A two-stage HDR reconstruction pipeline for extreme dark-light RGGB images.

RGGB sensor arrays are commonly used in digital cameras and mobile photography. However, images of extreme dark-light conditions often suffer from insufficient exposure because the sensor receives insufficient light. The existing methods mainly employ U-Net variants, multi-stage camera parameter simulation, or image parameter processing to address this issue. However, those methods usually apply color adjustments evenly across the entire image, which may cause extensive blue or green noise artifacts, especially in images with dark backgrounds. This study attacks the problem by proposing a novel multi-step process for image enhancement. The pipeline starts with a self-attention U-Net for initial color restoration and applies a Color Correction Matrix (CCM). Thereafter, High Dynamic Range (HDR) image reconstruction techniques are utilized to improve exposure using various Camera Response Functions (CRFs). After removing under- and over-exposed frames, pseudo-HDR images are created through multi-frame fusion. Also, a comparative analysis is conducted based on a standard dataset, and the results show that the proposed approach performs better in creating well-exposed images and improves the Peak-Signal-to-Noise Ratio (PSNR) by 0.16 dB compared to the benchmark methods.