Enhancing Backlight and Spotlight Images by the Retinex-Inspired Bilateral Filter SuPeR-B

Backlight and spotlight images are pictures where the light sources generate very bright and very dark regions. The enhancement of such images has been poorly investigated and is particularly hard because it has to brighten the dark regions without over-enhance the bright ones. The solutions proposed till now generally perform multiple enhancements or segment the input image in dark and bright regions and enhance these latter with different functions. In both the cases, results are merged in a new image, that often must be smoothed to remove artifacts along the edges. This work describes SuPeR-B, a novel Retinex inspired image enhancer improving the quality of backligt and spotlight images without needing for multi-scale analysis, segmentation and smoothing. According to Retinex theory, SuPeR-B re-works the image channels separately and rescales the intensity of each pixel by a weighted average of intensities sampled from regular sub-windows. Since the rescaling factor depends both on spatial and intensity features, SuPeR-B acts like a bilateral filter. The experiments, carried out on public challenging data, demonstrate that SuPeR-B effectively improves the quality of backlight and spotlight images and also outperforms other state-of-the-art algorithms.