#!/usr/bin/python
"recipes mostly from http://www.pythonware.com/library/pil/handbook/image.htm"
import sys, os, random
from PIL import Image
DEBUGGING = True
def bw(sourcefile, savefile):
 "convert to black-and-white rendition of same image"
 image = Image.open(sourcefile)
 bw = image.convert('L')
 bw.save(savefile, image.format)
 return bw
def crosseyed(sourcefile, savefile):
 "convert black-and-white image to double image that must be viewed crosseyed"
 image = Image.open(sourcefile)
 if image.mode != 'L':
  debug('converting mode %s to L (black and white)' % image.mode)
  image = bw(sourcefile, '/tmp/bw.tmp')
 image.thumbnail((160, 320))  # no more than 160 pixels wide
 width, height = image.size
 crossed = Image.new('L', (width << 1, height), None)
 sourcedata = list(image.getdata())
 white = max(sourcedata)
 destdata = []
 for i in range(height):
  index = width * i
  split = randsplit(sourcedata[index:index + width], white)
  if i < 5 or i > height - 5:
   for j in range(4):  # black boxes help eye align images into one
    split[0][j] = 0
    split[1][j] = 0
  destdata += split[0] + split[1]
 crossed.putdata(destdata)
 crossed.save(savefile, image.format)
def randsplit(pixels, white):
 pixmap = map(None, range(len(pixels)), pixels)
 #debug(pixmap)
 remove = dict(random.sample(pixmap, int(len(pixels) / 2)))
 result = (list(pixels), [white] * len(pixels))
 #debug('result: %s' % repr(result))
 for i in range(len(pixels)):
  if remove.has_key(i):
   result[1][i], result[0][i] = result[0][i], result[1][i]
 return (result[0], result[1])
def debug(message):
 if DEBUGGING:
  print >>sys.stderr, message
if __name__ == '__main__':
 crosseyed(sys.argv[1], sys.argv[2])