#!/usr/bin/env python
from numpy import *
from PIL import Image

n = 60 #square size
N = 6 #twice number of columns
M = 3 #twice number of rows

unit = zeros((2*n,2*n)); unit[:n,:n] = 255; unit[n+1:,n+1:] = 255
arr = tile(unit,(M,N)).astype(uint8)
Image.fromarray(arr).save('checkerboard.png')