extract data embeded in pixel channels

extract.py

from PIL import Image
import argparse
from collections import OrderedDict

def parseMask(string):
	mask = []
	for val in string.split(","):
		if "-" in val: 
			min, max = val.split("-")
			mask += [1 << (i - 1) for i in range(int(min), int(max) + 1)]
		else:
			mask += [1 << (int(val) - 1)]
	mask.sort()
	return mask

parser = argparse.ArgumentParser(prog='extract.py', 
	usage='%(prog)s [options] image',
	formatter_class=argparse.RawTextHelpFormatter,
	epilog="PLANE = comma separated values or a range. example: 1,2,5 or 1-5\n" +
	"ORDER = any combination of r/g/b/a. example: rgba, abrg, brg")

parser.add_argument("image", help="path to image")
parser.add_argument("-r", dest="r", help="bit plane of red channel", metavar="PLANE", default=False, type=parseMask)
parser.add_argument("-g", dest="g", help="bit plane of green channel", metavar="PLANE", default=False, type=parseMask)
parser.add_argument("-b", dest="b", help="bit plane of blue channel", metavar="PLANE", default=False, type=parseMask)
parser.add_argument("-a", dest="a", help="bit plane of alpha channel", metavar="PLANE", default=False, type=parseMask)
parser.add_argument("-c", dest="channel", help="order of channel (default: rgba)", metavar="ORDER", default=False)
parser.add_argument("-l", dest="limit", help="limit output to N character", metavar="N", default=0, type=int)
parser.add_argument("-o", dest="order", help="pixel iteration order (default: row)", default="row", choices=["row", "column"], type=str.lower)
parser.add_argument("-B", dest="bit", help="bit order to process (default: lsb)", default="lsb", choices=["lsb", "msb"], type=str.lower)
args = vars( parser.parse_args() )

img = Image.open(args["image"])
if args["order"] == "row": column, row = img.size
else: row, column = img.size
stream = ""
done = False
pixel = OrderedDict()

if args["channel"] == False: 
	args["channel"] = "rgba" if img.mode == "RGBA" else "rgb"

for channel in list("rgba"):
	pixel[channel] = 0xff
	# if bit == msb, reverse the mask order
	if args["bit"] == "msb" and args[channel] != False:
		args[channel] = args[channel][::-1]

for y in range(row):
	if done: break
	for x in range(column):
		if done: break
		order = (x, y) if args["order"] == "row" else (y, x)
		for index, value in enumerate( img.getpixel(order) ):
			pixel[pixel.keys()[index]] = value
		# loop based on rgba order
		for channel in list(args["channel"]):
			if done: break
			# if bit plane(s) is defined
			if args[channel] != False:
				for mask in args[channel]:
					if done: break
					val = pixel[channel] & mask
					stream += "1" if val == mask else "0"
					# if limit is reached, stop processing
					if len(stream) / 8.0 == int(args["limit"]):
						done = True

# convert binary stream to ascii
print ''.join( chr( int(stream[i:i+8], 2) ) for i in range(0, len(stream), 8) )