Implicit Retinex Decomposition with Chromaticity Disentanglement for Low-Light Image Enhancement

Low-light image enhancement aims to improve brightness, suppress noise, and recover accurate color and structure, requiring precise illumination modeling and reliable reflectance recovery. However, most Retinex-based methods adopt explicit, multi-stage pipelines prone to decomposition bias, error accumulation, and chromatic entanglement between illumination and reflectance. To tackle these issues, we propose IDAR (Implicit Decomposition, illumination Adjustment, and reflectance Restoration), a unified Retinex-inspired framework with two key innovations. First, we design an implicit decomposition strategy based on dual-branch feature learning: a low-frequency-constrained illumination branch models lighting with chromaticity awareness, while a contrast-guided reflection branch preserves details by decoupling reflectance from illumination. This implicit design avoids intermediate supervision and reduces decomposition bias. Second, we introduce the Illumination Chromaticity Expansion Module (ICEM), which employs text-guided chromaticity learning to enhance chromaticity perception. By learning a reflectance-independent spectral representation, ICEM reduces color shifts and improves fidelity under complex lighting. Experiments on multiple benchmarks validate the superior visual quality, quantitative performance, and physical interpretability of IDAR.