Imaging libraries in active development?

[Alasdair McAndrew]

I'm investigating Python for image processing (having used Matlab, then Octave for some years).  And I'm spoiled for choice: PIL and its fork pillow, scipy.ndimage, scikits-image, mahotas, the Python interface to openCV...

However, PIL doesn't seem to be in active development.  What I want to know is - what are the current "standard" libraries for image processing in Python which are in active development?  

I have quite a few image processing student notes which I'm thinking of converting to Python, but I'd like to use the most up-to-date library.

Thanks,
Alasdair