep(3)

因此，您的代码应为:

import cv2
import time
import numpy

capture = cv2.VideoCapture(0)
capture.set(3,640)
capture.set(4,480)
img_counter = 0
frame_set = []
start_time = time.time()

while(True):
ret , frame = capture.read()
gray = cv2.cvtColor(frame,cv2.COLOR_BGR2GRAY)
frame_set.append(gray)
cv2.imshow('frame',gray)
if cv2.waitKey(1) & 0xFF == ord('q'):
    break
end_time = time.time()
elapsed = end_time - start_time
img_name = "opencv_frame_{}.png".format(img_counter)
cv2.imwrite(img_name,gray)
print("{} written!".format(img_counter))
img_counter +=1
if elapsed > 1:            
   capture.release()
   cv2.destroyAllWindows()
   time.sleep(3)

第二种方法:

使用Twisted, which is an event-driven networking engine written in Python.，

from twisted.internet import task, reactor

timeout = 60.0 # Sixty seconds

def doWork():
    #do work here
    pass

l = task.LoopingCall(doWork)
l.start(timeout) # call every sixty seconds

reactor.run()

在这种情况下，您不需要时间锁定:

from twisted.internet import task, reactor
import cv2
import time
import numpy

capture = cv2.VideoCapture(0)
capture.set(3,640)
capture.set(4,480)
img_counter = 0
frame_set = []
start_time = time.time()

timeout = 60.0 # Sixty seconds

def doWork():
    while (True):
        ret, frame = capture.read()
        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
        frame_set.append(gray)
        cv2.imshow('frame', gray)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
        end_time = time.time()
        elapsed = end_time - start_time
        img_name = "opencv_frame_{}.png".format(img_counter)
        cv2.imwrite(img_name, gray)
        print("{} written!".format(img_counter))
        img_counter += 1
        if elapsed > 1:
            break
    capture.release()
    cv2.destroyAllWindows())

l = task.LoopingCall(doWork)
l.start(timeout) # call every sixty seconds

reactor.run()

Note: Since your are capturing pictures and will terminating the script after it reaches a certain time, you need to sync the timeout in this case with your elapsed time to make sure it does not collide. i.e. if the script is capturing pictures for 5 minutes then the timeout should be greater than that. In other words, Run the script after uhm, let's say 7 minutes and it will take 5 minutes for capturing the pictures.