python pillow (字符画)

from PIL import Image
ascii_char = list('1 ')
def get_char(r,g,b,alpha=256):
    if alpha == 0:
        return ' '
    gray = int(0.2126 * r + 0.7152 * g + 0.0722 * b)
    unit = 256 / len(ascii_char)
    return ascii_char[int(gray//unit)]

def main():
    im = Image.open('images.jpg')
    WIDTH,HEIGHT = 80,48
    im = im.resize((WIDTH,HEIGHT))
    txt = ""
    for i in range(HEIGHT):
        for j in range(WIDTH):
            txt += get_char(*im.getpixel((j,i)))
        txt +='\n'
    fo = open("哆啦a梦.txt","w")
    fo.write(txt)
    fo.close()

main()