resize.py

from PIL import Image
from multiprocessing import Pool

import glob

LIMIT = 1920

def resize(file):
  im = Image.open(file)
  (ow, oh) = im.size
  if ow >= oh and ow > LIMIT:
    out = im.resize((LIMIT, round(LIMIT * oh/ow)), Image.LANCZOS)
  elif oh >= ow and ow:
    out = im.resize((round(LIMIT * ow/oh), LIMIT), Image.LANCZOS)
  else:
    out = im
  out.save("result/" + file.split('/')[-1].split('.')[0] + ".png")
  print("resized " + file)
  
files = sorted(glob.glob("orig/*.png") + glob.glob("orig/*.PNG"))

with Pool(processes=4) as pool:
  pool.map(resize, files)