Bayer dithering in Python. Useful for Playdate development...

dither.py

#!/usr/bin/env python3

import argparse
import pathlib

import numpy as np
from PIL import Image

bayer2x2 = 1/4 * np.array([
    [0, 2],
    [3, 1],
])

bayer4x4 = 1/16 * np.array([
    [ 0,  8,  2, 10],
    [12,  4, 14,  6],
    [ 3, 11,  1,  9],
    [15,  7, 13,  5],
])

bayer8x8 = 1/64 * np.array([
    [ 0, 32,  8, 40,  2, 34, 10, 42],
    [48, 16, 56, 24, 50, 18, 58, 26],
    [12, 44,  4, 36, 14, 46,  6, 38],
    [60, 28, 52, 20, 62, 30, 54, 22],
    [ 3, 35, 11, 43,  1, 33,  9, 41],
    [51, 19, 59, 27, 49, 17, 57, 25],
    [15, 47,  7, 39, 13, 45,  5, 37],
    [63, 31, 55, 23, 61, 29, 53, 21],
])

MATS = {
    "2x2": bayer2x2,
    "4x4": bayer4x4,
    "8x8": bayer8x8,
}


def dither(fname: pathlib.Path, oname: pathlib.Path, mat: np.ndarray):
    img = Image.open(fname).convert("L")
    pix = np.array(img) / 255
    h, w = pix.shape
    mh, mw = mat.shape
    tmat = np.resize(
        np.tile(mat, (int(np.ceil(h / mh)), int(np.ceil(w / mw)))),
        pix.shape,
    )
    dithered = (pix > tmat).astype(np.uint8) * 255
    Image.fromarray(dithered).save(oname)


if __name__ == "__main__":
    parser = argparse.ArgumentParser(
        prog="dither",
        description="apply ordered (Bayer) dithering to an image",
    )
    parser.add_argument(
        "filename",
        type=pathlib.Path,
    )
    parser.add_argument(
        "-o", "--out",
        help="if not specified, resulting image will have _dithered suffix",
        type=pathlib.Path,
    )
    parser.add_argument(
        "-m", "--matrix",
        choices=["2x2", "4x4", "8x8"],
        default="4x4",
    )
    args = parser.parse_args()
    fname = args.filename
    oname = args.out
    if oname is None:
        oname = fname.parent / f"{fname.stem}_dithered{fname.suffix}"
    dither(fname, oname, MATS[args.matrix])