ChebyLighter: Optimal Curve Estimation for Low-light Image Enhancement

Low-light enhancement aims to recover a high contrast normal light image from a low-light image with bad exposure and low contrast. Inspired by curve adjustment in photo editing software and Chebyshev approximation, this paper presents a novel model for brightening low-light images. The proposed model, ChebyLighter, learns to estimate pixel-wise adjustment curves for a low-light image recurrently to reconstruct an enhanced output. In ChebyLighter, Chebyshev image series are first generated. Then pixel-wise coefficient matrices are estimated with Triple Coefficient Estimation (TCE) modules and the final enhanced image is recurrently reconstructed by Chebyshev Attention Weighted Summation (CAWS). The TCE module is specifically designed based on dual attention mechanism with three necessary inputs. Our method can achieve ideal performance because adjustment curves can be obtained with numerical approximation by our model. With extensive quantitative and qualitative experiments on diverse test images, we demonstrate that the proposed method performs favorably against state-of-the-art low-light image enhancement algorithms.