automatic brightness adjustment on external monitor

auto_brightness.py

import cv
import commands
import time
from PIL import Image
from collections import deque

camera = cv.CreateCameraCapture(-1)

prev_brightness_values = deque([], 5)
prev_brighness = None

def mean(collection):
    return float(sum(collection)) / len(collection)

while 1:
    frame = cv.QueryFrame(camera)

    pi = Image.fromstring("L", cv.GetSize(frame), frame.tostring())
    pi.thumbnail((32, 24, ))
    image = [ord(i) for i in pi.tostring()]
    brightness = mean(image) / 256.0 * 100.0
    prev_brightness_values.append(brightness)
    brightness = int(mean(prev_brightness_values))
    if brightness != prev_brighness:
        cmd = "ddccontrol -p -r 0x10 -w %d" % brightness
        status, output = commands.getstatusoutput(cmd)
        assert status is 0
        print("set brightness to %s" % brightness)
    else:
        print("keeping brightness at %s" % brightness)
    prev_brighness = brightness

    time.sleep(5)