CSPN: A Category-specific Processing Network for Low-light Image Enhancement

Images captured in low-light conditions usually suffer from degradation problems. Recently, numerous deep learning-based methods are proposed for low-light image enhancement. They either focus on performance improvement with negligence of computational complicity, or are extremely computationally efficient networks with poor performance. In this work, we intend to figure out a solution, which strikes a balance between computational cost and performance. Moreover, we observe that different regions of an image contain different amounts of information, where the region with less information is easier to restore than that with more information. Hence, we propose to crop a low-light image into patches and classify these patches into "simple", "medium" and "hard" categories based on their involved information. Then, we enhance different patch categories with different network complexities, therefore, a Category-specific Processing Network (CSPN) is proposed to achieve the computational complexity and performance balance. The patch classification is implemented by the proposed Grey-Level Co-occurrence Matrix (GLCM) entropy-based algorithm, which measures the content complexity of an image by analyzing the statistics of the difference between pixels. As the frequency domain contains exclusive feature information that is beneficial for improving image quality, the wavelet transform is introduced during the enhancement. Extensive experimental results demonstrate the superiority of our proposed CSPN over other state-of-the-art methods in various datasets with the least amount of computational cost.