webcam.py

import threading
import time
import cv2
import config


# Rate at which the webcam will be polled for new images.
CAPTURE_HZ = 30.0


class OpenCVCapture(object):
	def __init__(self, device_id=0):
		# Open the camera with webcam ID.
		self._camera = cv2.VideoCapture(0)
		if not self._camera.isOpened():
			self._camera.open(0)
		
		self._capture_frame = None
		self._capture_lock = threading.Lock()
		self._capture_thread = threading.Thread(target=self._grab_frames)
		self._capture_thread.daemon = True
		self._capture_thread.start()

	def _grab_frames(self):
		
		while True:
			retval, frame = self._camera.read()
			with self._capture_lock:
				self._capture_frame = None
				if retval:
					self._capture_frame = frame
			time.sleep(1.0/CAPTURE_HZ)

	def read(self):
		#Read single frame- return as OpenCv image - numpy array
		
		frame = None
		with self._capture_lock:
			frame = self._capture_frame
		
		while frame == None:
			time.sleep(0)
			with self._capture_lock:
				frame = self._capture_frame
		# for testing saving image.
		

		cv2.imwrite(config.DEBUG_IMAGE, frame)
		# Return the capture image data.
		return frame