scikit-image 0.15.0 is out: https://github.com/scikit-image/scikit-image/blob/master/doc/release/release_0.15.rst version 0.13.0 currently in portage is old and is incompatible with the current version of numpy, see this bug: https://bugs.gentoo.org/683196
fixed, newer version is now present in the tree https://gitweb.gentoo.org/repo/gentoo.git/tree/sci-libs/scikit-image