Deep Reinforcement Learning for Image Hashing

Deep hashing methods have received much attention recently, which achieve promising results by taking advantage of the strong representation power of deep networks. However, most existing deep hashing methods learn a whole set of hashing functions independently and directly, while ignore the correlation between different hashing functions that can promote the retrieval accuracy greatly. Inspired by the sequential decision ability of deep reinforcement learning, in this paper, we propose a new Deep Reinforcement Learning approach for Image Hashing (DRLIH). Our proposed DRLIH models the hashing learning problem as a Markov Decision Process (MDP), which learns each hashing function by correcting the errors imposed by previous ones and promotes retrieval accuracy. To the best of our knowledge, this is the first work that tries to address hashing problem from deep reinforcement learning perspective. The main contributions of our proposed DRLIH approach can be summarized as follows: (1) We propose a deep reinforcement learning hashing network. In our proposed DRLIH approach, we utilize recurrent neural network (RNN) as agents to model the hashing functions, which take actions of projecting images into binary codes sequentially, so that current hashing function learning can take previous hashing functions’ error into account. (2) We propose a sequential learning strategy based on proposed DRLIH. We define the state as a tuple of internal features of RNN’s hidden layers and image features, which can well reflect history decisions made by the agents. We also propose an action group method to enhance the correlation of the hash functions in the same group. Experiments on three widely-used datasets demonstrate the effectiveness of our proposed DRLIH approach.