convert image to provided palette

cccc.py

from itertools import chain
import sys
from PIL import Image

# Connler's Cool Content Canvas
COLORS = {
    0: (0, 0, 0),  # 000000
    1: (34, 34, 34),  # 222222
    2: (85, 85, 85),  # 555555
    3: (136, 136, 136),  # 888888
    4: (205, 205, 205),  # cdcdcd
    5: (255, 255, 255),  # ffffff
    6: (255, 213, 188),  # ffd5bc
    7: (255, 183, 131),  # ffb783
    8: (182, 109, 61),  # b66d3d
    9: (119, 67, 31),  # 77431f
    10: (252, 117, 16),  # fc7510
    11: (252, 168, 14),  # fca80e
    12: (253, 232, 23),  # fde817
    13: (255, 244, 145),  # fff491
    14: (190, 255, 64),  # beff40
    15: (112, 221, 19),  # 70dd13
    16: (49, 161, 23),  # 31a117
    17: (11, 95, 53),  # 0b5f35
    18: (39, 126, 108),  # 277e6c
    19: (50, 182, 159),  # 32b69f
    20: (136, 255, 243),  # 88fff3
    21: (36, 181, 254),  # 24b5fe
    22: (18, 92, 199),  # 125cc7
    23: (202, 183, 205),  # cab7cd
    24: (38, 41, 96),  # 262960
    25: (139, 47, 168),  # 8b2fa8
    26: (210, 76, 233),  # d24ce9
    27: (255, 89, 239),  # ff59ef
    28: (255, 169, 217),  # ffa9d9
    29: (255, 100, 116),  # ff6474
    30: (240, 37, 35),  # f02523
    31: (177, 18, 6),  # b11206
    32: (116, 12, 0),  # 740c00
}


def get_palette():
    palette = chain.from_iterable(COLORS.values())
    palette = list(palette)

    p_img = Image.new('P', (16, 16))
    p_img.putpalette(palette)
    return p_img


def conv_palette(im: Image) -> Image:
    *_, alpha = im.split()
    bg = Image.new('RGBA', im.size, (255, 255, 255, 255))
    bg.alpha_composite(im)
    im = bg.convert('RGB')

    p_img = get_palette()

    # im = im.quantize(256).convert('RGB')  # sometimes improves result

    im = im.quantize(palette=p_img, dither=0)

    return im, alpha


def main():
    im = Image.open(sys.argv[1]).convert('RGBA')
    im, alpha = conv_palette(im)
    im = im.convert('RGBA')
    im.putalpha(alpha)
    im.save(sys.argv[2])


if __name__ == '__main__':
    main()