Back Projection Generative Strategy for Low and Normal Light Image Pairs With Enhanced Statistical Fidelity and Diversity

Low light image enhancement (LLIE) using supervised deep learning is limited by the scarcity of matched low/normal light image pairs. We propose Back Projection Normal-to-Low Diffusion Model (N2LDiff-BP), a novel diffusion-based generative model that realistically transforms normal-light images into diverse low-light counterparts. By injecting noise perturbations over multiple timesteps, our model synthesizes low-light images with authentic noise, blur, and color distortions. We introduce innovative architectural components - Back Projection Attention, BP2 Feedforward, and BP Transformer Blocks - that integrate back projection to model the narrow dynamic range and nuanced noise of real low-light images. Experiment and results show N2LDiff-BP significantly outperforms prior augmentation techniques, enabling effective data augmentation for robust LLIE. We also introduce LOL-Diff, a large-scale synthetic low-light dataset. Our novel framework, architectural innovations, and dataset advance deep learning for low-light vision tasks by addressing data scarcity. N2LDiff-BP establishes a new state-of-the-art in realistic low-light image synthesis for LLIE.