Revisiting Performance Measures for Cross-Modal Hashing

Recently, cross-modal hashing has attracted much attention due to its low storage cost and fast query speed. Mean Average Precision (MAP) is the most widely used performance measure for cross-modal hashing. However, we found that the MAP scores do not fully reflect the quality of the top-K results for cross-modal retrieval because it neglects multi-label information and overlooks the label semantic hierarchy. In view of this, we propose a new performance measure named Normalized Weighted Discounted Cumulative Gains (NWDCG) by extending Normalized Discounted Cumulative Gains (NDCG) using co-occurrence probability matrix. To verify the effectiveness of NWDCG, we conduct extensive experiments using three popular cross-modal hashing schemes over two publically available datasets.