透明背景に黒一色なPNG文字絵文字をちょっと縮小して白フチ付けるやつ

moji_emoji_stroke.py

# Runs on Python 3.8 + Pillow
# Should run also on Python 3.7+

from pathlib import Path
from PIL import Image, ImageOps, ImageFilter


def main():
    Path('./stroked').mkdir(exist_ok=True)

    for fn in Path('.').glob('*.png'):
        strokify(fn)


def strokify(fn):
    orig = Image.open(fn)
    orig.thumbnail((120, 120), Image.BILINEAR)

    stroke = Image.new('RGB', (128, 128), (255, 255, 255))
    stroke.paste(orig, (4, 4), mask=orig)
    stroke = ImageOps.invert(stroke)
    stroke = stroke.filter(ImageFilter.MaxFilter(9)).convert('L')

    output = Image.new('RGBA', (128, 128), (255, 255, 255, 0))
    white = Image.new('RGB', (128, 128), (255, 255, 255))
    output.paste(white, mask=stroke)
    output.paste(orig, (4, 4), mask=orig)
    output.save(f'./stroked/{fn}')


main()