Learning Local Similarity with Spatial Relations for Object Retrieval

Many state-of-the-art object retrieval algorithms aggregate activations of convolutional neural networks into a holistic compact feature, and utilize global similarity for an efficient nearest neighbor search. However, holistic features are often insufficient for representing small objects of interest in gallery images, and global similarity drops most of the spatial relations in the images. In this paper, we propose an end-to-end local similarity learning framework to tackle these problems. By applying a correlation layer to the locally aggregated features, we compute a local similarity that can not only handle small objects, but also capture spatial relations between the query and gallery images. We further reduce the memory and storage footprints of our framework by quantizing local features. Our model can be trained using only synthetic data, and achieve competitive performance. Extensive experiments on challenging benchmarks demonstrate that our local similarity learning framework outperforms previous global similarity based methods.