crop.py

import time
import subprocess
from subprocess import PIPE, STDOUT
import sys

from PIL import Image

resolution = 144
pdf_file_name = sys.argv[1]
r = subprocess.run(['gs', '-q', '-dBATCH', '-dNOPAUSE', '-sDEVICE=bbox', pdf_file_name], stdout=PIPE, stderr=STDOUT)
# grab the coordinate value
r_t = r.stdout.decode('utf-8')
val_str = r_t[r_t.find('HiResBoundingBox:'):].rstrip()
Ls = val_str.split(' ')
left, lower, right, upper = float(Ls[1]), float(Ls[2]), float(Ls[3]), float(Ls[4])
# output the png
png_file_name = pdf_file_name.replace('pdf', 'png')
r = subprocess.run(['gs', '-q', '-dBATCH', '-dNOPAUSE', '-sDEVICE=pngalpha', '-r' + str(resolution), '-sOutputFile=' + png_file_name, pdf_file_name])
# read the image from disk
ratio = resolution / 72
im = Image.open(png_file_name)
height = im.size[1]
left *= ratio
upper_new = height - lower * 2
right *= ratio
lower_new = height - upper * 2
im_new = im.crop((left, lower_new, right, upper_new))
im_new.save(png_file_name)