Pillow PNG artifacts

artifacts.py

#!/usr/bin/python
# -*- coding: utf-8 -*-

# This script reproduces the issue with artifacts when
# handling (semi)transparent PNG files:
# https://github.com/python-pillow/Pillow/issues/1449


# Version used:
#
# Python 2.7.10 (default, Jul 14 2015, 19:46:27)
# [GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.39)] on darwin
#
# PILLOW_VERSION:  3.0.0
#

#
# Setup:
#   pip install pillow
#

from PIL import Image
from PIL import PILLOW_VERSION

def main():
    im = Image.open("original.png")
    # <PIL.PngImagePlugin.PngImageFile image mode=LA size=1820x672 at 0x10855F550>
    im.thumbnail((259, 96))
    im.save("thumbnail.png")
    print "PILLOW_VERSION: ", PILLOW_VERSION

if __name__ == "__main__":
    main()

original.png

thumbnail.png