Turning an image into a sticker chart

$python make-sticker-chart.py <image_name>

import os
import sys
from PIL import Image, ImageDraw, ImageFont

WHITE = (255, 255, 255)
BLACK = (0, 0, 0)
FONT_SIZE = 20
# Number of squares in width (x-) direction.
NW = 8
image_name = sys.argv[1]

im = Image.open(image_name)
print(im.format, im.size, im.mode)

def get_coords(i, j):
    """Return coordinate as 'A1', 'A2' etc. from i, j."""
    return '{}{}'.format(chr(65+i), j+1)

def get_offset(s, draw, font):
    """Return the offset to centre string s when anchored top left."""
    ox, oy = draw.textsize(s, font)
    return ox/2, oy/2

w, h = im.size
# Determine the square size, and number of squares in height (y-) direction.
nw = NW
dw = w / nw
nh = int(h / dw)
dh = h / nh

# New images for the grid and reversed grid (backside of the image).
im_grid = Image.new('RGB', (w, h), WHITE)
im_rgrid = Image.new('RGB', (w, h), WHITE)

# Get the font object in the requested size.
font = ImageFont.truetype("Manjari-Bold.ttf", FONT_SIZE)

draw = ImageDraw.Draw(im)
draw_grid = ImageDraw.Draw(im_grid)
draw_rgrid = ImageDraw.Draw(im_rgrid)

# Draw the grid lines and coordinate labels on the images.
for i in range(nw):
    # Vertical lines.
    draw.line((i*dw, 0) + (i*dw, h), fill=WHITE)
    draw_grid.line((i*dw, 0) + (i*dw, h), fill=BLACK)
    draw_rgrid.line((w-i*dw, 0) + (w-i*dw, h), fill=BLACK)

    # Coordinate labels: centre the text in each square.
    tx = (i+0.5)*dw
    for j in range(nh):
        ty = (j+0.5)*dh
        s = get_coords(i,j)
        ox, oy = get_offset(s, draw_grid, font)
        draw_grid.text((tx-ox,ty-oy), s, fill=BLACK, font=font)
        draw_rgrid.text((w-tx-ox,ty-oy), s, fill=BLACK, font=font)

# These are the horizontal lines.
for j in range(nh):
    draw.line((0, j*dh) + (w, j*dh), fill=WHITE)
    draw_grid.line((0, j*dh) + (w, j*dh), fill=BLACK)
    draw_rgrid.line((0, j*dh) + (w, j*dh), fill=BLACK)

# Save the lot as JPEG images and bundled together as a PDF.
stem_name = os.path.splitext(image_name)[0]
im.save(stem_name + '_gridded.jpg')
im_grid.save(stem_name + '_grid.jpg')
im_rgrid.save(stem_name + '_rgrid.jpg')

images = [im, im_rgrid, im_grid]
pdf_name = stem_name + '.pdf'
images[0].save(pdf_name, save_all=True, append_images=images[1:])