Retinex-Based Light Source Generation for Relighting up Night Photography

Abstract

Purpose: The lighting up of buildings is one of the entertainments that make a city more colorful, and photographer sometimes changes the lighting by using photo-editing applications. This paper proposes a method for automatically performing such an application that follows the Retinex theory. The Retinex theory indicates that the complex scenes caught by the human visual system are decomposed into illumination and reflectance components. Many Retinex applications take much cost into the decomposition, while we show that the decomposition accuracy is less dependent on the final output for the nightscape relighting. Methods: First, we propose an extracting method of a relighting saliency map using Retinex with edge-preserving filtering. Second, we propose a sampling method to specify the lighting area in the limited area. We show that relighting within the limited area can be represented without illumination and reflectance decomposition. We then show that this fact can be exploited to realize this application using a simple Retinex decomposition of the single-scale Retinex with fast edge-preserving filters to represent various lighting effects. Results: Experimental results show that the proposed sampling method is successful in keeping the illuminated points in bright locations and equally spaced. Also, the proposed various diffusion method can enhance night skyline photographs with various expressions. Conclusion: In this paper, we proposed a relighting method for night skyline images based on the Retinex theory. Unlike typical Retinex applications, the proposed method simplifies the process by carefully extracting the lighting points instead of performing a complex illumination and reflectance decomposition and allows various effects using various diffusion methods.