pixel art to numeric text grid

pixelimg.py

#!/usr/bin/env python3

import sys
from PIL import Image

# opens a limited palette 
# pixel art image and outputs
# a 0-9 digit grid 
#   + palette


if __name__ == '__main__':
    fname = sys.argv[1]
    img = Image.open(fname)

    w, h = img.size
    colors = {}
    for y in range(h):
        for x in range(w):
            r,g,b,a = img.getpixel((x,y))
            col = f'{r},{g},{b}'
            if a == 0:
                print('0', end='')
            elif col in colors:
                print(colors[col], end='')
            else:
                colors[col] = len(colors) + 1
                print(colors[col], end='')

        print()
    print('\n', colors)