1. School of Engineering, Computing and Mathematics, University of Plymouth, Plymouth, UK
2. Centre for Health Technology, University of Plymouth, Plymouth, UK
3. Department of Primary Care and Public Health, School of Public Health, Imperial College London, London, UK
4. Department of Computing, Sheffield Hallam University, Sheffield, UK
5. Key Laboratory of Digital Signal and Image Processing of Guandong Province, Shantou University, Shantou, China