Sorry, I think the +1 should go in `slic_superpixels.py` if `enforce_connectivity` is `False`. This makes this code less readable (you'd need to write `k + 1` for PEP8, btw ;), and is actually slower: you're doing +1 and -1 on each pixel *and* each iteration, instead of just doing +1 on each pixel at the end! At any rate, maybe let the core devs hash out whether we want +1 or not. If not, instead of this we'll have to modify `_enforce_label_connectivity_cython` to start from 0. (Could be done by initialising the array to -1.)