OPT: seg_graymatter improved
OPT: seg_graymatter improved

Former-commit-id: d5ee655b68a6d7fce136d06117db3c31223d22a3 [formerly 41ba42c3228d4f63c8f376bb9c3e843f5df7de2b]
Former-commit-id: 2728f4826a8ea4ff9acf4427ef9495f1af089ca9
Former-commit-id: 5d8a64708a15e36e543314668aa4395dcf0fab0d
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox