python 转换彩图为黑白图 ，去噪

# -*- 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>=60:
                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("2ujb.bmp")
    RGB2BlackWhite(filename)