OPT: modified test of non local mean filter
OPT: modified test of non local mean filter

Former-commit-id: 1a0bb930704209747f514939a219a84b1a6c8083 [formerly f80998d72110e7a7631f3c1a6fd3b1764640f9a4]
Former-commit-id: 5135c788f7bf5efca076562bd9ae312dff90974b
Former-commit-id: ac4672fa268b3e57429ffec5a52c863c395e6fcb
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox