Learning Distinguishable Degradation Maps for Unknown Image Super-Resolution

Most existing super-resolution (SR) methods assume that the degradation is fixed (e.g., bicubic downsampling), whereas their performance would be degraded if the actual degradation differs from this assumption. To deal with unknown degradations, existing unknown SR methods are committed to learning degradation representation to generate high-resolution images. Nevertheless, they ignore that the impact of degradations on images is related to image content, or they learn degradation representations without any constraints. In this article, we propose a degradation maps extractor for unknown SR. Specifically, we learn degradation maps and condense them into a one-dimensional representation space to distinguish various degradations, which obtains distinguishable degradation maps and preserves the connection with the image contents. Furthermore, we propose a degradation map-guided SR (DMGSR) network, in which the degradation maps adaptively influence the SR process by applying channel attention and spatial attention to middle features. With the cooperation of the degradation maps extractor and the degradation maps-guided SR network, our network can flexibly handle various degradations. Experimental results show that our model achieves state-of-the-art performance in quantitative and qualitative metrics for the unknown SR task.