全局变量的错误没有在python的线程函数中定义 [英] Error with global variables are not defined in a thread function on python
问题描述
我正在使用网络摄像头开展OCR项目。我定义了一个 capture()
函数,用于保存帧,其中包含最少20个等值线,面积大于60像素,等待3秒。我需要主循环一直工作。所以我使用一个线程来调用 capture()
函数。当我运行代码时,Python Shell返回一个错误: NameError:全局名称框架,ln2未定义。第13条注释行解决了变量框架的错误。这是否意味着我必须复制while循环中的所有代码?
我在Windows 7上使用python 2.7。
以下是代码:
进口cv2
进口时间
进口线程
cap = cv2.VideoCapture(0)
def capture():
全局框架,ln2
if ln2> 20:
cv2.imwrite(frame.jpg,frame)
time.sleep(3)
#ret,frame = cap.read()#it解决了
child_t = threading.Thread(target = capture)
child_t.setDaemon(True)
child_t.start()
$ b $ (1):
a = []
ret,frame = cap.read()
img1 = cv2.cvtColor(frame,cv2.COLOR_BGR2GRAY)
_,img2 = cv2.threshold(img1,127,255,cv2.THRESH_BINARY)
(_,contornos,_)= cv2.findContours(img2,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)
ln = len(contornos)
在范围内(0,ln):
cn = contornos [i]
x,y,w,h = cv2.boundingRect(cn)
area = 2 *(w + h)
if area> 60和面积< 1000:
cv2.rectangle(frame,(x,y),(x + w,y + h),(0,255,0),2)
a.append(area)
ln2 = len(a)
print ln2
#我想调用capture()函数
cv2.imshow('Webcam ',frame)
if cv2.waitKey(1)& 0xFF == ord('x'):
break
$ b child_t.join()
cap.release()
cv2.destroyAllWindows()
请注意,我正在使用 threading.Timer
,而不是 threading.Thread
后跟一个时间。睡眠
。 另外,你说你需要保存包含最少20个等值线的面积大于60像素的帧,但相关的如果代码中的
语句没有这样做。所以我也添加了。
消息 NameError:全局名称框架,ln2未定义是因为线程甚至开始在读取 frame
之前。同样适用于变量 ln2
。这在下面的代码中也是固定的。基本上我用 writeToFile
来解决这个问题。
import threading
import cv2
$ b $ writeToFile = False
exitTask = False
$ b $ def threadTask():
全局框架
如果不是exitTask :
threading.Timer(3.0,threadTask).start()
if writeToFile:
cv2.imwrite(Threads.jpg,frame)
print写入文件
cap = cv2.VideoCapture(0)
threadTask()
while(True):
areasList = []
try:
ret,frame = cap.read()
img1 = cv2.cvtColor(frame,cv2.COLOR_BGR2GRAY)
_,img2 = cv2 .threshold(img1,127,255,cv2.THRESH_BINARY)
(_,contour,_)= cv2.findContours(img2,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)
nContours = len(contour)
为轮廓轮廓:
x,y,w,h = cv2.boundingRect(轮廓)
面积= 2 *(w + h)
#if区域> 60和面积<如果(nContours> 10)和(area> 20):
cv2.rectangle(frame,(x,y),(x + w,y + h),(0, 255,0),2)
areasList.append(area)
writeToFile = True
else:
writeToFile = False
#print len(areasList )
cv2.imshow('Webcam',frame)
if cv2.waitKey(1)& 0xFF == ord('x'):
举起KeyboardInterrupt
,除了KeyboardInterrupt:
exitTask = True
cap.release()
cv2.destroyAllWindows ()
exit(0)
I'm working in a project with OCR using a webcam. I defined a capture()
function for save the frame that contains minimum 20 contours with areas greater than 60 pixels in lapses of 3 seconds. I need that the main while cycle works all the time. So I'm using a thread to call capture()
function. When I run the code the Python Shell returned an error: NameError: global name frame, ln2 are not defined. The 13th commented line solves the error for the variable frame. Does it means that I have to replicate all the code that is inside the while cycle?
I'm using python 2.7 on Windows 7.
Here is the code:
import cv2
import time
import threading
cap = cv2.VideoCapture(0)
def capture():
global frame, ln2
if ln2 > 20:
cv2.imwrite("frame.jpg", frame)
time.sleep(3)
#ret, frame = cap.read() #it solves the error for variable 'frame'
child_t = threading.Thread(target = capture)
child_t.setDaemon(True)
child_t.start()
while(1):
a = []
ret, frame = cap.read()
img1 = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
_, img2 = cv2.threshold(img1, 127, 255, cv2.THRESH_BINARY)
(_, contornos, _) = cv2.findContours(img2, cv2.RETR_LIST, cv2.CHAIN_APPROX_SIMPLE)
ln = len(contornos)
for i in range (0, ln):
cn = contornos[i]
x, y, w, h = cv2.boundingRect(cn)
area = 2*(w+h)
if area > 60 and area < 1000:
cv2.rectangle(frame, (x,y), (x+w, y+h), (0, 255, 0), 2)
a.append(area)
ln2 = len(a)
print ln2
#here I want to call capture() function
cv2.imshow('Webcam', frame)
if cv2.waitKey(1) & 0xFF == ord('x'):
break
child_t.join()
cap.release()
cv2.destroyAllWindows()
Here you go. Note that I'm using threading.Timer
instead of threading.Thread
followed by a time.sleep
.
Also, You said you need to save the frame that contains minimum 20 contours with areas greater than 60 pixels, but the related if
statement in your code doesn't do that. So I've added that as well.
The message NameError: global name frame, ln2 are not defined is because the thread is started even before frame
is being read. Same applies to the variable ln2
as well. This is also fixed in the code below. Basically I used the flag writeToFile
to overcome this issue.
import threading
import cv2
writeToFile = False
exitTask = False
def threadTask():
global frame
if not exitTask:
threading.Timer(3.0, threadTask).start()
if writeToFile:
cv2.imwrite("Threads.jpg", frame)
print "Wrote to file"
cap = cv2.VideoCapture(0)
threadTask()
while(True):
areasList = []
try:
ret, frame = cap.read()
img1 = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
_, img2 = cv2.threshold(img1, 127, 255, cv2.THRESH_BINARY)
(_, contours, _) = cv2.findContours(img2, cv2.RETR_LIST, cv2.CHAIN_APPROX_SIMPLE)
nContours = len(contours)
for contour in contours:
x, y, w, h = cv2.boundingRect(contour)
area = 2*(w+h)
#if area > 60 and area < 1000:
if (nContours > 10) and (area > 20):
cv2.rectangle(frame, (x,y), (x+w, y+h), (0, 255, 0), 2)
areasList.append(area)
writeToFile = True
else:
writeToFile = False
#print len(areasList)
cv2.imshow('Webcam', frame)
if cv2.waitKey(1) & 0xFF == ord('x'):
raise KeyboardInterrupt
except KeyboardInterrupt:
exitTask = True
cap.release()
cv2.destroyAllWindows()
exit(0)
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