Deep Multi-label Hashing for Large-Scale Visual Search Based on Semantic Graph

Huge volumes of images are aggregated over time because many people upload their favorite images to various social websites such as Flickr and share them with their friends. Accordingly, visual search from large scale image databases is getting more and more important. Hashing is an efficient technique to large-scale visual content search, and learning-based hashing approaches have achieved great success due to recent advancements of deep learning. However, most existing deep hashing methods focus on single label images, where hash codes cannot well preserve semantic similarity of images. In this paper, we propose a novel framework, deep multi-label hashing (DMLH) based on a semantic graph, which consists of three key components: (i) Image labels, semantically similar in terms of co-occurrence relationship, are classified in such a way that similar labels are in the same cluster. This helps to provide accurate ground truth for hash learning. (ii) A deep model is trained to simultaneously generate hash code and feature vector of images, based on which multi-label image databases are organized by hash tables. This model has excellent capability in improving retrieval speed meanwhile preserving semantic similarity among images. (iii) A combination of hash code based coarse search and feature vector based fine image ranking is used to provide an efficient and accurate retrieval. Extensive experiments over several large image datasets confirm that the proposed DMLH method outperforms state-of-the-art supervised and unsupervised image retrieval approaches, with a gain ranging from 6.25% to 38.9% in terms of mean average precision.