SIGNALIS save data decoder/encoder

signalis.py

#!/usr/bin/python
"""
signalis.py decode <input.png> <output.json>
signalis.py encode <input.json> <output.png>

the decoder does NOT validate the input image! to do that, encode data again and check image pixels match
"""

import os, sys
import numpy as np
from PIL import Image

def __main__():
	args = sys.argv[1:]
	if len(args) != 3:
		print(__doc__, file=sys.stderr)
		exit(1)

	mode, infile, outfile = args
	{ "decode": decode, "encode": encode }[mode](infile, outfile)

TEMPLATE_PATH = os.path.join(os.path.dirname(__file__), "template.png")
template = np.array(Image.open(TEMPLATE_PATH))

def decode(infile: str, outfile: str):
	image = np.array(Image.open(infile, "r", ["png"]))
	data = (template != image)[::-1, :, :3].reshape(-1, 8)
	data = bytes( sum(int(b[i]) << i for i in range(8)) for b in data )

	end = len(data)
	while end and data[end - 1] == 0: end -= 1
	data = data[:end]

	with open(outfile, "wb") as f:
		f.write(data)

def encode(infile: str, outfile: str):
	image = template.copy()
	with open(infile, "rb") as f:
		data = f.read()

	pixels = image[::-1, :, :3]
	values = pixels.reshape(-1)
	write_values(values, data)
	pixels[:] = values.reshape(pixels.shape)

	Image.fromarray(image).save(outfile, "png")

def write_values(values: np.ndarray, data: bytes):
	assert not data.endswith(b"\0")
	bits = ( (byte >> i) & 1 for byte in data for i in range(8) )

	for i, bit in enumerate(bits):
		diff = bit * 10
		if values[i] + diff > 255:
			# adding would cause an overflow; subtract instead
			diff *= -1
		values[i] += diff

if __name__ == "__main__":
	__main__()

You are a lifesaver, i cannot thank you enough.