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Update PiVideoStream to let its method 'read' always return newly updated frame #231

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Update PiVideoStream to let its method 'read' always return newly updated frame #231

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19 changes: 15 additions & 4 deletions imutils/video/pivideostream.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
from picamera import PiCamera
from threading import Thread
import cv2
import time

class PiVideoStream:
def __init__(self, resolution=(320, 240), framerate=32, **kwargs):
Expand All @@ -22,9 +23,10 @@ def __init__(self, resolution=(320, 240), framerate=32, **kwargs):
self.stream = self.camera.capture_continuous(self.rawCapture,
format="bgr", use_video_port=True)

# initialize the frame and the variable used to indicate
# if the thread should be stopped
# initialize the frame and the checker that checks is it updated
# and the variable used to indicate if the thread should be stopped
self.frame = None
self.is_updated = False
self.stopped = False

def start(self):
Expand All @@ -38,9 +40,10 @@ def update(self):
# keep looping infinitely until the thread is stopped
for f in self.stream:
# grab the frame from the stream and clear the stream in
# preparation for the next frame
# preparation for the next frame and update the update checker
self.frame = f.array
self.rawCapture.truncate(0)
self.is_updated = True

# if the thread indicator variable is set, stop the thread
# and resource camera resources
Expand All @@ -51,9 +54,17 @@ def update(self):
return

def read(self):
# return the frame most recently read
# block until there is newly updated frame
while not self.is_updated:
if self.stopped:
return None
time.sleep(0.001)
continue
self.is_updated = False
# return the newly updated frame
return self.frame

def stop(self):
# indicate that the thread should be stopped
self.stopped = True