Phillips CD-i rule 90 demonstration

cdi90.py

# this program generates the "rule 90" fill bitstream
# seen at the start of many Phillips CD-i disc images

import PIL.Image

filename = "cdi90.png"
width = 29
height = 645

# first valid parent row starts at bit 188
seed = [0,0,0,0,0,0,0,0,1,0,1,0,1,0,1,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1]

# rule 90
rule = [[1,1,0],[0,1,1],[0,0,1],[1,0,0]]

img = PIL.Image.new('1',(width,height),color=0)

# draw seed row
for i in range(width):
    p = len(seed)-width
    img.putpixel((i,0),1-seed[p+i])

# generate subsequent bits
for i in range(width*(height-1)):
    p = len(seed)-width-1
    parents = seed[p:p+3]
    c = 1 if parents in rule else 0
    seed = seed[1:] + [c]
    x = i % width
    y = 1 + (i // width)
    img.putpixel((x,y),1-c)

img.save(filename)