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Data augmentation via photo-to-sketch translation for sketch-based image retrieval

Sketch-based image retrieval (SBIR) technique has progressed by deep learning to learn cross-modal distance metrics that relate sketches and photos from a large number of sketch-photo pairs. However, datasets of sketch-photo pairs are small, as acquisition of a large number of such pairs is expensive. To alleviate the issue, data augmentation via image transformation such as scaling, flipping, rotation, and deformation has been widely adopted. Still, insufficiency in training set seems to have impeded deep learning from achieving its full potential for SBIR. In this paper, we propose a novel data augmentation approach dedicated for SBIR. A deep neural network called Photo2Sketch (P2S) converts photos into line drawings that are visually similar to those sketched by human. An artificially augmented training dataset of sketch-photo pairs is generated at low cost by feeding photos from a large image corpus into the P2S. Experiments evaluate quality of sketch-like images generated by the P2S as well as efficacy of the proposed data augmentation algorithm under SBIR scenario. In particular, retrieval accuracy is significantly improved when the proposed algorithm is combined with the data augmentation by image transformation