Semantic Composition via Optimal Transport for Composed Image Retrieval

Given a reference image, composed image retrieval aims to search for the target image from the image gallery with a modification sentence. The complicated semantic relationships within the composed query to comprehend the preserved visual context and modified semantics pose a challenge for the researchers. Most current approaches concentrate on the global or fragmental composition to combine the multi-modal query features and bridge the distance between the query and the target. However, global-level matching tends to ignore fine-grained components that distinguish the matched instance from hard negative instances. As for the fragment-level matching, the over-sensitivity to the local noise due to the lack of explicit local labels and excessive computational demands may have a detrimental impact on performance. In this paper, we propose Semantic Composition via Optimal Transport (SCOT) for composed image retrieval to address the aforementioned issues. To optimize the computational resources, SCOT first introduces Hybrid-modal Affinity Summarization (HAS) to compact salient relationships in the affinity matrix from the reference image patches and modification tokens. Furthermore, to mitigate the over-confidence in local noise, SCOT adaptively assigns optimal transport weights on the salient aligned fragments to Retain Prototype from Alignments (RAS) and guides discriminant semantics learning to Update Semantics from Enhanced Embeddings (USEE), while preserving the characteristics from global structures. Specifically, RAS module investigates the preserved semantics from the reference image based on the affinity matrix, meanwhile USEE module distills significant modification semantics. The proposed SCOT has demonstrated advanced experimental performances on widely-used datasets FashionIQ, CIRR, and Fashion200K. Ablative studies manifest the effectiveness of optimal transport guidance on preserved visual prototypes and updated semantics.