OPT: optimized smoothing calculation and correct the physical dimension of the window
OPT: optimized smoothing calculation and correct the physical dimension of the window

Former-commit-id: 42d449048f3c470cbce0d44804d59bbea385811a
Former-commit-id: cf233686b801c00c10223a4e6bd4b0549e89a34f
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox