Collective Reconstructive Embeddings for Cross-Modal Hashing

In this paper, we study the problem of cross-modal retrieval by hashing-based approximate nearest neighbor search techniques. Most existing cross-modal hashing works mainly address the issue of multi-modal integration complexity using the same mapping and similarity calculation for data from different media types. Nonetheless, this may cause information loss during the mapping process due to overlooking the specifics of each individual modality. In this paper, we propose a simple yet effective cross-modal hashing approach, termed collective reconstructive embeddings (CRE), which can simultaneously solve the heterogeneity and integration complexity of multi-modal data. To address the heterogeneity challenge, we propose to process heterogeneous types of data using different modality-specific models. Specifically, we model textual data with cosine similarity-based reconstructive embedding to alleviate the data sparsity to the greatest extent, while for image data, we utilize the Euclidean distance to characterize the relationships of the projected hash codes. Meanwhile, we unify the projections of text and image to the Hamming space into a common reconstructive embedding through rigid mathematical reformulation, which not only reduces the optimization complexity significantly but also facilitates the inter-modal similarity preservation among different modalities. We further incorporate the code balance and uncorrelation criteria into the problem and devise an efficient iterative algorithm for optimization. Comprehensive experiments on four widely used multimodal benchmarks show that the proposed CRE can achieve a superior performance compared with the state of the art on several challenging cross-modal tasks.