Extract image channels into sperate grayscale image

dumpic.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
from __future__ import print_function

from PIL import Image
import re

def main():
    import sys
    for filename in sys.argv[1:]:
        items = Image.open(filename).split()
        names = ('r', 'g', 'b', 'a')
        for n in range(len(items)):
            channel = items[n]
            savename = re.sub(r'(\.[^.]+)$', r'_{}\g<1>'.format(names[n]), filename)
            channel.save(savename)
            print('>>> {}'.format(savename))


if __name__ == '__main__':
    main()