mosaic.py

from PIL import Image, ImageDraw, ImageFont
import argparse
import numpy as np

list = "筑波大学情報学群情報メディア創成学類つくばだいがくじょうほうめでぃあそうせいがくるい"
parser = argparse.ArgumentParser()
parser.add_argument("src")
parser.add_argument("-f", "--font", default="FOT-SeuratPro-DB.otf")
args = parser.parse_args()

img = Image.open(args.src)
width = 80
height = int(img.height * (width / img.width) * 0.85)
img = img.resize((width, height))

size = 50
font = ImageFont.truetype(args.font, size)
char_denses = set()
for char in list:
  char_img = Image.new("RGB", (size, size), (255, 255, 255))
  char_draw = ImageDraw.Draw(char_img)
  char_draw.text((0, 0), char, (0, 0, 0), font)
  blacks = np.count_nonzero(np.asarray(char_img) == 0)
  char_denses.add((char, blacks))

char_denses = sorted(char_denses, key=lambda i: i[1])

img_array = np.asarray(img)
gray = 0.299 * img_array[:,:,2] + 0.587 * img_array[:,:,1] + 0.114 * img_array[:,:,0]
for y in range(height):
  for x in range(width):
    index = int(round(gray[y][x] / 255 * (len(char_denses) - 1)))
    print(char_denses[index][0], end="")
  print("")

mosaic-image

$ python mosaic.py <image> <font>