Comparison of Different Approaches With Different Evaluation Metrics, Where N/A Indicates That the Corresponding Result was Not Reported in the Respective Paper. The Best Results Across Different Methods are Bolded. The Last Four Rows Show the Results Obtained by the Proposed Method by Using 1) Only the Discriminative Patch Based Representation (DisPatch), 2) the Discriminative Patch Based Representation With Sparse Coding (S + DisPatch), 3) the Discriminative Patch Based Representation With Sparse Coding and Hierarchical Labeling Strategy (HS + DisPatch), and 4) the Proposed Method by Further Adopting the Online Update Mechanism, Respectively