How can I make images so that appengine doesn't make transparent into black on resize?

Question

I'm on the google appengine, and trying to resize images. I do :

from google.appengine.api import images
image = images.resize(contents, w, h)

And for some images I get a nice transparent resize, and others I get a black background.

How can I keep the transparency for all images?

• Original : http://www.stdicon.com/g-flat/application/pgp-encrypted
• Black : http://www.stdicon.com/g-flat/application/pgp-encrypted?size=64
• Original : http://www.stdicon.com/gartoon/application/rtf
• Black : http://www.stdicon.com/gartoon/application/rtf?size=64
• Original : http://www.stdicon.com/nuvola/application/x-debian-package
• Transparent : http://www.stdicon.com/nuvola/application/x-debian-package?size=64

Answer 1

Article on this problem: http://doesnotvalidate.com/2009/resizing-transparent-images-with-django-pil/ Google-code patch: http://code.google.com/p/sorl-thumbnail/issues/detail?id=56

Answer 2

Is this on the dev appserver, or in production? There's a known bug on the dev appserver that turns transparent to black when compositing, but it should run fine in production.

Answer 3

With PIL you have to convert your image in RGBA like this :

im = im.convert("RGBA")

If you want a better implementation, you can read the sorl-thumbnail code. It makes a good usage of PIL.