from pygame import *
def subtract(img1,img2,path):
    surf1,surf2=image.load(img1),image.load(img2)
    width,height=surf1.get_size()
    surf3=Surface((width,height))
    for y in range(height):
        for x in range(width):
            color1=surf1.get_at((x,y))
            color2=surf2.get_at((x,y))
            diff=255-float(abs(color1[0]-color2[0])+abs(color1[1]-color2[1])+abs(color1[2]-color2[2]))/3
            surf3.set_at((x,y),[diff,diff,diff])
    image.save(surf3,path)