custom flipnote thumbnail tool

thumbtool.py

# Custom Flipnote (.ppm) Thumbnail Tool
# Create a ppm thumbnail from any 64 x 48 image
# Requires Pillow - https://github.com/python-pillow/Pillow
# 
# By Jaames <github.com/jaames | @rakujira on twitter>
# 
# Usage: python3 thumbtool.py input.ppm thumb.png

from PIL import Image
from sys import argv

# thumbnail palette
palette = [
  0xFF, 0xFF, 0xFF,
  0x52, 0x52, 0x52,
  0xFF, 0xFF, 0xFF,
  0x9C, 0x9C, 0x9C,
  0xFF, 0x48, 0x44,
  0xC8, 0x51, 0x4F,
  0xFF, 0xAD, 0xAC,
  0x00, 0xFF, 0x00,
  0x48, 0x40, 0xFF,
  0x51, 0x4F, 0xB8,
  0xAD, 0xAB, 0xFF,
  0x00, 0xFF, 0x00,
  0xB6, 0x57, 0xB7,
  0x00, 0xFF, 0x00,
  0x00, 0xFF, 0x00,
  0x00, 0xFF, 0x00,
]

# create lookup image for the palette
palimg = Image.new("P", (16, 16))
palimg.putpalette(palette * 16)

# open thumb image
img = Image.open(argv[2])
img = img.convert("RGB")
# apply palette
# https://stackoverflow.com/questions/29433243/convert-image-to-specific-palette-using-pil-without-dithering/29438149
img.load()
palimg.load()
im = img.im.convert("P", 0, palimg.im)
img = img._new(im)

# open donor ppm
with open(argv[1], "rb+") as ppm:
  # seek to the start of the thumbnail data
  ppm.seek(160)

  # convert image into 8*8 tiled 4-bit bitmap and write to ppm
  for tileIndex in range(0, 48):
    tileX = tileIndex % 8 * 8
    tileY = tileIndex // 8 * 8
    for line in range(0, 8):
      for pixel in range(0, 8, 2):
        x = tileX + pixel
        y = tileY + line
        # each byte is comprised of 2 pixels
        pix1 = img.getpixel((x, y)) % 16
        pix2 = img.getpixel((x + 1, y)) % 16
        ppm.write(bytes([pix1 | (pix2 << 4)]))