Dim image from one folder and put it in another, for each new image

dimmer.py

#!/usr/bin/env python3
import numpy as np
import cv2
import time
import os

DIM = 0.5
ROOTDIR = "/home/tano/Dropbox/earth"
SAVEDIR = "/home/tano/Dropbox/earth/dimmed"

if __name__ == "__main__":
  # get initial list of file
  files = os.listdir(ROOTDIR)
  files = [f for f in files if os.path.isfile(os.path.join(ROOTDIR, f))]

  # check every time there is a new image in the image folder, and dim it
  while True:
    # check images
    new_files = os.listdir(ROOTDIR)
    new_files = [f for f in new_files if os.path.isfile(
        os.path.join(ROOTDIR, f))]

    # print(len(files), len(new_files))

    if len(files) < len(new_files):
      # check newest image
      for fname in new_files:
        if not fname in files:
          # open the image
          img = cv2.imread(os.path.join(ROOTDIR, fname))
          print(img.max())
          print(img.min())
          if img is not None:
            print("Saving img {} in dimmed".format(fname))
            # dim it
            img = img.astype(np.float32) * DIM
            print(img.max())
            print(img.min())
            img = img.astype(np.uint8)
            print(img.max())
            print(img.min())
            # save it
            cv2.imwrite(os.path.join(SAVEDIR, fname), img)

    files = new_files

    # sleep for a couple of seconds
    time.sleep(1)