opencv_logitech_exposure.py

#!/usr/bin/env python

import cv2
from sys import argv, exit
import subprocess


def set_exposure(device,exposure):
	'''
	Sets the exposure values for Logitech C250 camera
	@device: device name string (Ex: /dev/video0)
	@exposure: valid exposure value [3,2047]. 0 for auto exposure
	
	Returns:
	0 - failure
	1 - success
	'''
	print "Setting exposure {} on camaera {}".format(exposure,device)
	# This doesn't work on Logitech Cameras
	# cap.set(cv2.CAP_PROP_EXPOSURE,float(exposure))
	if int(exposure) == 0:
		#Set to auto exposure
		try:
			print "Setting auto exposure"
			_out=subprocess.check_call(["v4l2-ctl -d {} --set-ctrl=exposure_auto=3".format(device)],shell=True)
		except subprocess.CalledProcessError:
			print "Could not set to auto exposure"
			return 0
		else:
			print "Debug: {}".format(_out)
			return 1
	else:
		try:
			_out=subprocess.check_output(["v4l2-ctl -d {} --set-ctrl=exposure_absolute={}".format(device,exposure)],shell=True)
			print "Debug: {}".format(_out)
		except subprocess.CalledProcessError:
			print "Couldn't set Exposure Manually. Trying to set camera to manual exposure mode"
			try:
				_out=subprocess.check_output(["v4l2-ctl -d {} --set-ctrl=exposure_auto=1".format(device)],shell=True)
				print "Debug: {}".format(_out)
				_out=subprocess.check_output(["v4l2-ctl -d {} --set-ctrl=exposure_absolute={}".format(device,exposure)],shell=True)
				print "Debug: {}".format(_out)
			except subprocess.CalledProcessError:
				print "Could not set exposure."
				return 0
			else:
				return 1
		else:
			return 1


if __name__ == '__main__':
	if len(argv) != 3:
		print "Usage: {} <camera> <exposure>".format(argv[0])
		exit(1)

	device=argv[1]
	exposure=argv[2]
	
	# Set device exposure
	if not set_exposure(device,exposure):
		print "Failed to set exposure"
		exit(1)
	
	print "Opening device: {}".format(device)
	cap = cv2.VideoCapture(device)
	if not cap.isOpened():
		print "Unable to open the camera"
		exit(1)
	cv2.namedWindow('Image')
	cv2.moveWindow('Image',100,100)

	print "Showing image; Press q to exit"
	while (True):
		_,c = cap.read()
		cv2.imshow('Image',c)
		q=cv2.waitKey(30)
		if q == ord('q'):
			break

	print "Exit"
	cap.release()
	cv2.destroyAllWindows()

For Auto Exposure

		_out=subprocess.check_output(["v4l2-ctl -d {} --set-ctrl=exposure_auto=3".format(device)],shell=True)