Deep Photo Scan: Semi-supervised learning for dealing with the real-world degradation in smartphone photo scanning

Physical photographs now can be conveniently scanned by smartphones and stored forever as a digital version, but the scanned photos are not restored well. One solution is to train a supervised deep neural network on many digital photos and the corresponding scanned photos. However, human annotation costs a huge resource leading to limited training data. Previous works create training pairs by simulating degradation using image processing techniques. Their synthetic images are formed with perfectly scanned photos in latent space. Even so, the real-world degradation in smartphone photo scanning remains unsolved since it is more complicated due to real lens defocus, lighting conditions, losing details via printing, various photo materials, and more. To solve these problems, we propose a Deep Photo Scan (DPScan) based on semi-supervised learning. First, we present the way to produce real-world degradation and provide the DIV2K-SCAN dataset for smartphone-scanned photo restoration. Second, by using DIV2K-SCAN, we adopt the concept of Generative Adversarial Networks to learn how to degrade a high-quality image as if it were scanned by a real smartphone, then generate pseudo-scanned photos for unscanned photos. Finally, we propose to train on the scanned and pseudo-scanned photos representing a semi-supervised approach with a cycle process as: high-quality images --> real-/pseudo-scanned photos --> reconstructed images. The proposed semi-supervised scheme can balance between supervised and unsupervised errors while optimizing to limit imperfect pseudo inputs but still enhance restoration. As a result, the proposed DPScan quantitatively and qualitatively outperforms its baseline architecture, state-of-the-art academic research, and industrial products in smartphone photo scanning.