# Illuminant Adaptive Wideband Image Synthesis Using Separated Base-Detail Layer Fusion Maps
###### Abstract  
In this study, we present a wideband image synthesis technique for day and night object identification. To synthesize the visible and near-infrared images, a base component and a detailed component are first decomposed using a bilateral filter, and the detailed component is synthesized using a local variance map. In addition, considering the difference in the near-infrared image characteristics between daytime and nighttime, the base components are synthesized using a luminance saturation region map and depth and penetration map using a joint bilateral filter. The proposed method overcomes the partial over- or under-exposure caused by sunlight and infrared auxiliary light, which is experienced variously in wideband imaging, and improves the identification of objects in various indoor and outdoor images compared with that achieved by existing methods by emphasizing detailed components. visible and near-infrared image fusion; joint bilateral filter; base-detail layer decomposition; IR switching image; color correction +
Footnote †:  
In the case of night image capture, IR LED lighting, which does not have a visual impact, is generally used for image acquisition for security or crime prevention. It can be difficult to adjust the brightness of the LED light according to the environment. Visible and near-infrared image synthesis algorithms proposed by [PERSON] and [PERSON] et al. synthesized luminance channels using a weight map including local contrast and entropy, and synthesized images through post-processing of sharpening and color compensation [2; 3]. However, detailed information of the near-infrared image cannot be reproduced accurately, and the boundary information is not well-defined after color compensation [1]. In this study, we produced an image with excellent color expression and boundary contrast of detailed information through a synthesis method suitable for both day and night environments, and with visible-light and near-infrared images taken temporally separated. At night, multiple images are acquired by repeatedly operating IR illumination at regular unit time intervals, and the synthesis algorithm adaptively adjusts the synthesis ratio. The proposed method can obtain matching of the viewing angles of the visible and near-infrared images and sufficient brightness from time-division image acquisition using IR lighting switching. It has advantages in terms of border contrast. The proposed image processing part consists of the base-detail layer decomposition, the base layer synthesis, the detail layer synthesis, and the color compensation and adjustment. Each part is processed in the LAB color space to preserve the color information of a visible-light image. The base-detail layer decomposition part decomposes the input image into base and detail layers using the bilateral filter. The bilateral filter smooths the input image while preserving its main edges. The base layer is the bilateral filtered output of the input image, and the detail layer is the difference between the input image and the base layer. The proposed method applies different weight maps to the base image and the detail image to independently synthesize them, then sets the base and detail layers in the luminance channel. The base layer synthesis reduces the local contrast according to the near-infrared distribution characteristics of day and night. The detail layer synthesis acquires detailed information from the near-infrared image that cannot be expressed in the visible-light image. The process is carried out considering detailed information regarding the area where near-infrared rays do not pass depending on the medium. Then the fused luminance image is obtained by adding the synthesized base layer and detail layer. Finally, a resulting image is generated through a color compensation and adjustment step using the ratio of change between the luminance channel of the visible-light image and the fused luminance channel.