Remove "greyscale" prefix on functions in ``morphology.grey``. To avoid confusion (and name clashes), ``greyscale_open`` and ``greyscale_close`` were renamed ``opening`` and ``closing`` (instead of ``open`` and ``close``). As a bonus, these names match scipy.ndimage.
* medial_axis function in morphology.skeletonize
* plot_medial_axis.py example for the gallery
Compared to the skeletonize algorithm in morphology.skeletonize,
medial_axis is faster because it processes all pixel in one pass.
However, the resulting skeleton has more branches, that may be unwanted
depending on the application.
Tony S Yu