Fast Structural Binary Coding

Abstract

Binary coding techniques, which compress originally high-dimensional data samples into short binary codes, are becoming increasingly popular due to their efficiency for information retrieval. Leveraging supervised information can dramatically enhance the coding quality, and hence improve search performance. There are few methods, however, that efficiently learn coding functions that optimize the precision at the top of the Hamming distance ranking list while approximately preserving the geometric relationships between database examples. In this paper, we propose a novel supervised binary coding approach, namely Fast Structural Binary Coding (FSBC), to optimize the precision at the top of a Hamming distance ranking list and ensure that similar images can be returned as a whole. The key idea is to train disciplined coding functions by optimizing a lower bound of the area under the ROC (Receiver Operating Characteristic) curve (AUC) and penalize this objective so that the geometric relationships between database examples in the original Euclidean space are approximately preserved in the Hamming space. To find such a coding function, we relax the original discrete optimization objective with a continuous surrogate, and then derive a stochastic gradient descent method to optimize the surrogate objective efficiently. Empirical studies based upon two image datasets demonstrate that the proposed binary coding approaches achieve superior image search performance to the states-of-the-art.