Improving Face Sketch Recognition via Adversarial Sketch-Photo Transformation

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feature learning [7]-[10]. The benefit of the former category relates to the conversion of sketches into the same modality as photos, and hence lies in the ability to utilize existing photo-based face recognition methods. Thus, the applicability of the existing photo-based face recognition algorithms can be greatly expanded. Current methods for face photo-sketch transformation can be mainly grouped into example-based methods and regression-based methods. Example-based methods assume that the corresponding sketches (or patches of sketches) of two similar face photos (or patches of face photos) are also similar. Such methods rely on face photo-sketch pairs in the training set to synthesize images. In order to achieve good transformation results, these methods usually require a large number of photo-sketch pairs. However, the computational cost may also grow linearly with the increase of the training set size. Regression-based methods overcome the issues mentioned above and the most time-consuming part only exists in the training stage when learning the mapping between face photos and sketches, but the inference/testing stage can be fast. In this paper, we propose a Generative Adversarial Network (GAN) for face sketch-to-photo transformation , leveraging the advantages of CycleGAN [11] and conditional GANs [12]. We have designed a new feature-level loss, which is jointly used with the traditional image-level adversarial loss to ensure the quality of the synthesized photos. The proposed approach outperforms state-of-the-art approaches for synthesizing photos in terms of structural similarity index (SSIM). More importantly, the synthesized photos of our approach are found to be more instrumental in improving the sketch-to-photo matching accuracy. The rest of this paper is organized as follows: Section II summarizes representative methods of face photo-to-sketch transformation, and GANs. Section III provides details of the proposed method and the designed feature-level loss. Experimental results and analysis are presented in Section IV. Finally, we conclude this work in Section V. Abstract-Face sketch-photo transformation has broad applications in forensics, law enforcement, and digital entertainment, particular for face recognition systems that are designed for photo-to-photo matching. While there are a number of methods for face photo-to-sketch transformation, studies on sketch-to-photo transformation remain limited. In this paper, we propose a novel conditional CycleGAN for face sketch-to-photo transformation. Specifically, we leverage the advantages of CycleGAN and conditional GANs and design a feature-level loss to assure the high quality of the generated face photos from sketches. The generated face photos are used, as a replacement of face sketches, and particularly for face identification against a gallery set of mugshot photos. Experimental results on the public-domain database CUFSF show that the proposed approach is able to generate realistic photos from sketches, and the generated photos are instrumental in improving the sketch identification accuracy against a large gallery set.

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