arnold_cat.py

from PIL import Image, ImageChops
import sys

img = Image.open(sys.argv[1]).convert("RGB")
w, h = img.size
out = Image.new("RGB", (w, h))

def f(x, y):
    return ((2*x+y) % w, (x+y) % h)

img.save("frames/0.png")
orig = img

# """
limit = sys.maxsize+1
"""
limit = int(sys.argv[2])+1
# """

for n in range(1, limit):
    for i in range(w):
        for j in range(h):
            out.putpixel(f(i, j), img.getpixel((i, j)))

    if ImageChops.difference(orig, out).getbbox() is None:
        break

    out.save("frames/"+str(n)+".png")
    img = out
    out = Image.new("RGB", (w, h))