A bag-of-regions approach to sketch-based image retrieval

This paper presents a system for retrieving photographs using free-hand sketched queries. Regions are extracted from each image by gathering nodes of a hierarchical image segmentation into a bag-of-regions (BoR) representation. The BoR represents object shape at multiple scales, encoding shape even in the presence of adjacent clutter. We extract a shape representation from each region, using the Gradient Field HoG (GF-HOG) descriptor which enables direct comparison with the sketched query. The retrieval pipeline yields significant performance improvements over the previous GF-HOG results reliant on single-scale Canny edge maps, and over leading descriptors (SIFT, SSIM) for visual search. In addition, our system enables localization of the sketched object within matching images.