DualSR: Zero-Shot Dual Learning for Real-World Super-Resolution

Advanced methods for single image super-resolution (SISR) based upon Deep learning have demonstrated a remarkable reconstruction performance on downscaled images. However, for real-world low-resolution images (e.g. images captured straight from the camera) they often generate blurry images and highlight unpleasant artifacts. The main reason is the training data that does not reflect the real-world super-resolution problem. They train the network using images downsampled with an ideal (usually bicubic) kernel. However, for real-world images the degradation process is more complex and can vary from image to image. This paper proposes a new dual-path architecture (DualSR) that learns an image-specific low-to-high resolution mapping using only patches of the input test image. For every image, a downsampler learns the degradation process using a generative adversarial network, and an upsampler learns to super-resolve that specific image. In the DualSR architecture, the upsampler and downsampler are trained simultaneously and they improve each other using cycle consistency losses. For better visual quality and eliminating undesired artifacts, the upsampler is constrained by a masked interpolation loss. On standard benchmarks with unknown degradation kernels, DualSR outperforms recent blind and non-blind super-resolution methods in term of SSIM and generates images with higher perceptual quality. On real-world LR images it generates visually pleasing and artifact free results.