Auto-Adjust screen Brightness

import Image;
import cv;
import subprocess
import ImageStat
import time

camcapture = cv.CreateCameraCapture(0)
cv.SetCaptureProperty(camcapture,cv.CV_CAP_PROP_FRAME_WIDTH, 128)
cv.SetCaptureProperty(camcapture,cv.CV_CAP_PROP_FRAME_HEIGHT, 128);

if not camcapture:
        print "Error opening WebCAM"
        sys.exit(1)
while 1:
    #Determine environmental brightness.
        frame = cv.QueryFrame(camcapture)
    cv.SaveImage("./new.bmp",frame)
    im =Image.open("./new.bmp").convert('L')
    stat = ImageStat.Stat(im)
    stat = stat.mean[0]

        brightval = hex(int((255 - (stat*1.5)))) #Do the Math, Drop decimals, -> Hex.
    currentval=subprocess.Popen("setpci -s 00:02.0 F4.B",shell=True,stdout=subprocess.PIPE).stdout.read()
    if abs(int(brightval,16) - int(currentval,16)) > 30:
        print int(brightval,16)
        command = "setpci -s 00:02.0 F4.B=" + str(brightval)
        subprocess.Popen(command,shell=True)
    else:
        time.sleep(5)