# Illuminant Adaptive Wideband Image Synthesis Using Separated Base-Detail Layer Fusion Maps
## 3 Proposed method
### Base Layer Synthesis
Figure 7 shows the average synthesis results of the visible-light and near-infrared luminance base layer for comparison with the synthesis results of the visible-light and near-infrared image base layer. Figure 6: Comparison of results based on the bilateral filter map and the luminance saturation region map: (**a**) visible-light image, (**b**) near-infrared intensity image, (**c**) base layer synthesis result with the bilateral filter map, (**d**) base layer synthesis result with the joint bilateral filter map. Next, synthetic maps were added to reflect the characteristics of the nearest infrared images that appear differently between day and night, along with the joint bilateral filter. In the daytime visible-light image, a low-brightness area that inhibits visibility due to shade or backlight, such as the center of the tree in Figure 8b, is generated, and the boundary information is not expressed. In contrast, in the daytime near-infrared image, light penetration and diffusion phenomena caused by IR natural light in the tree shade area, as shown in Figure 8c, secures a large amount of light compared to visible light and increases visibility, including boundary information. The characteristics of this daytime near-infrared image are visible through the car image of visible-light and near-infrared rays in Figure 8d, and it can be seen that a large difference occurs in the area where IR penetration occurs. In the nighttime visible-light image, the border information is weak for shaded areas, such as the box in Figure 9b, and has a low luminance value on average. In contrast, in the nighttime near-infrared Figure 9c, IR auxiliary light complements the lack of light in the box and secures the boundary information of the color chart in the box. However, unlike natural light, auxiliary light is weak in long-range IR infiltration and diffusion, and short-range luminance saturation caused by the front filter of the IR flash is relatively strong. This can be confirmed by the characteristics of the night image using the auxiliary light and the change in the luminance in the cup area where saturation occurs when comparing the box and the cup area in Figure 9d. Therefore, brighter daytime visibility and near-infrared car images reflect IR light penetration, and brighter visible-light and near-infrared car images show anterior luminance saturation by IR auxiliary light. To synthesize the characteristics of these day and night images, an IR depth compensation map was applied at night, and a penetration compensation map was applied during the day. Figure 7: Base layer synthesis results: (**a**) visible-light image base layer, (**b**) near-infrared image base layer, (**c**) average synthesis result of luminance base layers, (**d**) proposed base layer synthesis result. Figure 8: Color maps of daytime images: (**a**) daytime visible and near-infrared images (**b**) daytime visible images, (**c**) daytime near-infrared images, (**d**) difference images between daytime visible and near-infrared. Figure 9: Color maps of nighttime images: (**a**) night visible and near-infrared images, (**b**) night visible images, (**c**) night near-infrared images, (**d**) difference images between nighttime visible and near-infrared. Because the night near-infrared image uses the IR assist light from the front, the difference between the visible-light image and the luminance value is oversaturated in the objects closer to the camera and shows the characteristics of the depth map, where the difference becomes weaker as the distance increases. Therefore, in the near-infrared image, it is necessary to increase the synthesis ratio of the non-saturated visible-light image so that the boundary information is well-preserved in the forward saturation region owing to the auxiliary light projection. In this case, the halo phenomenon that may occur during local tone mapping is minimized by using the difference image of the base layer image to which the bilateral filter is applied.