#!/usr/bin/env python
#-*- encoding: utf-8 -*-
#
# deriv_image.py
# Compute the derivative of an image.
#
# Copyright (c) 2008 Pierre "delroth" Bourdon <root@delroth.is-a-geek.org>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import sys
try:
    from PIL import Image, ImageFilter, ImageChops, ImageOps, ImageEnhance
except ImportError:
    print """To use this script, you must install the Python Imaging Library
    module, also known as PIL."""
    sys.exit(1)

mat = [
         0, -1,  0,
        -1,  2,  0,
         0,  0,  0
      ]

def main():
    if len(sys.argv) != 4:
        print "Usage: %s <input-image> <output-image> <passes>" % sys.argv[0]
        return 1
    inp, out, passes = sys.argv[1:]
    im = Image.open(inp)

    for i in xrange(int(passes)):
        print "Pass", i
        im2 = im.filter(ImageFilter.Kernel((3, 3), mat, 1.0/3.0))
        im3 = ImageChops.screen(im, im2)
        im = im3.filter(ImageFilter.SMOOTH)
    im3.save(out)    
    
    return 0

if __name__ == "__main__": sys.exit(main())