#  -*- coding: utf-8 -*-

import os
from PIL  import *

curdir= " E:\\py\\WinPython-32bit-2.7.6.4\\study "

os.chdir(curdir)


def RGB2BlackWhite(filename):
    im=Image.open(filename)
     print  " image info, ",im.format,im.mode,im.size
    (w,h)=im.size
    R=0
    G=0
    B=0

     for x  in xrange(w):
         for y  in xrange(h):
            pos=(x,y)
            rgb=im.getpixel( pos )
            (r,g,b)=rgb
            R=R+r
            G=G+g
            B=B+b

    rate1=R*1000/(R+G+B)
    rate2=G*1000/(R+G+B)
    rate3=B*1000/(R+G+B)
    
     print  " rate: ",rate1,rate2,rate3

    
     for x  in xrange(w):
         for y  in xrange(h):
            pos=(x,y)
            rgb=im.getpixel( pos )
            (r,g,b)=rgb
            n= r*rate1/1000 + g*rate2/1000 + b*rate3/1000
             # print "n:",n
             if n>=90:
                im.putpixel( pos,(255,255,255))
             else:
                im.putpixel( pos,(0,0,0))
                
    im.save( " blackwhite.bmp ")                
      
def saveAsBmp(fname):    
    pos1=fname.rfind( ' . ')
    fname1=fname[0:pos1]
    fname1=fname1+ ' _2.bmp '
    im = Image.open(fname)
    new_im = Image.new( " RGB ", im.size)
    new_im.paste(im)
    new_im.save(fname1)          
     return fname1          
                
if  __name__== " __main__ ":
    filename=saveAsBmp( " 4.bmp ")
    RGB2BlackWhite(filename)
    
            



这里用RGB明度值来做比较，效果更好，速度更快

#计算某一点的明度

def getLightness( (r,g,b)):

   return (r*30+g*59+b*11)